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From pgsql-hackers-owner+M174@hub.org Sun Mar 12 22:31:11 2000
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From: Bruce Momjian <pgman@candle.pha.pa.us>
Message-Id: <200003130359.WAA25403@candle.pha.pa.us>
Subject: [HACKERS] Fix for RENAME
To: PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: Sun, 12 Mar 2000 22:59:56 -0500 (EST)
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Status: RO
I have thought about the issue with ALTER TABLE RENAME and keeping the
file system in sync with the database.
It seems there are three commands that can cause these to get out of
sync:
CREATE TABLE/INDEX
DROP TABLE/INDEX
ALTER TABLE RENAME
Now, if we had file names based only on the oid, we can eliminate file
renaming for RENAME, but the others are still a problem.
Seems there are three ways to get out of sync:
ABORT transaction
backend crash
OS crash
The last two are the same, except the backend crash restarts the
postmaster, while the OS crash has the postmaster starting up normally.
Here is my idea. Create a C List of file names to unlink on transaction
commit or abort. For CREATE, unlink created files on transaction ABORT.
For DROP, unlink dropped files on COMMIT. For RENAME, create a hard
link for the new table linked to old table, and unlink the old file name
on COMMIT or the new file on ABORT.
That takes care of COMMIT and ABORT. For backend crash or OS crash, add
a postgres command-line flag for recovery. Have the postmaster on
startup or shared memory refresh start up a postgres backend on every
database with the recovery flag set. Have the postgres backend find all
the oids in the pg_class table, and have it go through every file in the
database directory and remove all files that don't match the oids/names
in pg_class. Also, remove all old sort, noname, and temp files at the
same time. Seems we should be doing this anyway.
Care would have to be taken that a corrupted database that caused a
postgres crash on connection would not get the postmaster startup into
an infinite loop.
Comments?
--
Bruce Momjian | http://www.op.net/~candle
pgman@candle.pha.pa.us | (610) 853-3000
+ If your life is a hard drive, | 830 Blythe Avenue
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026
From reedstrm@wallace.ece.rice.edu Tue Mar 14 12:33:31 2000
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Date: Tue, 14 Mar 2000 12:33:32 -0600
From: "Ross J. Reedstrom" <reedstrm@wallace.ece.rice.edu>
To: Hiroshi Inoue <Inoue@tpf.co.jp>
Cc: Bruce Momjian <pgman@candle.pha.pa.us>,
PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: [HACKERS] Fix for RENAME
Message-ID: <20000314123331.A6094@rice.edu>
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Status: RO
Hiroshi -
I've just about finished working up a patch to store the physical
file name in the pg_class table. There are only two places that
require a Rule for generating the filename, and one of them is
only used for bootstrapping. For the initial cut, I used the rule:
The filename consists of the TABLENAME, and underscore, and the OID.
If this is longer than NAMEDATALEN, shorten the TABLENAME.
I implemented this rule by exporting Tom's makeObjectName function
from analyze.c, which is used to make other system generated names
that are have a requirement to be human readable. Replacing this
rule with any other in the future would be straightforward, except
for bootstrap. There are a number of places in bootstrap that need to
know the filename. I've factored them out into yet another set of
#defines (in catname.h) to make that easier.
I'm working through the regression tests right now: this is a relatively
extensive change, since it modifies the low level access routines, and the
buffer cache (which I indexed on physical filename, rather than relname,
as it is now) Hopefully, I caught all the places that assume relname ==
filename == unique name within a single database (see, I want schemas...)
Ross
--
Ross J. Reedstrom, Ph.D., <reedstrm@rice.edu>
NSBRI Research Scientist/Programmer
Computer and Information Technology Institute
Rice University, 6100 S. Main St., Houston, TX 77005
On Tue, Mar 14, 2000 at 02:24:52PM +0900, Hiroshi Inoue wrote:
> > -----Original Message-----
> > From: Bruce Momjian [mailto:pgman@candle.pha.pa.us]
> >
> > > > They use the existing table file. It is only when
> > > > adding/removing/renaming file system files that this
> > out-of-sync problem
> > > > happens.
> > > >
> >
> > Not sure. I was going to get the CREATE/DROP/RENAME working as it
> > should then as we add more features, we can implement this solution for
> > them too.
> >
>
> Hmm,is general solution difficult ?
> Is more flexible naming rule bad ?
>
> This the 3rd or 4th time that I mention the following.
>
> PostgreSQL doesn't keep the information in itself where tables are
> allocated. So we need a naming rule to find where existent tables
> are allocated. Don't you wonder the spec ?
>
> Regards.
>
> Hiroshi Inoue
> Inoue@tpf.co.jp
>
>
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Date: Tue, 14 Mar 2000 12:33:32 -0600
From: "Ross J. Reedstrom" <reedstrm@wallace.ece.rice.edu>
To: Hiroshi Inoue <Inoue@tpf.co.jp>
Cc: Bruce Momjian <pgman@candle.pha.pa.us>,
PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: [HACKERS] Fix for RENAME
Message-ID: <20000314123331.A6094@rice.edu>
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Hiroshi -
I've just about finished working up a patch to store the physical
file name in the pg_class table. There are only two places that
require a Rule for generating the filename, and one of them is
only used for bootstrapping. For the initial cut, I used the rule:
The filename consists of the TABLENAME, and underscore, and the OID.
If this is longer than NAMEDATALEN, shorten the TABLENAME.
I implemented this rule by exporting Tom's makeObjectName function
from analyze.c, which is used to make other system generated names
that are have a requirement to be human readable. Replacing this
rule with any other in the future would be straightforward, except
for bootstrap. There are a number of places in bootstrap that need to
know the filename. I've factored them out into yet another set of
#defines (in catname.h) to make that easier.
I'm working through the regression tests right now: this is a relatively
extensive change, since it modifies the low level access routines, and the
buffer cache (which I indexed on physical filename, rather than relname,
as it is now) Hopefully, I caught all the places that assume relname ==
filename == unique name within a single database (see, I want schemas...)
Ross
--
Ross J. Reedstrom, Ph.D., <reedstrm@rice.edu>
NSBRI Research Scientist/Programmer
Computer and Information Technology Institute
Rice University, 6100 S. Main St., Houston, TX 77005
On Tue, Mar 14, 2000 at 02:24:52PM +0900, Hiroshi Inoue wrote:
> > -----Original Message-----
> > From: Bruce Momjian [mailto:pgman@candle.pha.pa.us]
> >
> > > > They use the existing table file. It is only when
> > > > adding/removing/renaming file system files that this
> > out-of-sync problem
> > > > happens.
> > > >
> >
> > Not sure. I was going to get the CREATE/DROP/RENAME working as it
> > should then as we add more features, we can implement this solution for
> > them too.
> >
>
> Hmm,is general solution difficult ?
> Is more flexible naming rule bad ?
>
> This the 3rd or 4th time that I mention the following.
>
> PostgreSQL doesn't keep the information in itself where tables are
> allocated. So we need a naming rule to find where existent tables
> are allocated. Don't you wonder the spec ?
>
> Regards.
>
> Hiroshi Inoue
> Inoue@tpf.co.jp
>
>
From mascarm@mascari.com Tue Mar 14 16:34:04 2000
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From: Mike Mascari <mascarm@mascari.com>
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To: Bruce Momjian <pgman@candle.pha.pa.us>
CC: Hiroshi Inoue <Inoue@tpf.co.jp>,
PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: [HACKERS] Fix for RENAME
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Status: RO
Bruce Momjian wrote:
>
> > Hmm,is general solution difficult ?
> > Is more flexible naming rule bad ?
> >
> > This the 3rd or 4th time that I mention the following.
>
> That's because I didn't understand.
>
> >
> > PostgreSQL doesn't keep the information in itself where tables are
> > allocated. So we need a naming rule to find where existent tables
> > are allocated. Don't you wonder the spec ?
>
> How does naming the files in the database help our DROP/CREATE problem?
> It would help RENAME a little bit. Not sure about the others because
> currently they don't have a problem.
I've been thinking about this somewhat, and I think the first
step necessary in correctly supporting ROLLBACK-able DDL
statements in transactions is the change to <relname>_<oid>.
Imagine the scenario:
CREATE TABLE test (key int4);
a) Session #1:
BEGIN;
b) Session #2:
BEGIN;
DROP TABLE test;
CREATE TABLE test (value varchar(32));
c) Session #1:
DROP TABLE test;
COMMIT;
d) Session #2:
COMMIT;
What's clear to me is that, if DDL statements are to be
ROLLBACK-able, either (1) an AccessExclusive lock is held on the
relation until transaction commit (like Phillip Warner stated was
Dec/Rdb's behavior) or (2) PostgreSQL must be capable of
supporting "multi-versioned schema" as well as tuples. Before
step 'c' is executed, both tables must simultaneously exist in
the database with the same name, which works fine in the cataloge
thanks to MVCC, but requires that, on disk, there exists:
test_01231 - Session #1's table, available for ROLLBACK
test_13421 - Session #2's table, available for COMMIT
Now, I believe it was Andreas who suggested that VACUUM be
modified to perform cleanup. I agree with this. VACUUM will need
to check for aborted relation tuples in pg_class and remove the
associated file from the filesystem in the event, for example,
that Session #2 aborted -or- Session #1 aborted leaving the
original pg_class tuple the "active" one and Session #2 attempted
to COMMIT, which violates the UNIQUE constraint on the relname of
pg_class. In addition, for "active" relation entries, VACUUM
should verify the filename is
<relname>_<oid> for the given oid. If it is not, it should rename
the filename on the filesystem. Again, this is purely cosmetic
for administrative purposes only, but would allow
for lack of atomicity only with respect to the label of the
relation file, until the next
VACUUM is run.
For the case of ALTER TABLE RENAME, ALTER TABLE DROP COLUMN,
etc., the same functionality would apply. But, as in previous
discussions regarding ALTER TABLE DROP COLUMN, PostgreSQL MUST be
capable of allowing multiple tuples with different attribute
counts and types within the same relation:
CREATE TABLE test (key int4);
a) Session #1:
BEGIN;
b) Session #2:
BEGIN;
ALTER TABLE test ADD COLUMN value int4;
INSERT INTO test values (1, 1);
c) Session #1:
INSERT INTO test values (0);
COMMIT;
d) Session #2:
COMMIT;
This also means that Hiroshi's plan to suppress the visibility of
attributes for ALTER TABLE DROP COLUMN would be required anyway,
to allow for "multi-versioning" of attributes within a single
tuple (i.e., like multi-versioning of tuples within relations),
an attribute is either visible or not, but the tuple should
always grow, until, of course, the next VACUUM.
So, to support rollback-able DDL statements ("multi-versioning
schema", if you will), PostgreSQL needs:
1) relation names of the form <relname>_<oid>
2) support "multi-versioning" of attributes within a single tuple
3) modify VACUUM to:
A) Remove filesystem files whose pg_class tuples are no longer
valid
B) Rename filesystem files to relname of pg_class when the
<relname>_<oid> doesn't match
C) Reconstruct relations after attributes have been
added/dropped.
4) All DDL statements should perform their non-create filesystem
functions in the now infamous "post-transaction-commit" trigger.
If the backend should crash between the time the transaction
committed and the rename() or unlink(), no adverse affects would
be encountered with the database WRT data, VACUUM would clean up
the rename() problem, and, worst-case scenario, an old
<relname>_<oid> file would lie around unused. But at least it
would no longer prohibit the creation of a table by the same
name....
Just my humble opinion,
Mike Mascari
From Inoue@tpf.co.jp Tue Mar 14 20:31:35 2000
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From: "Hiroshi Inoue" <Inoue@tpf.co.jp>
To: "Ross J. Reedstrom" <reedstrm@wallace.ece.rice.edu>,
"Bruce Momjian" <pgman@candle.pha.pa.us>
Cc: "PostgreSQL-development" <pgsql-hackers@postgresql.org>
Subject: RE: [HACKERS] Fix for RENAME
Date: Wed, 15 Mar 2000 11:35:46 +0900
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> -----Original Message-----
> From: Ross J. Reedstrom [mailto:reedstrm@wallace.ece.rice.edu]
>
> Hiroshi -
> I've just about finished working up a patch to store the physical
> file name in the pg_class table. There are only two places that
> require a Rule for generating the filename, and one of them is
> only used for bootstrapping.
Thanks for your trial.
It's nice that only two places require naming rule.
I don't stick to one naming rule.
The only limitation is the uniqueness and the rule
could be changed according to situations.
For example,we could change the naming rule according to
the kind of relation such as system/user relations.
I'm now inclined to introduce a new system relation to store
the physical path name. It could also have table(data)space
information in the (near ?) future.
It seems better to separate it from pg_class because table(data?)
space may change the concept of table allocation.
Comments ?
Regards.
Hiroshi Inoue
Inoue@tpf.co.jp
From Inoue@tpf.co.jp Wed Mar 15 02:00:58 2000
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From: "Hiroshi Inoue" <Inoue@tpf.co.jp>
To: "Bruce Momjian" <pgman@candle.pha.pa.us>
Cc: "Ross J. Reedstrom" <reedstrm@wallace.ece.rice.edu>,
"PostgreSQL-development" <pgsql-hackers@postgresql.org>
Subject: RE: [HACKERS] Fix for RENAME
Date: Wed, 15 Mar 2000 17:00:35 +0900
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> -----Original Message-----
> From: Bruce Momjian [mailto:pgman@candle.pha.pa.us]
>
> > I'm now inclined to introduce a new system relation to store
> > the physical path name. It could also have table(data)space
> > information in the (near ?) future.
> > It seems better to separate it from pg_class because table(data?)
> > space may change the concept of table allocation.
>
> Why not just put it in pg_class?
>
Not sure,it's only my feeling.
Comments please,everyone.
We have taken a practical way which doesn't break file per table
assumption in this thread and it wouldn't so difficult to implement.
In fact Ross has already tried it.
However there was a discussion about data(table)space for
months ago and currently a new discussion is there.
Judging from the previous discussion,I can't expect so much
that it could get a practical consensus(How many opinions there
were). We can make a practical step toward future by encapsulating
the information of table allocation. Separating table alloc info from
pg_class seems one of the way.
There may be more essential things for encapsulation.
Comments ?
Regards.
Hiroshi Inoue
Inoue@tpf.co.jp
From pgsql-hackers-owner+M196@hub.org Thu Mar 16 03:02:35 2000
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Date: Thu, 16 Mar 2000 08:28:11 +0100 (CET)
From: Martin Neumann <mne@mne.de>
Subject: [HACKERS] RfD: Design of tablespaces
To: pgsql-hackers@postgresql.org
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Status: RO
I have written some thoughts on the concept of tablespace
down. I would be happy to get some comments on it.
-----------------------------------------------------------------
Implementation of tablespaces within PostgreSQL
- a brainstorming paper designed for general discussion -
by Martin Neumann, 2000/3/15
1. What are tablespaces?
-------------------------
Tablespaces make it possible to distribute storage objects
over multiple points of storage (POS). Therefor one could
say a tablespace can be a POS.
Example:
tablespace_a -----> /mnt/raid/arena0/
tablespace_b -----> /mnt/raid/emc0/
Tablespaces can also store their data on other tablespaces:
tablespace_c -----> tablespace_b
This is quite interessting for administration purposes.
2. What are its advantages?
----------------------------
As you can choose a different tablespace for every storage
object (table, index etc.) it is easy to improve the following
aspects of your system:
- Reliability
You can put storage objects (mostly tables) you strongly depend
on onto a more reliable tablespace (mirrored RAID or perhaps
simply a directory which gets backuped more often than others).
- Speed
You can put storage objects you rarely need onto a rather slow
tablespace and keep your quick tablespaces clean from this.
A fast, but more expensive RAID-Stripeset can be used more
efficiently as it doesn't get filled with non-performance
sensitive data.
But also distributing storage objects which have equal needs
in sense of speed onto different tablespaces makes sense as
you gain more speed by distributing data over more than one
harddisk spindle.
- Manageability
You can grant and revoke rights on base of a tablespace.
As every storage object belongs to exactly one tablespace,
you can easily group storage objects using a tablespace.
3. What about disk I/O?
------------------------
Tablespaces tell the storage manager only where to store
the data, not how. This is the reasonable way.
4. Usage
---------
CREATE TABLESPACE tsname TYPE storage_type storage_options
Examples:
CREATE TABLESPACE tsemc0
TYPE classic DIRECTORY /mnt/raid/emc0 NOFSYNC
CREATE TABLESPACE tsarena0 TYPE raw DEVICE /dev/araid/0
MINSIZE 128 MAXSIZE 4096 GROW 4 32 SHRINK 2 32
BLOCKSIZE 16384
CREATE TABLESPACE quick0 TYPE link TABLESPACE tsarena0;
--
CREATE TABLE tbname ( ... ) TABLESPACE tsname;
Examples:
CREATE TABLE foo (
id int4 NOT NULL UNIQUE,
name text NOT NULL
) TABLESPACE tsemc0;
CREATE TABLE bar (
id int4 NOT NULL UNIQUE,
name text NOT NULL
) TABLESPACE default;
If the tablespace isn't given, the storage objects gets created
in the "default" tablespace.
"default" is the PostgreSQL's default tablespace and the only one
which has to exist on each system.
--
ALTER TABLESPACE tsname tssettings
Examples:
ALTER TABLESPACE tsemc0 DIRECTORY /mnt/raid/emc1
NOTE: altering tablespaces without recreating the contained
storage objects introduces many problems.
Realisation is difficult and won't be my first goal.
--
DROP TABLESPACE tsname [FORCE]
Examples:
DROP TABLESPACE tsarena0
This will immediately remove the tablespace tsarena0
if it contains no storage objects.
If it still contains some the tablespace is marked for
deletion.
This means:
1. you can't create new storage objects in the tablespace
2. if the last storage object inside gets dropped, the
tablespace will be removed.
DROP TABLESPACE tsarena0 FORCE
This will remove the tablespace including all contained
storage objects immediately.
--
VACUUM tsname
Example:
VACUUM tsemc1
This will vacuum a single tablespace with all contained
storage objects.
-----------------------------------------------------------------
--
Martin Neumann, Welkenrather Str. 118c, 52074 Aachen, Germany
mne@mne.de - http://www.mne.de/mne/ - sms@mne.de [eMail2SMS]
Tel. 0241 / 8876-080 - Mobil: 0173 / 27 69 632
..------.---------------------------------------------------------
| at | Inform GmbH - Abteilung Airport Logistics
| work | Pascalstr. 23 - 52076 Aachen - Tel. 02408 / 9456-0
|______| martin.neumann@inform-ac.com - http://www.inform-ac.com
From JanWieck@t-online.de Wed Jun 14 19:01:01 2000
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Wed, 14 Jun 2000 22:43:39 +0200
From: JanWieck@t-online.de (Jan Wieck)
Message-Id: <200006142043.WAA07887@hot.jw.home>
Subject: Re: [HACKERS] Big 7.1 open items
In-Reply-To: <14752.960996980@sss.pgh.pa.us> from Tom Lane at "Jun 14, 2000 11:36:20
am"
To: Tom Lane <tgl@sss.pgh.pa.us>
Date: Wed, 14 Jun 2000 22:43:39 +0200 (MEST)
CC: Oliver Elphick <olly@lfix.co.uk>, Bruce Momjian <pgman@candle.pha.pa.us>,
PostgreSQL-development <pgsql-hackers@postgresql.org>
Reply-To: Jan Wieck <JanWieck@Yahoo.com>
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Status: ROr
Tom Lane wrote:
> "Oliver Elphick" <olly@lfix.co.uk> writes:
> > I suggest that DROP TABLE in a transaction should not be allowed.
>
> I had actually made it do that for a short time early this year,
> and was shouted down. On reflection I have to agree; it's too useful
> to be able to do
>
> begin;
> drop table foo;
> create table foo(new schema);
> ...
> end;
>
> You do indeed lose big if you suffer an error partway through, but
> the answer to that is to fix our file naming conventions so that we
> can support rollback of drop table.
Belongs IMHO to the discussion to keep separate what is
separate (having indices/toast-relations/etc. in separate
directories and whatnot).
I've never been really happy with the file naming
conventions. The need of a filesystem entry to have the same
name of the DB object that is associated with it isn't right.
I know, some people love to be able to easily identify the
files with ls(1). OTOH what is that good for?
Well, someone can easily see how big the disk footprint of
his data is. Whow - what an info. Anything else?
Why not changing the naming to be something like this:
<dbroot>/catalog_tables/pg_...
<dbroot>/catalog_index/pg_...
<dbroot>/user_tables/oid_...
<dbroot>/user_index/oid_...
<dbroot>/temp_tables/oid_...
<dbroot>/temp_index/oid_...
<dbroot>/toast_tables/oid_...
<dbroot>/toast_index/oid_...
<dbroot>/whatnot_???/...
This way, it would be much easier to separate all the
different object types to different physical media. We would
loose some transparency, but I've allways wondered what
people USE that for (except for just wanna know). For
convinience we could implement another little utility that
tells the object size like
DESCRIBE TABLE/VIEW/whatnot <object-name>
that returns the physical location and storage details of the
object. And psql could use it to print this info additional
on the \d commands. Would give unprivileged users access to
this info, so be it, it's not a security issue IMHO.
The subdirectory an object goes into has to be controlled by
the relkind. So we need to tidy up that a little too. I think
it's worth it.
The objects storage location (the bare file) now would
contain the OID. So we avoid naming conflicts for temp
tables, naming conflicts during DROP/CREATE in a transaction
and all the like.
Comments?
Jan
--
#======================================================================#
# It's easier to get forgiveness for being wrong than for being right. #
# Let's break this rule - forgive me. #
#================================================== JanWieck@Yahoo.com #
From tgl@sss.pgh.pa.us Wed Jun 14 22:06:54 2000
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To: Jan Wieck <JanWieck@Yahoo.com>
cc: Oliver Elphick <olly@lfix.co.uk>, Bruce Momjian <pgman@candle.pha.pa.us>,
PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: [HACKERS] Big 7.1 open items
In-reply-to: <200006142043.WAA07887@hot.jw.home>
References: <200006142043.WAA07887@hot.jw.home>
Comments: In-reply-to JanWieck@t-online.de (Jan Wieck)
message dated "Wed, 14 Jun 2000 22:43:39 +0200"
Date: Wed, 14 Jun 2000 22:07:15 -0400
Message-ID: <16606.961034835@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
Status: RO
JanWieck@t-online.de (Jan Wieck) writes:
> I've never been really happy with the file naming
> conventions. The need of a filesystem entry to have the same
> name of the DB object that is associated with it isn't right.
> I know, some people love to be able to easily identify the
> files with ls(1). OTOH what is that good for?
I agree with Jan on this: let's just change the file names over to
be OIDs. Then we can have rollbackable DROP and RENAME TABLE easily.
Naming the files after the logical names of the tables is nice if it
doesn't cost anything, but it is *not* worth the trouble to preserve
a relationship between filename and tablename when it is costing us.
And it's costing us big time. That single feature is hurting us on
functionality, robustness, and portability, and for what benefit?
Not nearly enough. It's time to just let go of it.
> Why not changing the naming to be something like this:
> <dbroot>/catalog_tables/pg_...
> <dbroot>/catalog_index/pg_...
> <dbroot>/user_tables/oid_...
> <dbroot>/user_index/oid_...
> <dbroot>/temp_tables/oid_...
> <dbroot>/temp_index/oid_...
> <dbroot>/toast_tables/oid_...
> <dbroot>/toast_index/oid_...
> <dbroot>/whatnot_???/...
I don't see a lot of value in that. Better to do something like
tablespaces:
<dbroot>/<oidoftablespace>/<oidofobject>
regards, tom lane
From tgl@sss.pgh.pa.us Wed Jun 14 22:20:59 2000
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Wed, 14 Jun 2000 22:21:30 -0400 (EDT)
To: Bruce Momjian <pgman@candle.pha.pa.us>
cc: Jan Wieck <JanWieck@Yahoo.com>, Oliver Elphick <olly@lfix.co.uk>,
PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: [HACKERS] Big 7.1 open items
In-reply-to: <200006142313.TAA22904@candle.pha.pa.us>
References: <200006142313.TAA22904@candle.pha.pa.us>
Comments: In-reply-to Bruce Momjian <pgman@candle.pha.pa.us>
message dated "Wed, 14 Jun 2000 19:13:47 -0400"
Date: Wed, 14 Jun 2000 22:21:30 -0400
Message-ID: <16705.961035690@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
Status: ROr
Bruce Momjian <pgman@candle.pha.pa.us> writes:
> You need something that works from the command line, and something that
> works if PostgreSQL is not running. How would you restore one file from
> a tape.
"Restore one file from a tape"? How are you going to do that anyway?
You can't save and restore portions of a database like that, because
of transaction commit status problems. To restore table X correctly,
you'd have to restore pg_log as well, and then your other tables are
hosed --- unless you also restore all of them from the backup. Only
a complete database restore from tape would work, and for that you
don't need to tell which file is which. So the above argument is a
red herring.
I realize it's nice to be able to tell which table file is which by
eyeball, but the price we are paying for that small convenience is
just too high. Give that up, and we can have rollbackable DROP and
RENAME now (I'll personally commit to making it happen for 7.1).
Continue to insist on it, and I don't think we'll *ever* have those
features in a really robust form. It's just not possible to do
multiple file renames atomically.
regards, tom lane
From pgsql-hackers-owner+M3381@hub.org Wed Jun 14 22:23:25 2000
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Wed, 14 Jun 2000 22:21:30 -0400 (EDT)
To: Bruce Momjian <pgman@candle.pha.pa.us>
cc: Jan Wieck <JanWieck@Yahoo.com>, Oliver Elphick <olly@lfix.co.uk>,
PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: [HACKERS] Big 7.1 open items
In-reply-to: <200006142313.TAA22904@candle.pha.pa.us>
References: <200006142313.TAA22904@candle.pha.pa.us>
Comments: In-reply-to Bruce Momjian <pgman@candle.pha.pa.us>
message dated "Wed, 14 Jun 2000 19:13:47 -0400"
Date: Wed, 14 Jun 2000 22:21:30 -0400
Message-ID: <16705.961035690@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
X-Mailing-List: pgsql-hackers@postgresql.org
Precedence: bulk
Sender: pgsql-hackers-owner@hub.org
Status: ROr
Bruce Momjian <pgman@candle.pha.pa.us> writes:
> You need something that works from the command line, and something that
> works if PostgreSQL is not running. How would you restore one file from
> a tape.
"Restore one file from a tape"? How are you going to do that anyway?
You can't save and restore portions of a database like that, because
of transaction commit status problems. To restore table X correctly,
you'd have to restore pg_log as well, and then your other tables are
hosed --- unless you also restore all of them from the backup. Only
a complete database restore from tape would work, and for that you
don't need to tell which file is which. So the above argument is a
red herring.
I realize it's nice to be able to tell which table file is which by
eyeball, but the price we are paying for that small convenience is
just too high. Give that up, and we can have rollbackable DROP and
RENAME now (I'll personally commit to making it happen for 7.1).
Continue to insist on it, and I don't think we'll *ever* have those
features in a really robust form. It's just not possible to do
multiple file renames atomically.
regards, tom lane
From pgsql-hackers-owner+M3382@hub.org Wed Jun 14 22:31:42 2000
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Wed, 14 Jun 2000 22:28:53 -0400 (EDT)
From: Bruce Momjian <pgman@candle.pha.pa.us>
Message-Id: <200006150228.WAA06576@candle.pha.pa.us>
Subject: Re: [HACKERS] Big 7.1 open items
In-Reply-To: <16705.961035690@sss.pgh.pa.us> "from Tom Lane at Jun 14, 2000 10:21:30
pm"
To: Tom Lane <tgl@sss.pgh.pa.us>
Date: Wed, 14 Jun 2000 22:28:53 -0400 (EDT)
CC: Jan Wieck <JanWieck@Yahoo.com>, Oliver Elphick <olly@lfix.co.uk>,
PostgreSQL-development <pgsql-hackers@postgresql.org>
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Status: RO
> Bruce Momjian <pgman@candle.pha.pa.us> writes:
> > You need something that works from the command line, and something that
> > works if PostgreSQL is not running. How would you restore one file from
> > a tape.
>
> "Restore one file from a tape"? How are you going to do that anyway?
> You can't save and restore portions of a database like that, because
> of transaction commit status problems. To restore table X correctly,
> you'd have to restore pg_log as well, and then your other tables are
> hosed --- unless you also restore all of them from the backup. Only
> a complete database restore from tape would work, and for that you
> don't need to tell which file is which. So the above argument is a
> red herring.
>
> I realize it's nice to be able to tell which table file is which by
> eyeball, but the price we are paying for that small convenience is
> just too high. Give that up, and we can have rollbackable DROP and
> RENAME now (I'll personally commit to making it happen for 7.1).
> Continue to insist on it, and I don't think we'll *ever* have those
> features in a really robust form. It's just not possible to do
> multiple file renames atomically.
>
OK, I am flexible. (Yea, right.) :-)
But seriously, let me give some background. I used Ingres, that used
the VMS file system, but used strange sequential AAAF324 numbers for
tables. When someone deleted a table, or we were looking at what tables
were using disk space, it was impossible to find the Ingres table names
that went with the file. There was a system table that showed it, but
it was poorly documented, and if you deleted the table, there was no way
to look on the tape to find out which file to restore.
As far as pg_log, you certainly would not expect to get any information
back from the time of the backup table to current, so the current pg_log
would be just fine.
Basically, I guess we have to do it, but we have to print the proper
error messages for cases in the backend we just print the file name.
Also, we have to now replace the 'ls -l' command with something that
will be meaningful.
Right now, we use 'ps' with args to display backend information, and ls
-l to show disk information. We are going to lose that here.
--
Bruce Momjian | http://www.op.net/~candle
pgman@candle.pha.pa.us | (610) 853-3000
+ If your life is a hard drive, | 830 Blythe Avenue
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026
From tgl@sss.pgh.pa.us Wed Jun 14 22:31:01 2000
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To: Bruce Momjian <pgman@candle.pha.pa.us>
Subject: Re: [HACKERS] Big 7.1 open items
In-reply-to: <200006150223.WAA06516@candle.pha.pa.us>
References: <200006150223.WAA06516@candle.pha.pa.us>
Comments: In-reply-to Bruce Momjian <pgman@candle.pha.pa.us>
message dated "Wed, 14 Jun 2000 22:23:58 -0400"
Date: Wed, 14 Jun 2000 22:31:33 -0400
Message-ID: <16780.961036293@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
Status: RO
> Can I phone you?
Sure, I'm here.
regards, tom lane
From pgsql-hackers-owner+M3383@hub.org Wed Jun 14 22:38:29 2000
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To: Bruce Momjian <pgman@candle.pha.pa.us>
cc: Jan Wieck <JanWieck@Yahoo.com>, Oliver Elphick <olly@lfix.co.uk>,
PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: [HACKERS] Big 7.1 open items
In-reply-to: <200006150228.WAA06576@candle.pha.pa.us>
References: <200006150228.WAA06576@candle.pha.pa.us>
Comments: In-reply-to Bruce Momjian <pgman@candle.pha.pa.us>
message dated "Wed, 14 Jun 2000 22:28:53 -0400"
Date: Wed, 14 Jun 2000 22:36:19 -0400
Message-ID: <16810.961036579@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
X-Mailing-List: pgsql-hackers@postgresql.org
Precedence: bulk
Sender: pgsql-hackers-owner@hub.org
Status: ROr
Bruce Momjian <pgman@candle.pha.pa.us> writes:
> But seriously, let me give some background. I used Ingres, that used
> the VMS file system, but used strange sequential AAAF324 numbers for
> tables. When someone deleted a table, or we were looking at what tables
> were using disk space, it was impossible to find the Ingres table names
> that went with the file. There was a system table that showed it, but
> it was poorly documented, and if you deleted the table, there was no way
> to look on the tape to find out which file to restore.
Fair enough, but it seems to me that the answer is to expend some effort
on system admin support tools. We could do a lot in that line with less
effort than trying to make a fundamentally mismatched filesystem
representation do what we need.
regards, tom lane
From tgl@sss.pgh.pa.us Wed Jun 14 23:13:35 2000
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To: Bruce Momjian <pgman@candle.pha.pa.us>
cc: Jan Wieck <JanWieck@Yahoo.com>, Oliver Elphick <olly@lfix.co.uk>,
PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: [HACKERS] Big 7.1 open items
In-reply-to: <200006150244.WAA27741@candle.pha.pa.us>
References: <200006150244.WAA27741@candle.pha.pa.us>
Comments: In-reply-to Bruce Momjian <pgman@candle.pha.pa.us>
message dated "Wed, 14 Jun 2000 22:44:16 -0400"
Date: Wed, 14 Jun 2000 23:13:52 -0400
Message-ID: <16985.961038832@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
Status: ROr
Bruce Momjian <pgman@candle.pha.pa.us> writes:
> That was my point --- that in doing this change, we are taking on more
> TODO items, that may detract from our main TODO items.
True, but they are also TODO items that could be handled by people other
than the inner circle of key developers. The actual rejiggering of
table-to-filename mapping is going to have to be done by one of the
small number of people who are fully up to speed on backend internals.
But we've got a lot more folks who would be able (and, hopefully,
willing) to design and code whatever tools are needed to make the
dbadmin's job easier in the face of the new filesystem layout. I'd
rather not expend a lot of core time to avoid needing those tools,
especially when I feel the old approach is fatally flawed anyway.
> Even gdb shows us the filename/tablename in backtraces. We are never
> going to be able to reproduce that.
Backtraces from *what*, exactly? 99% of the backend is still going
to be dealing with the same data as ever. It might be that poking
around in fd.c will be a little harder, but considering that fd.c
doesn't really know or care what the files it's manipulating are
anyway, I'm not convinced that this is a real issue.
> I guess I don't consider table schema commands inside transactions and
> such to be as big an items as the utility features we will need to
> build.
You've *got* to be kidding. We're constantly seeing complaints about
the fact that rolling back DROP or RENAME TABLE fails --- and worse,
leaves the table in a corrupted/inconsistent state. As far as I can
tell, that's one of the worst robustness problems we've got left to
fix. This is a big deal IMHO, and I want it to be fixed and fixed
right. I don't see how to fix it right if we try to keep physical
filenames tied to logical tablenames.
Moreover, that restriction will continue to hurt us if we try to
preserve it while implementing tablespaces, ANSI schemas, etc.
regards, tom lane
From pgsql-hackers-owner+M3387@hub.org Wed Jun 14 23:16:56 2000
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To: Bruce Momjian <pgman@candle.pha.pa.us>
cc: Jan Wieck <JanWieck@Yahoo.com>, Oliver Elphick <olly@lfix.co.uk>,
PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: [HACKERS] Big 7.1 open items
In-reply-to: <200006150244.WAA27741@candle.pha.pa.us>
References: <200006150244.WAA27741@candle.pha.pa.us>
Comments: In-reply-to Bruce Momjian <pgman@candle.pha.pa.us>
message dated "Wed, 14 Jun 2000 22:44:16 -0400"
Date: Wed, 14 Jun 2000 23:13:52 -0400
Message-ID: <16985.961038832@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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Bruce Momjian <pgman@candle.pha.pa.us> writes:
> That was my point --- that in doing this change, we are taking on more
> TODO items, that may detract from our main TODO items.
True, but they are also TODO items that could be handled by people other
than the inner circle of key developers. The actual rejiggering of
table-to-filename mapping is going to have to be done by one of the
small number of people who are fully up to speed on backend internals.
But we've got a lot more folks who would be able (and, hopefully,
willing) to design and code whatever tools are needed to make the
dbadmin's job easier in the face of the new filesystem layout. I'd
rather not expend a lot of core time to avoid needing those tools,
especially when I feel the old approach is fatally flawed anyway.
> Even gdb shows us the filename/tablename in backtraces. We are never
> going to be able to reproduce that.
Backtraces from *what*, exactly? 99% of the backend is still going
to be dealing with the same data as ever. It might be that poking
around in fd.c will be a little harder, but considering that fd.c
doesn't really know or care what the files it's manipulating are
anyway, I'm not convinced that this is a real issue.
> I guess I don't consider table schema commands inside transactions and
> such to be as big an items as the utility features we will need to
> build.
You've *got* to be kidding. We're constantly seeing complaints about
the fact that rolling back DROP or RENAME TABLE fails --- and worse,
leaves the table in a corrupted/inconsistent state. As far as I can
tell, that's one of the worst robustness problems we've got left to
fix. This is a big deal IMHO, and I want it to be fixed and fixed
right. I don't see how to fix it right if we try to keep physical
filenames tied to logical tablenames.
Moreover, that restriction will continue to hurt us if we try to
preserve it while implementing tablespaces, ANSI schemas, etc.
regards, tom lane
From pgsql-hackers-owner+M3397@hub.org Thu Jun 15 03:03:33 2000
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Date: Thu, 15 Jun 2000 16:56:12 +1000
From: Chris Bitmead <chrisb@nimrod.itg.telstra.com.au>
Organization: IBM Global Services
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To: "Ross J. Reedstrom" <reedstrm@rice.edu>
CC: PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: [HACKERS] Big 7.1 open items
References: <16985.961038832@sss.pgh.pa.us> <200006150321.XAA09510@candle.pha.pa.us> <20000615010312.A995@rice.edu>
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"Ross J. Reedstrom" wrote:
> Any strong objections to the mixed relname_oid solution? It gets us
> everything oids does, and still lets Bruce use 'ls -l' to find the big
> tables, putting off writing any admin tools that'll need to be rewritten,
> anyway.
Doesn't relname_oid defeat the purpose of oid file names, which is that
they don't change when the table is renamed? Wasn't it going to be oids
with a tool to create a symlink of relname -> oid ?
From pgsql-hackers-owner+M3400@hub.org Thu Jun 15 03:31:16 2000
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To: "Ross J. Reedstrom" <reedstrm@rice.edu>
cc: PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: [HACKERS] Big 7.1 open items
In-reply-to: <20000615010312.A995@rice.edu>
References: <16985.961038832@sss.pgh.pa.us> <200006150321.XAA09510@candle.pha.pa.us> <20000615010312.A995@rice.edu>
Comments: In-reply-to "Ross J. Reedstrom" <reedstrm@rice.edu>
message dated "Thu, 15 Jun 2000 01:03:12 -0500"
Date: Thu, 15 Jun 2000 03:11:52 -0400
Message-ID: <18798.961053112@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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"Ross J. Reedstrom" <reedstrm@rice.edu> writes:
> Any strong objections to the mixed relname_oid solution?
Yes!
You cannot make it work reliably unless the relname part is the original
relname and does not track ALTER TABLE RENAME. IMHO having an obsolete
relname in the filename is worse than not having the relname at all;
it's a recipe for confusion, it means you still need admin tools to tell
which end is really up, and what's worst is you might think you don't.
Furthermore it requires an additional column in pg_class to keep track
of the original relname, which is a waste of space and effort.
It also creates a portability risk, or at least fails to remove one,
since you are critically dependent on the assumption that the OS
supports long filenames --- on a filesystem that truncates names to less
than about 45 characters you're in very deep trouble. An OID-only
approach still works on traditional 14-char-filename Unix filesystems
(it'd mostly even work on DOS 8+3, though I doubt we care about that).
Finally, one of the reasons I want to go to filenames based only on OID
is that that'll make life easier for mdblindwrt. Original relname + OID
doesn't help, in fact it makes life harder (more shmem space needed to
keep track of the filename for each buffer).
Can we *PLEASE JUST LET GO* of this bad idea? No relname in the
filename. Period.
regards, tom lane
From tgl@sss.pgh.pa.us Thu Jun 15 03:31:11 2000
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To: Bruce Momjian <pgman@candle.pha.pa.us>
cc: Jan Wieck <JanWieck@Yahoo.com>, Oliver Elphick <olly@lfix.co.uk>,
PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: [HACKERS] Big 7.1 open items
In-reply-to: <200006150321.XAA09510@candle.pha.pa.us>
References: <200006150321.XAA09510@candle.pha.pa.us>
Comments: In-reply-to Bruce Momjian <pgman@candle.pha.pa.us>
message dated "Wed, 14 Jun 2000 23:21:15 -0400"
Date: Thu, 15 Jun 2000 03:14:30 -0400
Message-ID: <18830.961053270@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
Status: RO
Bruce Momjian <pgman@candle.pha.pa.us> writes:
> Well, we did have someone do a test implementation of oid file names,
> and their report was that is looked pretty ugly. However, if people are
> convinced it has to be done, we can get started. I guess I was waiting
> for Vadim's storage manager, where the whole idea of separate files is
> going to go away anyway, I suspect. We would then have to re-write all
> our admin tools for the new format.
I seem to recall him saying that he wanted to go to filename == OID
just like I'm suggesting. But I agree we probably ought to hold off
doing anything until he gets back from Russia and can let us know
whether that's still his plan. If he is planning one-huge-file or
something like that, we might as well let these issues go unfixed
for one more release cycle.
regards, tom lane
From pgsql-hackers-owner+M3401@hub.org Thu Jun 15 03:31:15 2000
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To: Bruce Momjian <pgman@candle.pha.pa.us>
cc: Jan Wieck <JanWieck@Yahoo.com>, Oliver Elphick <olly@lfix.co.uk>,
PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: [HACKERS] Big 7.1 open items
In-reply-to: <200006150321.XAA09510@candle.pha.pa.us>
References: <200006150321.XAA09510@candle.pha.pa.us>
Comments: In-reply-to Bruce Momjian <pgman@candle.pha.pa.us>
message dated "Wed, 14 Jun 2000 23:21:15 -0400"
Date: Thu, 15 Jun 2000 03:14:30 -0400
Message-ID: <18830.961053270@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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Bruce Momjian <pgman@candle.pha.pa.us> writes:
> Well, we did have someone do a test implementation of oid file names,
> and their report was that is looked pretty ugly. However, if people are
> convinced it has to be done, we can get started. I guess I was waiting
> for Vadim's storage manager, where the whole idea of separate files is
> going to go away anyway, I suspect. We would then have to re-write all
> our admin tools for the new format.
I seem to recall him saying that he wanted to go to filename == OID
just like I'm suggesting. But I agree we probably ought to hold off
doing anything until he gets back from Russia and can let us know
whether that's still his plan. If he is planning one-huge-file or
something like that, we might as well let these issues go unfixed
for one more release cycle.
regards, tom lane
From ZeugswetterA@wien.spardat.at Thu Jun 15 03:30:59 2000
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From: Zeugswetter Andreas SB <ZeugswetterA@wien.spardat.at>
To: "'Tom Lane'" <tgl@sss.pgh.pa.us>, Bruce Momjian <pgman@candle.pha.pa.us>
Cc: Jan Wieck <JanWieck@Yahoo.com>, Oliver Elphick <olly@lfix.co.uk>,
PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: AW: [HACKERS] Big 7.1 open items
Date: Thu, 15 Jun 2000 09:31:11 +0200
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Status: RO
> Bruce Momjian <pgman@candle.pha.pa.us> writes:
> > You need something that works from the command line, and
> something that
> > works if PostgreSQL is not running. How would you restore
> one file from
> > a tape.
>
> "Restore one file from a tape"? How are you going to do that anyway?
> You can't save and restore portions of a database like that, because
> of transaction commit status problems. To restore table X correctly,
> you'd have to restore pg_log as well, and then your other tables are
> hosed --- unless you also restore all of them from the backup. Only
> a complete database restore from tape would work, and for that you
> don't need to tell which file is which. So the above argument is a
> red herring.
>From what I know it is possible to simply restore one table file
since pg_log keeps all tid's. Of course it cannot guarantee integrity
and does not work if the table was altered.
> I realize it's nice to be able to tell which table file is which by
> eyeball, but the price we are paying for that small convenience is
> just too high. Give that up, and we can have rollbackable DROP and
> RENAME now (I'll personally commit to making it happen for 7.1).
> Continue to insist on it, and I don't think we'll *ever* have those
> features in a really robust form. It's just not possible to do
> multiple file renames atomically.
In the last proposal Bruce and I had it all layed out for tabname + oid
with no overhead in the normal situation, and little overhead if a rename
table crashed or was not rolled back or committed properly
which imho had all advantages combined.
Andreas
From ZeugswetterA@wien.spardat.at Thu Jun 15 04:31:04 2000
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From: Zeugswetter Andreas SB <ZeugswetterA@wien.spardat.at>
To: "'Don Baccus'" <dhogaza@pacifier.com>,
Bruce Momjian
<pgman@candle.pha.pa.us>, Tom Lane <tgl@sss.pgh.pa.us>
Cc: Jan Wieck <JanWieck@yahoo.com>, Oliver Elphick <olly@lfix.co.uk>,
PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: AW: [HACKERS] Big 7.1 open items
Date: Thu, 15 Jun 2000 10:04:51 +0200
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Status: RO
> In reality, very few people are going to be interested in restoring
> a table in a way that breaks referential integrity and other
> normal assumptions about what exists in the database.
This is not true. In my DBA history it would have saved me manweeks
of work if an easy and efficient restore of one single table from backup
would have been available in Informix and Oracle.
We allways had to restore most of the whole system to another machine only
to get back at some table info that would then be manually re-added
to the production system.
A restore of one table to a different/new tablename would have been
very convenient, and this is currently possible in PostgreSQL.
(create new table with same schema, then replace new table data file
with file from backup)
> The reality
> is that most people are going to engage in a little time travel
> to a past, consistent backup rather than do as you suggest.
No, this is what is done most of the time, but it is very inconvenient
to tell people that they loose all work from past days, so it is usually
done as I noted above if possible. We once had a situation where all data
was deleted from a table, but the problem was only noticed 3 weeks later.
> This is going to be more and more true as Postgres gains more and
> more acceptance in (no offense intended) the real world.
>
> >Right now, we use 'ps' with args to display backend
> information, and ls
> >-l to show disk information. We are going to lose that here.
>
> Dependence on "ls -l" is, IMO, a very weak argument.
In normal situations where everything works I agree, it is the
error situations where it really helps if you see what data is where.
debugging, lsof, Bruce already named them.
Andreas
From pgsql-hackers-owner+M3405@hub.org Thu Jun 15 04:31:09 2000
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From: Zeugswetter Andreas SB <ZeugswetterA@wien.spardat.at>
To: "'Tom Lane'" <tgl@sss.pgh.pa.us>,
"Ross J. Reedstrom"
<reedstrm@rice.edu>
Cc: PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: AW: [HACKERS] Big 7.1 open items
Date: Thu, 15 Jun 2000 10:26:12 +0200
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> "Ross J. Reedstrom" <reedstrm@rice.edu> writes:
> > Any strong objections to the mixed relname_oid solution?
>
> Yes!
>
> You cannot make it work reliably unless the relname part is
> the original
> relname and does not track ALTER TABLE RENAME.
It does, or should at least. Only problem case is where db crashes during
alter or commit/rollback. This could be fixed by first open that fails to
find the file
or vacuum, or some other utility.
> IMHO having
> an obsolete
> relname in the filename is worse than not having the relname at all;
> it's a recipe for confusion, it means you still need admin
> tools to tell
> which end is really up, and what's worst is you might think you don't.
>
> Furthermore it requires an additional column in pg_class to keep track
> of the original relname, which is a waste of space and effort.
it does not.
> Finally, one of the reasons I want to go to filenames based
> only on OID
> is that that'll make life easier for mdblindwrt. Original
> relname + OID
> doesn't help, in fact it makes life harder (more shmem space needed to
> keep track of the filename for each buffer).
I do not see this. filename is constructed from relname+oid.
if not found, do directory scan for *_<OID>.dat, if found --> rename.
Andreas
From pgsql-hackers-owner+M3407@hub.org Thu Jun 15 05:01:03 2000
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From: Zeugswetter Andreas SB <ZeugswetterA@wien.spardat.at>
To: "'Tom Lane'" <tgl@sss.pgh.pa.us>
Cc: PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: AW: [HACKERS] Big 7.1 open items
Date: Thu, 15 Jun 2000 10:41:50 +0200
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> It's just not possible to do
> multiple file renames atomically.
This is not necessary, since *_<OID> is unique regardless of relname prefix.
Andreas
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From: The Hermit Hacker <scrappy@hub.org>
To: Bruce Momjian <pgman@candle.pha.pa.us>
cc: Tom Lane <tgl@sss.pgh.pa.us>, Jan Wieck <JanWieck@Yahoo.com>,
Oliver Elphick <olly@lfix.co.uk>,
PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: [HACKERS] Big 7.1 open items
In-Reply-To: <200006150321.XAA09510@candle.pha.pa.us>
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On Wed, 14 Jun 2000, Bruce Momjian wrote:
> > Backtraces from *what*, exactly? 99% of the backend is still going
> > to be dealing with the same data as ever. It might be that poking
> > around in fd.c will be a little harder, but considering that fd.c
> > doesn't really know or care what the files it's manipulating are
> > anyway, I'm not convinced that this is a real issue.
>
> I was just throwing gdb out as an example. The bigger ones are ls,
> lsof/fstat, and tar.
You've lost me on this one ... if someone does an lsof of the process, it
will still provide them a list of open files ... are you complaining about
the extra step required to translate the file name to a "valid table"?
Oh, one point here ... this whole 'filenaming issue' ... as far as ls is
concerned, at least, only affects the superuser, since he's the only one
that can go 'ls'ng around i nthe directories ...
And, ummm, how hard would it be to have \d in psql display the "physical
table name" as part of its output?
Slight tangent here:
One thing that I think would be great if we could add is some sort of:
SELECT db_name, disk_space;
query wher a database owner, not the superuser, could see how much disk
space their tables are using up ... possible?
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To: "Ross J. Reedstrom" <reedstrm@rice.edu>
CC: PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: [HACKERS] Big 7.1 open items
References: <16985.961038832@sss.pgh.pa.us> <200006150321.XAA09510@candle.pha.pa.us> <20000615010312.A995@rice.edu>
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Ross J. Reedstrom wrote:
>
> Any strong objections to the mixed relname_oid solution? It gets us
> everything oids does, and still lets Bruce use 'ls -l' to find the big
> tables, putting off writing any admin tools that'll need to be rewritten,
> anyway.
I would object to the mixed name.
Consider:
CREATE TABLE FOO ....
ALTER TABLE FOO RENAME FOO_OLD;
CREATE TABLE FOO ....
For the same atomicity reason, rename can't change the
name of the files. So, which foo_<oid> is the FOO_OLD
and which is FOO?
In other words, in the presence of rename, putting
relname in the filename is misleading at best.
--
Mark Hollomon
mhh@nortelnetworks.com
ESN 451-9008 (302)454-9008
From pgsql-hackers-owner+M3413@hub.org Thu Jun 15 08:30:47 2000
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Then <tgl@sss.pgh.pa.us> spoke up and said:
> Precedence: bulk
>
> Bruce Momjian <pgman@candle.pha.pa.us> writes:
> > But seriously, let me give some background. I used Ingres, that used
> > the VMS file system, but used strange sequential AAAF324 numbers for
> > tables. When someone deleted a table, or we were looking at what tables
> > were using disk space, it was impossible to find the Ingres table names
> > that went with the file. There was a system table that showed it, but
> > it was poorly documented, and if you deleted the table, there was no way
> > to look on the tape to find out which file to restore.
>
> Fair enough, but it seems to me that the answer is to expend some effort
> on system admin support tools. We could do a lot in that line with less
> effort than trying to make a fundamentally mismatched filesystem
> representation do what we need.
We've been an Ingres shop as long as there's been an Ingres. While
we've also had the problem Bruce noticed with table names, we've
*also* used the trivial fix of running a (simple) Report Writer job
each night, immediately before the backup, that lists all of the
database tables/indicies and the underlying files.
True, if someone drops/recreates a table twice between backups we
can't find the intermediate file name, but since we also haven't
backed up that filename, this isn't an issue.
Also, the consistency issue is really not as important as you would
think. If you are restoring a table, you want the information in it,
whether or not it's consistent with anything else. I've done hundreds
of table restores (can you say "modify table to heap"?) and never once
has inconsistency been an issue. Oh, yeah, and we don't shut the
database down for this, either. (That last isn't my choice, BTW.)
--
=====================================================================
| JAVA must have been developed in the wilds of West Virginia. |
| After all, why else would it support only single inheritance?? |
=====================================================================
| Finger geek@cmu.edu for my public key. |
=====================================================================
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From dhogaza@pacifier.com Thu Jun 15 09:31:05 2000
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Date: Thu, 15 Jun 2000 05:40:49 -0700
To: Zeugswetter Andreas SB <ZeugswetterA@wien.spardat.at>,
Bruce Momjian <pgman@candle.pha.pa.us>, Tom Lane <tgl@sss.pgh.pa.us>
From: Don Baccus <dhogaza@pacifier.com>
Subject: Re: AW: [HACKERS] Big 7.1 open items
Cc: Jan Wieck <JanWieck@yahoo.com>, Oliver Elphick <olly@lfix.co.uk>,
PostgreSQL-development <pgsql-hackers@postgresql.org>
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At 10:04 AM 6/15/00 +0200, Zeugswetter Andreas SB wrote:
>
>> In reality, very few people are going to be interested in restoring
>> a table in a way that breaks referential integrity and other
>> normal assumptions about what exists in the database.
>
>This is not true. In my DBA history it would have saved me manweeks
>of work if an easy and efficient restore of one single table from backup
>would have been available in Informix and Oracle.
>We allways had to restore most of the whole system to another machine only
>to get back at some table info that would then be manually re-added
>to the production system.
I'm missing something, I guess. You would do a createdb, do a filesystem
copy of pg_log and one file into it, and then read data from the table
without having to restore the other tables in the database?
I'm just curious - when was the last time you restored a Postgres
database in this piecemeal manner, and how often do you do it?
- Don Baccus, Portland OR <dhogaza@pacifier.com>
Nature photos, on-line guides, Pacific Northwest
Rare Bird Alert Service and other goodies at
http://donb.photo.net.
From pgsql-hackers-owner+M3440@hub.org Thu Jun 15 14:46:22 2000
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Date: Thu, 15 Jun 2000 11:45:19 -0500
From: "Ross J. Reedstrom" <reedstrm@rice.edu>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: PostgreSQL-development <pgsql-hackers@postgreSQL.org>
Subject: Re: [HACKERS] Big 7.1 open items
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On Thu, Jun 15, 2000 at 03:11:52AM -0400, Tom Lane wrote:
> "Ross J. Reedstrom" <reedstrm@rice.edu> writes:
> > Any strong objections to the mixed relname_oid solution?
>
> Yes!
>
> You cannot make it work reliably unless the relname part is the original
> relname and does not track ALTER TABLE RENAME. IMHO having an obsolete
> relname in the filename is worse than not having the relname at all;
> it's a recipe for confusion, it means you still need admin tools to tell
> which end is really up, and what's worst is you might think you don't.
The plan here was to let VACUUM handle renaming the file, since it
will already have all the necessary locks. This shortens the window
of confusion. ALTER TABLE RENAME doesn't happen that often, really -
the relname is there just for human consumption, then.
>
> Furthermore it requires an additional column in pg_class to keep track
> of the original relname, which is a waste of space and effort.
>
I actually started down this path thinking about implementing SCHEMA,
since tables in the same DB but in different schema can have the same
relname, I figured I needed to change that. We'll need something in
pg_class to keep track of what schema a relation is in, instead.
> It also creates a portability risk, or at least fails to remove one,
> since you are critically dependent on the assumption that the OS
> supports long filenames --- on a filesystem that truncates names to less
> than about 45 characters you're in very deep trouble. An OID-only
> approach still works on traditional 14-char-filename Unix filesystems
> (it'd mostly even work on DOS 8+3, though I doubt we care about that).
Actually, no. Since I store the filename in a name attribute, I used this
nifty function somebody wrote, makeObjectName, to trim the relname part,
but leave the oid. (Yes, I know it's yours ;-)
>
> Finally, one of the reasons I want to go to filenames based only on OID
> is that that'll make life easier for mdblindwrt. Original relname + OID
> doesn't help, in fact it makes life harder (more shmem space needed to
> keep track of the filename for each buffer).
Can you explain in more detail how this helps? Not by letting the bufmgr
know that oid == filename, I hope. We need to improving the abstraction
of the smgr, not add another violation. Ah, sorry, mdblindwrt _is_
in the smgr.
Hmm, grovelling through that code, I see how it could be simpler if reloid
== filename. Heck, we even get to save shmem in the buffdesc.blind part,
since we only need the dbname in there, now.
Hmm, I see I missed the relpath_blind() in my patch - oops. (relpath()
is always called with RelationGetPhysicalRelationName(), and that's
where I was putting in the relphysname)
Hmm, what's all this with functions in catalog.c that are only called by
smgr/md.c? seems to me that anything having to do with physical storage
(like the path!) belongs in the smgr abstraction.
>
> Can we *PLEASE JUST LET GO* of this bad idea? No relname in the
> filename. Period.
>
Gee, so dogmatic. No one besides Bruce and Hiroshi discussed this _at
all_ when I first put up patches two month ago. O.K., I'll do the oids
only version (and fix up relpath_blind)
Ross
--
Ross J. Reedstrom, Ph.D., <reedstrm@rice.edu>
NSBRI Research Scientist/Programmer
Computer and Information Technology Institute
Rice University, 6100 S. Main St., Houston, TX 77005
From Inoue@tpf.co.jp Thu Jun 15 17:45:40 2000
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From: "Hiroshi Inoue" <Inoue@tpf.co.jp>
To: "Bruce Momjian" <pgman@candle.pha.pa.us>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Cc: "Tom Lane" <tgl@sss.pgh.pa.us>,
"PostgreSQL-development" <pgsql-hackers@postgreSQL.org>
Subject: RE: [HACKERS] Big 7.1 open items
Date: Fri, 16 Jun 2000 06:48:21 +0900
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> -----Original Message-----
> From: pgsql-hackers-owner@hub.org
> [mailto:pgsql-hackers-owner@hub.org]On Behalf Of Bruce Momjian
>
> > > Can we *PLEASE JUST LET GO* of this bad idea? No relname in the
> > > filename. Period.
> > >
> >
> > Gee, so dogmatic. No one besides Bruce and Hiroshi discussed this _at
> > all_ when I first put up patches two month ago. O.K., I'll do the oids
> > only version (and fix up relpath_blind)
>
> Hold on. I don't think we want that work done yet. Seems even Tom is
> thinking that if Vadim is going to re-do everything later anyway, we may
> be better with a relname/oid solution that does require additional
> administration apps.
>
Hmm,why is naming rule first ?
I've never enphasized naming rule except that it should be unique.
It has been my main point to reduce the necessity of naming rule
as possible. IIRC,by keeping the stored place in pg_class,Ross's
trial patch remains only 2 places where naming rule is required.
So wouldn't we be free from naming rule(it would not be so difficult
to change naming rule if the rule is found to be bad) ?
I've also mentioned many times neither relname nor oid is sufficient
for the uniqueness. In addiiton neither relname nor oid would be
necessary for the uniqueness.
IMHO,it's bad to rely on the item which is neither necessary nor
sufficient.
I proposed relname+unique_id naming once. The unique_id is
independent from oid. The relname is only for convinience for
DBA and so we don't have to change it due to RENAME.
Db's consistency is much more important than dba's satis-
faction.
Comments ?
Regards.
Hiroshi Inoue
Inoue@tpf.co.jp
From pgsql-hackers-owner+M3448@hub.org Thu Jun 15 19:01:03 2000
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Date: Thu, 15 Jun 2000 17:53:59 -0500
From: "Ross J. Reedstrom" <reedstrm@rice.edu>
To: PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: [HACKERS] Big 7.1 open items
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On Thu, Jun 15, 2000 at 05:48:59PM -0400, Bruce Momjian wrote:
> > I've also mentioned many times neither relname nor oid is sufficient
> > for the uniqueness. In addiiton neither relname nor oid would be
> > necessary for the uniqueness.
> > IMHO,it's bad to rely on the item which is neither necessary nor
> > sufficient.
> > I proposed relname+unique_id naming once. The unique_id is
> > independent from oid. The relname is only for convinience for
> > DBA and so we don't have to change it due to RENAME.
> > Db's consistency is much more important than dba's satis-
> > faction.
> >
> > Comments ?
>
> I am happy not to rename the file on 'RENAME', but seems no one likes
> that.
Good, 'cause that's how I've implemented it so far. Actually, all
I've done is port my previous patch to current, with one little
change: I added a macro RelationGetRealRelationName which does what
RelationGetPhysicalRelationName used to do: i.e. return the relname with
no temptable funny business, and used that for the relcache macros. It
passes all the serial regression tests: I haven't run the parallel tests
yet. ALTER TABLE RENAME rollsback nicely. I'll need to learn some omre
about xacts to get DROP TABLE rolling back.
I'll drop it on PATCHES right now, for comment.
Ross
--
Ross J. Reedstrom, Ph.D., <reedstrm@rice.edu>
NSBRI Research Scientist/Programmer
Computer and Information Technology Institute
Rice University, 6100 S. Main St., Houston, TX 77005
From pgsql-hackers-owner+M3451@hub.org Thu Jun 15 20:01:00 2000
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To: "Ross J. Reedstrom" <reedstrm@rice.edu>
cc: PostgreSQL-development <pgsql-hackers@postgreSQL.org>
Subject: Re: [HACKERS] Big 7.1 open items
In-reply-to: <20000615114519.B3939@rice.edu>
References: <16985.961038832@sss.pgh.pa.us> <200006150321.XAA09510@candle.pha.pa.us> <20000615010312.A995@rice.edu> <18798.961053112@sss.pgh.pa.us> <20000615114519.B3939@rice.edu>
Comments: In-reply-to "Ross J. Reedstrom" <reedstrm@rice.edu>
message dated "Thu, 15 Jun 2000 11:45:19 -0500"
Date: Thu, 15 Jun 2000 19:53:52 -0400
Message-ID: <2260.961113232@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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"Ross J. Reedstrom" <reedstrm@rice.edu> writes:
> On Thu, Jun 15, 2000 at 03:11:52AM -0400, Tom Lane wrote:
>> "Ross J. Reedstrom" <reedstrm@rice.edu> writes:
>>>> Any strong objections to the mixed relname_oid solution?
>>
>> Yes!
> The plan here was to let VACUUM handle renaming the file, since it
> will already have all the necessary locks. This shortens the window
> of confusion. ALTER TABLE RENAME doesn't happen that often, really -
> the relname is there just for human consumption, then.
Yeah, I've seen tons of discussion of how if we do this, that, and
the other thing, and be prepared to fix up some other things in case
of crash recovery, we can make it work with filename == relname + OID
(where relname tracks logical name, at least at some remove).
Probably. Assuming nobody forgets anything.
I'm just trying to point out that that's a huge amount of pretty
delicate mechanism. The amount of work required to make it trustworthy
looks to me to dwarf the admin tools that Bruce is complaining about.
And we only have a few people competent to do the work. (With all
due respect, Ross, if you weren't already aware of the implications
for mdblindwrt, I have to wonder what else you missed.)
Filename == OID is so simple, reliable, and straightforward by
comparison that I think the decision is a no-brainer.
If we could afford to sink unlimited time into this one issue then
it might make sense to do it the hard way, but we have enough
important stuff on our TODO list to keep us all busy for years ---
I cannot believe that it's an effective use of our time to do this.
> Hmm, what's all this with functions in catalog.c that are only called by
> smgr/md.c? seems to me that anything having to do with physical storage
> (like the path!) belongs in the smgr abstraction.
Yeah, there's a bunch of stuff that should have been implemented by
adding new smgr entry points, but wasn't. It should be pushed down.
(I can't resist pointing out that one of those things is physical
relation rename, which will go away and not *need* to be pushed down
if we do it the way I want.)
regards, tom lane
From tgl@sss.pgh.pa.us Thu Jun 15 20:00:59 2000
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To: Bruce Momjian <pgman@candle.pha.pa.us>
cc: "Ross J. Reedstrom" <reedstrm@rice.edu>,
PostgreSQL-development <pgsql-hackers@postgreSQL.org>
Subject: Re: [HACKERS] Big 7.1 open items
In-reply-to: <200006151935.PAA17512@candle.pha.pa.us>
References: <200006151935.PAA17512@candle.pha.pa.us>
Comments: In-reply-to Bruce Momjian <pgman@candle.pha.pa.us>
message dated "Thu, 15 Jun 2000 15:35:45 -0400"
Date: Thu, 15 Jun 2000 19:57:05 -0400
Message-ID: <2280.961113425@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
Status: RO
Bruce Momjian <pgman@candle.pha.pa.us> writes:
>> Gee, so dogmatic. No one besides Bruce and Hiroshi discussed this _at
>> all_ when I first put up patches two month ago. O.K., I'll do the oids
>> only version (and fix up relpath_blind)
> Hold on. I don't think we want that work done yet. Seems even Tom is
> thinking that if Vadim is going to re-do everything later anyway, we may
> be better with a relname/oid solution that does require additional
> administration apps.
Don't put words in my mouth, please. If we are going to throw the
work away later, it'd be foolish to do the much greater amount of
work needed to make filename=relname+OID fly than is needed for
filename=OID.
However, I'm pretty sure I recall Vadim stating that he thought
filename=OID would be required for his smgr changes anyway...
regards, tom lane
From pgsql-hackers-owner+M3453@hub.org Thu Jun 15 21:01:01 2000
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From: "Hiroshi Inoue" <Inoue@tpf.co.jp>
To: "Bruce Momjian" <maillist@candle.pha.pa.us>,
"Tom Lane" <tgl@sss.pgh.pa.us>
Cc: "PostgreSQL-development" <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: RE: [HACKERS] Big 7.1 open items
Date: Fri, 16 Jun 2000 09:28:14 +0900
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> -----Original Message-----
> From: pgsql-hackers-owner@hub.org [mailto:pgsql-hackers-owner@hub.org]On
> Behalf Of Tom Lane
>
> "Ross J. Reedstrom" <reedstrm@rice.edu> writes:
> > On Thu, Jun 15, 2000 at 03:11:52AM -0400, Tom Lane wrote:
> >> "Ross J. Reedstrom" <reedstrm@rice.edu> writes:
> >>>> Any strong objections to the mixed relname_oid solution?
> >>
> >> Yes!
>
> > The plan here was to let VACUUM handle renaming the file, since it
> > will already have all the necessary locks. This shortens the window
> > of confusion. ALTER TABLE RENAME doesn't happen that often, really -
> > the relname is there just for human consumption, then.
>
> Yeah, I've seen tons of discussion of how if we do this, that, and
> the other thing, and be prepared to fix up some other things in case
> of crash recovery, we can make it work with filename == relname + OID
> (where relname tracks logical name, at least at some remove).
>
I've seen little discussion of how to avoid the use of naming rule.
I've proposed many times that we should keep the information
where the table is stored in our database itself. I've never seen
clear objections to it. So I could understand my proposal is OK ?
Isn't it much more important than naming rule ? Under the
mechanism,we could easily replace bad naming rule.
And I believe that Ross's work is mostly around the mechanism
not naming rule.
Now I like neither relname nor oid because it's not sufficient
for my purpose.
Regards.
Hiroshi Inoue
Inoue@tpf.co.jp
From tgl@sss.pgh.pa.us Thu Jun 15 22:01:02 2000
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To: "Hiroshi Inoue" <Inoue@tpf.co.jp>
cc: "Bruce Momjian" <maillist@candle.pha.pa.us>,
"PostgreSQL-development" <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: Re: [HACKERS] Big 7.1 open items
In-reply-to: <000d01bfd729$c24b29c0$2801007e@tpf.co.jp>
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Comments: In-reply-to "Hiroshi Inoue" <Inoue@tpf.co.jp>
message dated "Fri, 16 Jun 2000 09:28:14 +0900"
Date: Thu, 15 Jun 2000 21:57:27 -0400
Message-ID: <2727.961120647@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
Status: ROr
"Hiroshi Inoue" <Inoue@tpf.co.jp> writes:
> Now I like neither relname nor oid because it's not sufficient
> for my purpose.
We should probably not do much of anything with this issue until
we have a clearer understanding of what we want to do about
tablespaces and schemas.
My gut feeling is that we will end up with pathnames that look
something like
.../data/base/DBNAME/TABLESPACE/OIDOFRELATION
(with .N attached if a segment of a large relation, of course).
The TABLESPACE "name" should likely be an OID itself, but it wouldn't
have to be if you are willing to say that tablespaces aren't renamable.
(Come to think of it, does anyone care about being able to rename
databases? ;-)) Note that the TABLESPACE will often be a symlink
to storage on another drive, rather than a plain subdirectory of the
DBNAME, but that shouldn't be an issue at this level of discussion.
I think that schemas probably don't enter into this. We should instead
rely on the uniqueness of OIDs to prevent filename collisions. However,
OIDs aren't really unique: different databases in an installation will
use the same OIDs for their system tables. My feeling is that we can
live with a restriction like "you can't store the system tables of
different databases in the same tablespace". Alternatively we could
avoid that issue by inverting the pathname order:
.../data/base/TABLESPACE/DBNAME/OIDOFRELATION
Note that in any case, system tables will have to live in a
predetermined tablespace, since you can't very well look in pg_class
to find out which tablespace pg_class lives in. Perhaps we should
just reserve a tablespace per database for system tables and forget
the whole issue. If we do that, there's not really any need for
the database in the path! Just
.../data/base/TABLESPACE/OIDOFRELATION
would do fine and help reduce lookup overhead.
BTW, schemas do make things interesting for the other camp:
is it possible for the same table to be referenced by different
names in different schemas? If so, just how useful is it to pick
one of those names arbitrarily for the filename? This is an advanced
version of the main objection to using the original relname and not
updating it at RENAME TABLE --- sooner or later, the filenames are
going to be more confusing than helpful.
Comments? Have I missed something important about schemas?
regards, tom lane
From pgsql-hackers-owner+M3457@hub.org Thu Jun 15 22:27:45 2000
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From: Bruce Momjian <pgman@candle.pha.pa.us>
Message-Id: <200006160224.WAA04345@candle.pha.pa.us>
Subject: Re: [HACKERS] Big 7.1 open items
In-Reply-To: <2727.961120647@sss.pgh.pa.us> "from Tom Lane at Jun 15, 2000 09:57:27
pm"
To: Tom Lane <tgl@sss.pgh.pa.us>
Date: Thu, 15 Jun 2000 22:24:52 -0400 (EDT)
CC: Hiroshi Inoue <Inoue@tpf.co.jp>, Bruce Momjian <maillist@candle.pha.pa.us>,
PostgreSQL-development <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
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> "Hiroshi Inoue" <Inoue@tpf.co.jp> writes:
> > Now I like neither relname nor oid because it's not sufficient
> > for my purpose.
>
> We should probably not do much of anything with this issue until
> we have a clearer understanding of what we want to do about
> tablespaces and schemas.
Here is an analysis of our options:
Work required Disadvantages
----------------------------------------------------------------------------
Keep current system no work rename/create no rollback
relname/oid but less work new pg_class column,
no rename change filename not accurate on
rename
relname/oid with more work complex code
rename change during
vacuum
oid filename less work, but confusing to admins
need admin tools
--
Bruce Momjian | http://www.op.net/~candle
pgman@candle.pha.pa.us | (610) 853-3000
+ If your life is a hard drive, | 830 Blythe Avenue
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026
From Inoue@tpf.co.jp Thu Jun 15 22:41:50 2000
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From: "Hiroshi Inoue" <Inoue@tpf.co.jp>
To: "Tom Lane" <tgl@sss.pgh.pa.us>
Cc: "Bruce Momjian" <maillist@candle.pha.pa.us>,
"PostgreSQL-development" <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: RE: [HACKERS] Big 7.1 open items
Date: Fri, 16 Jun 2000 11:43:52 +0900
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Sorry for my previous mail. It was posted by my mistake.
> -----Original Message-----
> From: Tom Lane [mailto:tgl@sss.pgh.pa.us]
>
> "Hiroshi Inoue" <Inoue@tpf.co.jp> writes:
> > Now I like neither relname nor oid because it's not sufficient
> > for my purpose.
>
> We should probably not do much of anything with this issue until
> we have a clearer understanding of what we want to do about
> tablespaces and schemas.
>
> My gut feeling is that we will end up with pathnames that look
> something like
>
> .../data/base/DBNAME/TABLESPACE/OIDOFRELATION
>
Schema is a logical concept and irrevant to physical location.
I strongly object your suggestion unless above means *default*
location.
Tablespace is an encapsulation of table allocation and the
name should be irrevant to the location basically. So above
seems very bad for me.
Anyway I don't see any advantage in fixed mapping impleme
ntation. After renewal,we should at least have a possibility to
allocate a specific table in arbitrary separate directory.
Regards.
Hiroshi Inoue
Inoue@tpf.co.jp
From Inoue@tpf.co.jp Thu Jun 15 23:31:00 2000
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From: "Hiroshi Inoue" <Inoue@tpf.co.jp>
To: "Bruce Momjian" <pgman@candle.pha.pa.us>, "Tom Lane" <tgl@sss.pgh.pa.us>
Cc: "Bruce Momjian" <maillist@candle.pha.pa.us>,
"PostgreSQL-development" <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: RE: [HACKERS] Big 7.1 open items
Date: Fri, 16 Jun 2000 12:20:16 +0900
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> -----Original Message-----
> From: Bruce Momjian [mailto:pgman@candle.pha.pa.us]
>
> > "Hiroshi Inoue" <Inoue@tpf.co.jp> writes:
> > > Now I like neither relname nor oid because it's not sufficient
> > > for my purpose.
> >
> > We should probably not do much of anything with this issue until
> > we have a clearer understanding of what we want to do about
> > tablespaces and schemas.
>
> Here is an analysis of our options:
>
> Work required Disadvantages
> ------------------------------------------------------------------
> ----------
>
> Keep current system no work rename/create
> no rollback
>
> relname/oid but less work new pg_class column,
> no rename change filename not
> accurate on
> rename
>
> relname/oid with more work complex code
> rename change during
> vacuum
>
> oid filename less work, but confusing to admins
> need admin tools
>
Please add my opinion for naming rule.
relname/unique_id but need some work new pg_class column,
no relname change. for unique-id generation filename not relname
Regards.
Hiroshi Inoue
Inoue@tpf.co.jp
From pgsql-hackers-owner+M3465@hub.org Fri Jun 16 00:01:01 2000
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From: "Hiroshi Inoue" <Inoue@tpf.co.jp>
To: "Tom Lane" <tgl@sss.pgh.pa.us>
Cc: "PostgreSQL-development" <pgsql-hackers@postgresql.org>
Subject: RE: [HACKERS] Big 7.1 open items
Date: Fri, 16 Jun 2000 12:57:44 +0900
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> -----Original Message-----
> From: Tom Lane [mailto:tgl@sss.pgh.pa.us]
>
> "Hiroshi Inoue" <Inoue@tpf.co.jp> writes:
> > Please add my opinion for naming rule.
>
> > relname/unique_id but need some work new
> pg_class column,
> > no relname change. for unique-id generation filename not relname
>
> Why is a unique ID better than --- or even different from ---
> using the relation's OID? It seems pointless to me...
>
For example,in the implementation of CLUSTER command,
we would need another new file for the target relation in
order to put sorted rows but don't we want to change the
OID ? It would be needed for table re-construction generally.
If I remember correectly,you once proposed OID+version
naming for the cases.
Regards.
Hiroshi Inoue
Inoue@tpf.co.jp
From Inoue@tpf.co.jp Fri Jun 16 02:01:00 2000
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From: "Hiroshi Inoue" <Inoue@tpf.co.jp>
To: "Tom Lane" <tgl@sss.pgh.pa.us>
Cc: "Bruce Momjian" <maillist@candle.pha.pa.us>,
"PostgreSQL-development" <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: RE: [HACKERS] Big 7.1 open items
Date: Fri, 16 Jun 2000 14:35:21 +0900
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> -----Original Message-----
> From: Tom Lane [mailto:tgl@sss.pgh.pa.us]
>
> "Hiroshi Inoue" <Inoue@tpf.co.jp> writes:
> > Tablespace is an encapsulation of table allocation and the
> > name should be irrevant to the location basically. So above
> > seems very bad for me.
> > Anyway I don't see any advantage in fixed mapping impleme
> > ntation. After renewal,we should at least have a possibility to
> > allocate a specific table in arbitrary separate directory.
>
> Call a "directory" a "tablespace" and we're on the same page,
> aren't we? Actually I'd envision some kind of admin command
> "CREATE TABLESPACE foo AS /path/to/wherever".
Yes,I think 'tablespace -> directory' is the most natural
extension under current file_per_table storage manager.
If many_tables_in_a_file storage manager is introduced,we
may be able to change the definiiton of TABLESPACE
to 'tablespace -> files' like Oracle.
> That would make
> appropriate system catalog entries and also create a symlink
> from ".../data/base/foo" (or some such place) to the target
> directory.
> Then when we make a table in that tablespace,
> it's in the right place. Problem solved, no?
>
I don't like symlink for dbms data files. However it may
be OK,If symlink are limited to 'tablespace->directory'
corrspondence and all tablespaces(including default
etc) are symlink. It is simple and all debugging would
be processed under tablespace_is_symlink environment.
> It gets a little trickier if you want to be able to split
> multi-gig tables across several tablespaces, though, since
> you couldn't just append ".N" to the base table path in that
> scenario.
>
This seems to be not that easy to solve now.
Ross doesn't change this naming rule for multi-gig
tables either in his trial.
> I'd be interested to know what sort of facilities Oracle
> provides for managing huge tables...
>
In my knowledge about old Oracle,one TABLESPACE
could have many DATAFILEs which could contain
many tables.
Regards.
Hiroshi Inoue
Inoue@tpf.co.jp
From pgsql-hackers-owner+M3469@hub.org Fri Jun 16 02:01:03 2000
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To: "Hiroshi Inoue" <Inoue@tpf.co.jp>
cc: "PostgreSQL-development" <pgsql-hackers@postgresql.org>
Subject: Re: [HACKERS] Big 7.1 open items
In-reply-to: <000501bfd747$067f0220$2801007e@tpf.co.jp>
References: <000501bfd747$067f0220$2801007e@tpf.co.jp>
Comments: In-reply-to "Hiroshi Inoue" <Inoue@tpf.co.jp>
message dated "Fri, 16 Jun 2000 12:57:44 +0900"
Date: Fri, 16 Jun 2000 01:54:46 -0400
Message-ID: <5746.961134886@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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"Hiroshi Inoue" <Inoue@tpf.co.jp> writes:
>> Why is a unique ID better than --- or even different from ---
>> using the relation's OID? It seems pointless to me...
> For example,in the implementation of CLUSTER command,
> we would need another new file for the target relation in
> order to put sorted rows but don't we want to change the
> OID ? It would be needed for table re-construction generally.
> If I remember correectly,you once proposed OID+version
> naming for the cases.
Hmm, so you are thinking that the pg_class row for the table would
include this uniqueID, and then committing the pg_class update would
be the atomic action that replaces the old table contents with the
new? It does have some attraction now that I think about it.
But there are other ways we could do the same thing. If we want to
have tablespaces, there will need to be a tablespace identifier in
each pg_class row. So we could do CLUSTER in the same way as we'd
move a table from one tablespace to another: create the new files in
the new tablespace directory, and the commit of the new pg_class row
with the new tablespace value is the atomic action that makes the new
files valid and the old files not.
You will probably say "but I didn't want to move my table to a new
tablespace just to cluster it!" I think we could live with that,
though. A tablespace doesn't need to have any existence more concrete
than a subdirectory, in my vision of the way things would work. We
could do something like making two subdirectories of each place that
the dbadmin designates as a "tablespace", so that we make two logical
tablespaces out of what the dbadmin thinks of as one. Then we can
ping-pong between those directories to do things like clustering "in
place".
Basically I want to keep the bottom-level mechanisms as simple and
reliable as we possibly can. The fewer concepts are known down at
the bottom, the better. If we can keep the pathname constituents
to just "tablespace" and "relation OID" we'll be in great shape ---
but each additional concept that has to be known down there is
another potential problem.
regards, tom lane
From pgsql-hackers-owner+M3471@hub.org Fri Jun 16 03:31:05 2000
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From: "Hiroshi Inoue" <Inoue@tpf.co.jp>
To: "Tom Lane" <tgl@sss.pgh.pa.us>
Cc: "PostgreSQL-development" <pgsql-hackers@postgresql.org>
Subject: RE: [HACKERS] Big 7.1 open items
Date: Fri, 16 Jun 2000 16:03:06 +0900
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> -----Original Message-----
> From: Tom Lane [mailto:tgl@sss.pgh.pa.us]
>
> "Hiroshi Inoue" <Inoue@tpf.co.jp> writes:
> >> Why is a unique ID better than --- or even different from ---
> >> using the relation's OID? It seems pointless to me...
>
> > For example,in the implementation of CLUSTER command,
> > we would need another new file for the target relation in
> > order to put sorted rows but don't we want to change the
> > OID ? It would be needed for table re-construction generally.
> > If I remember correectly,you once proposed OID+version
> > naming for the cases.
>
> Hmm, so you are thinking that the pg_class row for the table would
> include this uniqueID,
No,I just include the place where the table is stored(pathname under
current file_per_table storage manager) in the pg_class row because
I don't want to rely on table allocating rule(naming rule for current)
to access existent relation files. This has always been my main point.
Many_tables_in_a_file storage manager wouldn't be able to live without
keeping this kind of infomation.
This information(where it is stored) is diffrent from tablespace(where
to store) information. There was an idea to keep the information into
opaque entry in pg_class which only a specific storage manager
could handle. There was an idea to have a new system table which
keeps the information. and so on...
> and then committing the pg_class update would
> be the atomic action that replaces the old table contents with the
> new? It does have some attraction now that I think about it.
>
> But there are other ways we could do the same thing. If we want to
> have tablespaces, there will need to be a tablespace identifier in
> each pg_class row. So we could do CLUSTER in the same way as we'd
> move a table from one tablespace to another: create the new files in
> the new tablespace directory, and the commit of the new pg_class row
> with the new tablespace value is the atomic action that makes the new
> files valid and the old files not.
>
> You will probably say "but I didn't want to move my table to a new
> tablespace just to cluster it!"
Yes.
> I think we could live with that,
> though. A tablespace doesn't need to have any existence more concrete
> than a subdirectory, in my vision of the way things would work. We
> could do something like making two subdirectories of each place that
> the dbadmin designates as a "tablespace", so that we make two logical
> tablespaces out of what the dbadmin thinks of as one.
Certainly we could design TABLESPACE(where to store) as above.
> Then we can
> ping-pong between those directories to do things like clustering "in
> place".
>
But maybe we must keep the directory information where the table was
*ping-ponged* in (e.g.) pg_class. Is such an implementation cleaner or
more extensible than mine(keeping the stored place exactly) ?
Regards.
Hiroshi Inoue
Inoue@tpf.co.jp
From pgsql-hackers-owner+M3473@hub.org Fri Jun 16 04:01:12 2000
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To: Chris Bitmead <chrisb@nimrod.itg.telstra.com.au>
cc: PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: [HACKERS] Big 7.1 open items
In-reply-to: <3949BCC4.8424A58F@nimrod.itg.telecom.com.au>
References: <200006142043.WAA07887@hot.jw.home> <16606.961034835@sss.pgh.pa.us> <3949BCC4.8424A58F@nimrod.itg.telecom.com.au>
Comments: In-reply-to Chris Bitmead <chrisb@nimrod.itg.telstra.com.au>
message dated "Fri, 16 Jun 2000 15:36:04 +1000"
Date: Fri, 16 Jun 2000 03:34:47 -0400
Message-ID: <6100.961140887@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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Chris Bitmead <chrisb@nimrod.itg.telstra.com.au> writes:
> Tom Lane wrote:
>> I don't see a lot of value in that. Better to do something like
>> tablespaces:
>>
>> <dbroot>/<oidoftablespace>/<oidofobject>
> What is the benefit of having oidoftablespace in the directory path?
> Isn't tablespace an idea so you can store it somewhere completely
> different?
> Or is there some symlink idea or something?
Exactly --- I'm assuming that the tablespace "directory" is likely
to be a symlink to some other mounted volume. The point here is
to keep the low-level file access routines from having to know very
much about tablespaces or file organization. In the above proposal,
all they need to know is the relation's OID and the name (or OID)
of the tablespace the relation's assigned to; then they can form
a valid path using a hardwired rule. There's still plenty of
flexibility of organization, but it's not necessary to know that
where the rubber meets the road (eg, when you're down inside mdblindwrt
trying to dump a dirty buffer to disk with no spare resources to find
out anything about the relation the page belongs to...)
regards, tom lane
From JanWieck@t-online.de Fri Jun 16 11:01:06 2000
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From: JanWieck@t-online.de (Jan Wieck)
Message-Id: <200006161242.OAA15163@hot.jw.home>
Subject: Re: [HACKERS] Big 7.1 open items
In-Reply-To: <3238.961126521@sss.pgh.pa.us> from Tom Lane at "Jun 15, 2000 11:35:21
pm"
To: Tom Lane <tgl@sss.pgh.pa.us>
Date: Fri, 16 Jun 2000 14:42:12 +0200 (MEST)
CC: Hiroshi Inoue <Inoue@tpf.co.jp>, Bruce Momjian <maillist@candle.pha.pa.us>,
PostgreSQL-development <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Reply-To: Jan Wieck <JanWieck@Yahoo.com>
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Status: ROr
Tom Lane wrote:
>
> It gets a little trickier if you want to be able to split
> multi-gig tables across several tablespaces, though, since
> you couldn't just append ".N" to the base table path in that
> scenario.
>
> I'd be interested to know what sort of facilities Oracle
> provides for managing huge tables...
Oracle tablespaces are a collection of 1...n preallocated
files. Each table then is bound to a tablespace and
allocates extents (chunks) from those files.
There are some per table attributes that control the extent
sizes with default values coming from the tablespace. The
initial extent size, the nextextent and the pctincrease.
There is a hardcoded limit for the number of extents a table
can have at all. In Oracle7 it was 512 (or somewhat below -
don't recall correct). Maybe that's gone with Oracle8, don't
know.
This storage concept has IMHO a couple of advatages over
ours.
The tablespace files are preallocated, so there will
never be a change in block allocation during runtime and
that's the base for fdatasync() beeing sufficient at
syncpoints. All what might be inaccurate after a crash is
the last modified time in the inode, and that's totally
irrelevant for Oracle. The fsck will never fail, and
anything is up to Oracle's recovery.
The number of total tablespace files is limited to a
value that ensures, that the backends can keep them all
open all the time. It's hard to exceed that limit. A
typical SAP installation with more than 20,000
tables/indices doesn't need more than 30 or 40 of them.
It is perfectly prepared for raw devices, since a
tablespace in a raw device installation is simply an area
of blocks on a disk.
There are also disadvantages.
You can run out of space even if there are plenty GB's
free on your disks. You have to create tablespaces
explicitly.
If you've choosen inadequate extent size parameters, you
end up with high fragmented tables (slowing down) or get
stuck with running against maxextents, where only a reorg
(export/import) helps.
Jan
--
#======================================================================#
# It's easier to get forgiveness for being wrong than for being right. #
# Let's break this rule - forgive me. #
#================================================== JanWieck@Yahoo.com #
From tgl@sss.pgh.pa.us Fri Jun 16 11:00:40 2000
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To: Jan Wieck <JanWieck@Yahoo.com>
cc: Hiroshi Inoue <Inoue@tpf.co.jp>, Bruce Momjian <maillist@candle.pha.pa.us>,
PostgreSQL-development <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: Re: [HACKERS] Big 7.1 open items
In-reply-to: <200006161242.OAA15163@hot.jw.home>
References: <200006161242.OAA15163@hot.jw.home>
Comments: In-reply-to JanWieck@t-online.de (Jan Wieck)
message dated "Fri, 16 Jun 2000 14:42:12 +0200"
Date: Fri, 16 Jun 2000 11:00:35 -0400
Message-ID: <7181.961167635@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
Status: RO
JanWieck@t-online.de (Jan Wieck) writes:
> There are also disadvantages.
> You can run out of space even if there are plenty GB's
> free on your disks. You have to create tablespaces
> explicitly.
Not to mention the reverse: if I read this right, you have to suck
up your GB's long in advance of actually needing them. That's OK
for a machine that's dedicated to Oracle ... not so OK for smaller
installations, playpens, etc.
I'm not convinced that there's anything fundamentally wrong with
doing storage allocation in Unix files the way we have been.
(At least not when we're sitting atop a well-done filesystem,
which may leave the Linux folk out in the cold ;-).)
regards, tom lane
From tgl@sss.pgh.pa.us Fri Jun 16 12:01:03 2000
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To: Jan Wieck <JanWieck@Yahoo.com>
cc: Hiroshi Inoue <Inoue@tpf.co.jp>, Bruce Momjian <maillist@candle.pha.pa.us>,
PostgreSQL-development <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: Re: [HACKERS] Big 7.1 open items
In-reply-to: <200006161242.OAA15163@hot.jw.home>
References: <200006161242.OAA15163@hot.jw.home>
Comments: In-reply-to JanWieck@t-online.de (Jan Wieck)
message dated "Fri, 16 Jun 2000 14:42:12 +0200"
Date: Fri, 16 Jun 2000 11:46:41 -0400
Message-ID: <7458.961170401@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
Status: RO
JanWieck@t-online.de (Jan Wieck) writes:
> Tom Lane wrote:
>> It gets a little trickier if you want to be able to split
>> multi-gig tables across several tablespaces, though, since
>> you couldn't just append ".N" to the base table path in that
>> scenario.
>>
>> I'd be interested to know what sort of facilities Oracle
>> provides for managing huge tables...
> Oracle tablespaces are a collection of 1...n preallocated
> files. Each table then is bound to a tablespace and
> allocates extents (chunks) from those files.
OK, to get back to the point here: so in Oracle, tables can't cross
tablespace boundaries, but a tablespace itself could span multiple
disks?
Not sure if I like that better or worse than equating a tablespace
with a directory (so, presumably, all the files within it live on
one filesystem) and then trying to make tables able to span
tablespaces. We will need to do one or the other though, if we want
to have any significant improvement over the current state of affairs
for large tables.
One way is to play the flip-the-path-ordering game some more,
and access multiple-segment tables with pathnames like this:
.../TABLESPACE/RELATION -- first or only segment
.../TABLESPACE/N/RELATION -- N'th extension segment
This isn't any harder for md.c to deal with than what we do now,
but by making the /N subdirectories be symlinks, the dbadmin could
easily arrange for extension segments to go on different filesystems.
Also, since /N subdirectory symlinks can be added as needed,
expanding available space by attaching more disks isn't hard.
(If the admin hasn't pre-made a /N symlink when it's needed,
I'd envision the backend just automatically creating a plain
subdirectory so that it can extend the table.)
A limitation is that the N'th extension segments of all the relations
in a given tablespace have to be in the same place, but I don't see
that as a major objection. Worst case is you make a separate tablespace
for each of your multi-gig relations ... you're probably not going to
have a very large number of such relations, so this doesn't seem like
unmanageable admin complexity.
We'd still want to create some tools to help the dbadmin with slinging
all these symlinks around, of course. But I think it's critical to keep
the low-level file access protocol simple and reliable, which really
means minimizing the amount of information the backend needs to know to
figure out which file to write a page in. With something like the above
you only need to know the tablespace name (or more likely OID), the
relation OID (+name or not, depending on outcome of other argument),
and the offset in the table. No worse than now from the software's
point of view.
Comments?
regards, tom lane
From lockhart@alumni.caltech.edu Fri Jun 16 12:31:50 2000
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Date: Fri, 16 Jun 2000 16:27:22 +0000
From: Thomas Lockhart <lockhart@alumni.caltech.edu>
Organization: Yes
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To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Jan Wieck <JanWieck@Yahoo.com>, Hiroshi Inoue <Inoue@tpf.co.jp>,
Bruce Momjian <maillist@candle.pha.pa.us>,
PostgreSQL-development <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: Re: [HACKERS] Big 7.1 open items
References: <200006161242.OAA15163@hot.jw.home> <7458.961170401@sss.pgh.pa.us>
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Status: RO
> ... But I think it's critical to keep
> the low-level file access protocol simple and reliable, which really
> means minimizing the amount of information the backend needs to know
> to figure out which file to write a page in. With something like the
> above you only need to know the tablespace name (or more likely OID),
> the relation OID (+name or not, depending on outcome of other
> argument), and the offset in the table. No worse than now from the
> software's point of view.
> Comments?
I'm probably missing the context a bit, but imho we should try hard to
stay away from symlinks as the general solution for anything.
Sorry for being behind here, but to make sure I'm on the right page:
o tablespaces decouple storage from logical tables
o a database lives in a default tablespace, unless specified
o by default, a table will live in the default tablespace
o (eventually) a table can be split across tablespaces
Some thoughts:
o the ability to split single tables across disks was essential for
scalability when disks were small. But with RAID, NAS, etc etc isn't
that a smaller issue now?
o "tablespaces" would implement our less-developed "with location"
feature, right? Splitting databases, whole indices and whole tables
across storage is the biggest win for this work since more users will
use the feature.
o location information needs to travel with individual tables anyway.
From scrappy@hub.org Fri Jun 16 13:01:02 2000
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Date: Fri, 16 Jun 2000 13:50:37 -0300 (ADT)
From: The Hermit Hacker <scrappy@hub.org>
To: Bruce Momjian <pgman@candle.pha.pa.us>
cc: Tom Lane <tgl@sss.pgh.pa.us>, Hiroshi Inoue <Inoue@tpf.co.jp>,
Bruce Momjian <maillist@candle.pha.pa.us>,
PostgreSQL-development <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: Re: [HACKERS] Big 7.1 open items
In-Reply-To: <200006160224.WAA04345@candle.pha.pa.us>
Message-ID: <Pine.BSF.4.21.0006161349140.722-100000@thelab.hub.org>
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Status: RO
On Thu, 15 Jun 2000, Bruce Momjian wrote:
> > "Hiroshi Inoue" <Inoue@tpf.co.jp> writes:
> > > Now I like neither relname nor oid because it's not sufficient
> > > for my purpose.
> >
> > We should probably not do much of anything with this issue until
> > we have a clearer understanding of what we want to do about
> > tablespaces and schemas.
>
> Here is an analysis of our options:
>
> Work required Disadvantages
> ----------------------------------------------------------------------------
>
> Keep current system no work rename/create no rollback
>
> relname/oid but less work new pg_class column,
> no rename change filename not accurate on
> rename
>
> relname/oid with more work complex code
> rename change during
> vacuum
>
> oid filename less work, but confusing to admins
> need admin tools
My vote is with Tom on this one ... oid only ... the admin should be able
to do a quick SELECT on a table to find out the OID->table mapping, and I
believe its already been pointed out that you cant' just restore one file
anyway, so it kinda negates the "server isn't running problem" ...
From tgl@sss.pgh.pa.us Fri Jun 16 13:01:01 2000
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To: Thomas Lockhart <lockhart@alumni.caltech.edu>
cc: Jan Wieck <JanWieck@yahoo.com>, Hiroshi Inoue <Inoue@tpf.co.jp>,
Bruce Momjian <maillist@candle.pha.pa.us>,
PostgreSQL-development <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: Re: [HACKERS] Big 7.1 open items
In-reply-to: <394A556A.4EAC8B9A@alumni.caltech.edu>
References: <200006161242.OAA15163@hot.jw.home> <7458.961170401@sss.pgh.pa.us> <394A556A.4EAC8B9A@alumni.caltech.edu>
Comments: In-reply-to Thomas Lockhart <lockhart@alumni.caltech.edu>
message dated "Fri, 16 Jun 2000 16:27:22 -0000"
Date: Fri, 16 Jun 2000 12:54:00 -0400
Message-ID: <7747.961174440@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
Status: RO
Thomas Lockhart <lockhart@alumni.caltech.edu> writes:
>> ... But I think it's critical to keep
>> the low-level file access protocol simple and reliable, which really
>> means minimizing the amount of information the backend needs to know
>> to figure out which file to write a page in. With something like the
>> above you only need to know the tablespace name (or more likely OID),
>> the relation OID (+name or not, depending on outcome of other
>> argument), and the offset in the table. No worse than now from the
>> software's point of view.
>> Comments?
> I'm probably missing the context a bit, but imho we should try hard to
> stay away from symlinks as the general solution for anything.
Why?
regards, tom lane
From dhogaza@pacifier.com Fri Jun 16 14:55:00 2000
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Date: Fri, 16 Jun 2000 10:50:23 -0700
To: Tom Lane <tgl@sss.pgh.pa.us>, Jan Wieck <JanWieck@yahoo.com>
From: Don Baccus <dhogaza@pacifier.com>
Subject: Re: [HACKERS] Big 7.1 open items
Cc: Hiroshi Inoue <Inoue@tpf.co.jp>, Bruce Momjian <maillist@candle.pha.pa.us>,
PostgreSQL-development <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
In-Reply-To: <7458.961170401@sss.pgh.pa.us>
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<200006161242.OAA15163@hot.jw.home>
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Status: RO
At 11:46 AM 6/16/00 -0400, Tom Lane wrote:
>OK, to get back to the point here: so in Oracle, tables can't cross
>tablespace boundaries,
Right, the construct AFAIK is "create table/index foo on tablespace ..."
> but a tablespace itself could span multiple
>disks?
Right.
>Not sure if I like that better or worse than equating a tablespace
>with a directory (so, presumably, all the files within it live on
>one filesystem) and then trying to make tables able to span
>tablespaces. We will need to do one or the other though, if we want
>to have any significant improvement over the current state of affairs
>for large tables.
Oracle's way does a reasonable job of isolating the datamodel
from the details of the physical layout.
Take the OpenACS web toolkit, for instance. We could take
each module's tables and indices and assign them appropriately
to various dataspaces, then provide a separate .sql files with
only "create tablespace" statements in there.
By modifying that one central file, the toolkit installation
could be customized to run anything from a small site (one
disk with everything on it, ala my own personal webserver at
birdnotes.net) or a very large site with many spindles, with
various index and table structures spread out widely hither
and thither.
Given that the OpenACS datamodel is nearly 10K lines long (including
many comments, of course), being able to customize an installation
to such a degree by modifying a single file filled with "create
tablespaces" would be very attractive.
>One way is to play the flip-the-path-ordering game some more,
>and access multiple-segment tables with pathnames like this:
>
> .../TABLESPACE/RELATION -- first or only segment
> .../TABLESPACE/N/RELATION -- N'th extension segment
>
>This isn't any harder for md.c to deal with than what we do now,
>but by making the /N subdirectories be symlinks, the dbadmin could
>easily arrange for extension segments to go on different filesystems.
I personally dislike depending on symlinks to move stuff around.
Among other things, a pg_dump/restore (and presumably future
backup tools?) can't recreate the disk layout automatically.
>We'd still want to create some tools to help the dbadmin with slinging
>all these symlinks around, of course.
OK, if symlinks are simply an implementation detail hidden from the
dbadmin, and if the physical structure is kept in the db so it can
be rebuilt if necessary automatically, then I don't mind symlinks.
> But I think it's critical to keep
>the low-level file access protocol simple and reliable, which really
>means minimizing the amount of information the backend needs to know to
>figure out which file to write a page in. With something like the above
>you only need to know the tablespace name (or more likely OID), the
>relation OID (+name or not, depending on outcome of other argument),
>and the offset in the table. No worse than now from the software's
>point of view.
Make the code that creates and otherwise manipulates tablespaces
do the work, while keeping the low-level file access protocol simple.
Yes, this approach sounds very good to me.
- Don Baccus, Portland OR <dhogaza@pacifier.com>
Nature photos, on-line guides, Pacific Northwest
Rare Bird Alert Service and other goodies at
http://donb.photo.net.
From pgsql-hackers-owner+M3500@hub.org Fri Jun 16 14:55:10 2000
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Date: Fri, 16 Jun 2000 11:14:35 -0700
To: Thomas Lockhart <lockhart@alumni.caltech.edu>,
Tom Lane <tgl@sss.pgh.pa.us>
From: Don Baccus <dhogaza@pacifier.com>
Subject: Re: [HACKERS] Big 7.1 open items
Cc: Jan Wieck <JanWieck@yahoo.com>, Hiroshi Inoue <Inoue@tpf.co.jp>,
Bruce Momjian <maillist@candle.pha.pa.us>,
PostgreSQL-development <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
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Status: RO
At 04:27 PM 6/16/00 +0000, Thomas Lockhart wrote:
>Sorry for being behind here, but to make sure I'm on the right page:
>o tablespaces decouple storage from logical tables
>o a database lives in a default tablespace, unless specified
>o by default, a table will live in the default tablespace
>o (eventually) a table can be split across tablespaces
Or tablespaces across filesystems/mountpoints whatever.
>Some thoughts:
>o the ability to split single tables across disks was essential for
>scalability when disks were small. But with RAID, NAS, etc etc isn't
>that a smaller issue now?
Yes for size issues, I should think, especially if you have the
money for a large RAID subsystem. But for throughput performance,
control over which spindles particularly busy tables and indices
go on would still seem to be pretty relevant, when they're being
updated a lot. In order to minimize seek times.
I really can't say how important this is in reality. Oracle-world
folks still talk about this kind of optimization being important,
but I'm not personally running any kind of database-backed website
that's busy enough or contains enough storage to worry about it.
>o "tablespaces" would implement our less-developed "with location"
>feature, right? Splitting databases, whole indices and whole tables
>across storage is the biggest win for this work since more users will
>use the feature.
>o location information needs to travel with individual tables anyway.
- Don Baccus, Portland OR <dhogaza@pacifier.com>
Nature photos, on-line guides, Pacific Northwest
Rare Bird Alert Service and other goodies at
http://donb.photo.net.
From tgl@sss.pgh.pa.us Fri Jun 16 15:00:55 2000
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To: Don Baccus <dhogaza@pacifier.com>
cc: Jan Wieck <JanWieck@yahoo.com>, Hiroshi Inoue <Inoue@tpf.co.jp>,
Bruce Momjian <maillist@candle.pha.pa.us>,
PostgreSQL-development <pgsql-hackers@postgresql.org>,
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Subject: Re: [HACKERS] Big 7.1 open items
In-reply-to: <3.0.1.32.20000616105023.011dbdb0@mail.pacifier.com>
References: <200006161242.OAA15163@hot.jw.home> <200006161242.OAA15163@hot.jw.home> <3.0.1.32.20000616105023.011dbdb0@mail.pacifier.com>
Comments: In-reply-to Don Baccus <dhogaza@pacifier.com>
message dated "Fri, 16 Jun 2000 10:50:23 -0700"
Date: Fri, 16 Jun 2000 15:00:10 -0400
Message-ID: <8244.961182010@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
Status: RO
Don Baccus <dhogaza@pacifier.com> writes:
>> This isn't any harder for md.c to deal with than what we do now,
>> but by making the /N subdirectories be symlinks, the dbadmin could
>> easily arrange for extension segments to go on different filesystems.
> I personally dislike depending on symlinks to move stuff around.
> Among other things, a pg_dump/restore (and presumably future
> backup tools?) can't recreate the disk layout automatically.
Good point, we'd need some way of saving/restoring the tablespace
structures.
>> We'd still want to create some tools to help the dbadmin with slinging
>> all these symlinks around, of course.
> OK, if symlinks are simply an implementation detail hidden from the
> dbadmin, and if the physical structure is kept in the db so it can
> be rebuilt if necessary automatically, then I don't mind symlinks.
I'm not sure about keeping it in the db --- creates a bit of a
chicken-and-egg problem doesn't it? Maybe there needs to be a
"system database" that has nailed-down pathnames (no tablespaces
for you baby) and contains the critical installation-wide tables
like pg_database, pg_user, pg_tablespace. A restore would have
to restore these tables first anyway.
> Make the code that creates and otherwise manipulates tablespaces
> do the work, while keeping the low-level file access protocol simple.
Right, that's the bottom line for me.
regards, tom lane
From reedstrm@rice.edu Fri Jun 16 16:51:50 2000
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Date: Fri, 16 Jun 2000 14:35:28 -0500
From: "Ross J. Reedstrom" <reedstrm@rice.edu>
To: Thomas Lockhart <lockhart@alumni.caltech.edu>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Jan Wieck <JanWieck@yahoo.com>,
Hiroshi Inoue <Inoue@tpf.co.jp>,
Bruce Momjian <maillist@candle.pha.pa.us>,
PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: [HACKERS] Big 7.1 open items
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In-Reply-To: <394A556A.4EAC8B9A@alumni.caltech.edu>; from lockhart@alumni.caltech.edu on Fri, Jun 16, 2000 at 04:27:22PM +0000
Status: RO
On Fri, Jun 16, 2000 at 04:27:22PM +0000, Thomas Lockhart wrote:
> > ... But I think it's critical to keep
> > the low-level file access protocol simple and reliable, which really
> > means minimizing the amount of information the backend needs to know
> > to figure out which file to write a page in. With something like the
> > above you only need to know the tablespace name (or more likely OID),
> > the relation OID (+name or not, depending on outcome of other
> > argument), and the offset in the table. No worse than now from the
> > software's point of view.
> > Comments?
I think the backend needs a per table token that indicates how
to get at the physical bits of the file. Whether that's a filename
alone, filename with path, oid, key to a smgr hash table or something
else, it's opaque above the smgr routines.
Hmm, now I'm thinking, since the tablespace discussion has been reopened,
the way to go about coding all this is to reactivate the smgr code: how
about I leave the existing md smgr as is, and clone it, call it md2 or
something, and start messing with adding features there?
>
> I'm probably missing the context a bit, but imho we should try hard to
> stay away from symlinks as the general solution for anything.
>
> Sorry for being behind here, but to make sure I'm on the right page:
> o tablespaces decouple storage from logical tables
> o a database lives in a default tablespace, unless specified
> o by default, a table will live in the default tablespace
> o (eventually) a table can be split across tablespaces
>
> Some thoughts:
> o the ability to split single tables across disks was essential for
> scalability when disks were small. But with RAID, NAS, etc etc isn't
> that a smaller issue now?
> o "tablespaces" would implement our less-developed "with location"
> feature, right? Splitting databases, whole indices and whole tables
> across storage is the biggest win for this work since more users will
> use the feature.
> o location information needs to travel with individual tables anyway.
I was juist thinking that that discussion needed some summation.
Some links to historic discussion:
This one is Vadim saying WAL will need oids names:
http://www.postgresql.org/mhonarc/pgsql-hackers/1999-11/msg00809.html
A longer discussion kicked off by Don Baccus:
http://www.postgresql.org/mhonarc/pgsql-hackers/2000-01/msg00510.html
Tom suggesting OIDs to allow rollback:
http://www.postgresql.org/mhonarc/pgsql-hackers/2000-03/msg00119.html
Martin Neumann posted an question on dataspaces:
(can't find it in the offical archives: looks like March 2000, 10-29 is
missing. here's my copy: don't beat on it! n particular, since I threw
it together for local access, it's one _big_ index page)
http://cooker.ir.rice.edu/postgresql/msg20257.html
(in that thread is a post where I mention blindwrites and getting rid
of GetRawDatabaseInfo)
Martin later posted an RFD on tablespaces:
http://cooker.ir.rice.edu/postgresql/msg20490.html
Here's Hor<6F>k Daniel with a patch for discussion, implementing dataspaces
on a per database level:
http://cooker.ir.rice.edu/postgresql/msg20498.html
Ross
--
Ross J. Reedstrom, Ph.D., <reedstrm@rice.edu>
NSBRI Research Scientist/Programmer
Computer and Information Technology Institute
Rice University, 6100 S. Main St., Houston, TX 77005
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Date: Fri, 16 Jun 2000 12:37:36 -0700
To: Tom Lane <tgl@sss.pgh.pa.us>
From: Don Baccus <dhogaza@pacifier.com>
Subject: Re: [HACKERS] Big 7.1 open items
Cc: Jan Wieck <JanWieck@yahoo.com>, Hiroshi Inoue <Inoue@tpf.co.jp>,
Bruce Momjian <maillist@candle.pha.pa.us>,
PostgreSQL-development <pgsql-hackers@postgresql.org>,
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Status: RO
At 03:00 PM 6/16/00 -0400, Tom Lane wrote:
>> OK, if symlinks are simply an implementation detail hidden from the
>> dbadmin, and if the physical structure is kept in the db so it can
>> be rebuilt if necessary automatically, then I don't mind symlinks.
>
>I'm not sure about keeping it in the db --- creates a bit of a
>chicken-and-egg problem doesn't it?
Not if the tablespace creates preceeds the tables stored in them.
> Maybe there needs to be a
>"system database" that has nailed-down pathnames (no tablespaces
>for you baby) and contains the critical installation-wide tables
>like pg_database, pg_user, pg_tablespace. A restore would have
>to restore these tables first anyway.
Oh, I see. Yes, when I've looked into this and have thought about
it I've assumed that there would always be a known starting point
which would contain the installation-wide tables.
>From a practical point of view, I don't think that's really a
problem.
I've not looked into how Oracle does this, I assume it builds
a system tablespace on one of the initial mount points you give
it when you install the thing. The paths to the mount points
are stored in specific files known to Oracle, I think. It's
been over a year (not long enough!) since I've set up Oracle...
- Don Baccus, Portland OR <dhogaza@pacifier.com>
Nature photos, on-line guides, Pacific Northwest
Rare Bird Alert Service and other goodies at
http://donb.photo.net.
From pgsql-hackers-owner+M3512@hub.org Fri Jun 16 17:31:04 2000
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From: "Ross J. Reedstrom" <reedstrm@rice.edu>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-hackers@postgresql.org
Subject: Re: [HACKERS] Big 7.1 open items
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On Thu, Jun 15, 2000 at 07:53:52PM -0400, Tom Lane wrote:
> "Ross J. Reedstrom" <reedstrm@rice.edu> writes:
> > On Thu, Jun 15, 2000 at 03:11:52AM -0400, Tom Lane wrote:
> >> "Ross J. Reedstrom" <reedstrm@rice.edu> writes:
> >>>> Any strong objections to the mixed relname_oid solution?
> >>
> >> Yes!
>
> > The plan here was to let VACUUM handle renaming the file, since it
> > will already have all the necessary locks. This shortens the window
> > of confusion. ALTER TABLE RENAME doesn't happen that often, really -
> > the relname is there just for human consumption, then.
>
> Yeah, I've seen tons of discussion of how if we do this, that, and
> the other thing, and be prepared to fix up some other things in case
> of crash recovery, we can make it work with filename == relname + OID
> (where relname tracks logical name, at least at some remove).
>
> Probably. Assuming nobody forgets anything.
I agree, it seems a major undertaking, at first glance. And second. Even
third. Especially for someone who hasn't 'earned his spurs' yet. as
it were.
> I'm just trying to point out that that's a huge amount of pretty
> delicate mechanism. The amount of work required to make it trustworthy
> looks to me to dwarf the admin tools that Bruce is complaining about.
> And we only have a few people competent to do the work. (With all
> due respect, Ross, if you weren't already aware of the implications
> for mdblindwrt, I have to wonder what else you missed.)
Ah, you knew that comment would come back to haunt me (I have a
tendency to think out loud, even if checking and coming back latter
would be better;-) In fact, there's no problem, and never was, since the
buffer->blind.relname is filled in via RelationGetPhysicalRelationName,
just like every other path that requires direct file access. I just
didn't remember that I had in fact checked it (it's been a couple months,
and I just got back from vacation ;-)
Actually, Once I re-checked it, the code looked very familiar. I had
spent time looking at the blind write code in the context of getting
rid of the only non-startup use of GetRawDatabaseInfo.
As to missing things: I'm leaning heavily on Bruce's previous
work for temp tables, to seperate the two uses of relname, via the
RelationGetRelationName and RelationGetPhysicalRelationName. There are
102 uses of the first in the current code (many in elog messages), and
only 11 of the second. If I'd had to do the original work of finding
every use of relname, and catagorizing it, I agree I'm not (yet) up to
it, but I have more confidence in Bruce's (already tested) work.
>
> Filename == OID is so simple, reliable, and straightforward by
> comparison that I think the decision is a no-brainer.
>
Perhaps. Changing the label of the file on disk still requires finding
all the code that assumes it knows what that name is, and changing it.
Same work.
> If we could afford to sink unlimited time into this one issue then
> it might make sense to do it the hard way, but we have enough
> important stuff on our TODO list to keep us all busy for years ---
> I cannot believe that it's an effective use of our time to do this.
>
The joys of Open Development. You've spent a fair amount of time trying
to convince _me_ not to waste my time. Thanks, but I'm pretty bull headed
sometimes. Since I've already done something of the work, take a look
at what I've got, and then tell me I'm wasting my time, o.k.?
>
> > Hmm, what's all this with functions in catalog.c that are only called by
> > smgr/md.c? seems to me that anything having to do with physical storage
> > (like the path!) belongs in the smgr abstraction.
>
> Yeah, there's a bunch of stuff that should have been implemented by
> adding new smgr entry points, but wasn't. It should be pushed down.
> (I can't resist pointing out that one of those things is physical
> relation rename, which will go away and not *need* to be pushed down
> if we do it the way I want.)
>
Oh, I agree completely. In fact, As I said to Hiroshi last time this came
up, I think of the field in pg_class an an opaque token, to be filled in
by the smgr, and only used by code further up to hand back to the smgr
routines. Same should be true of the buffer->blind struct.
Ross
--
Ross J. Reedstrom, Ph.D., <reedstrm@rice.edu>
NSBRI Research Scientist/Programmer
Computer and Information Technology Institute
Rice University, 6100 S. Main St., Houston, TX 77005
From Inoue@tpf.co.jp Fri Jun 16 19:31:00 2000
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From: "Hiroshi Inoue" <Inoue@tpf.co.jp>
To: "Tom Lane" <tgl@sss.pgh.pa.us>, "Jan Wieck" <JanWieck@Yahoo.com>
Cc: "Bruce Momjian" <maillist@candle.pha.pa.us>,
"PostgreSQL-development" <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: RE: [HACKERS] Big 7.1 open items
Date: Sat, 17 Jun 2000 08:11:08 +0900
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> -----Original Message-----
> From: Tom Lane [mailto:tgl@sss.pgh.pa.us]
>
> JanWieck@t-online.de (Jan Wieck) writes:
> > There are also disadvantages.
>
> > You can run out of space even if there are plenty GB's
> > free on your disks. You have to create tablespaces
> > explicitly.
>
> Not to mention the reverse: if I read this right, you have to suck
> up your GB's long in advance of actually needing them. That's OK
> for a machine that's dedicated to Oracle ... not so OK for smaller
> installations, playpens, etc.
>
I've had an anxiety about the way like Oracle's preallocation.
It had not been easy for me to estimate the extent size in
Oracle. Maybe it would lose the simplicity of environment
settings which is one of the biggest advantage of PostgreSQL.
It seems that we should also provide not_preallocated DATAFILE
when many_tables_in_a_file storage manager is introduced.
Regards.
Hiroshi Inoue
Inoue@tpf.co.jp
From tgl@sss.pgh.pa.us Fri Jun 16 19:31:01 2000
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To: "Ross J. Reedstrom" <reedstrm@rice.edu>
cc: Thomas Lockhart <lockhart@alumni.caltech.edu>,
Jan Wieck <JanWieck@Yahoo.com>, Hiroshi Inoue <Inoue@tpf.co.jp>,
Bruce Momjian <maillist@candle.pha.pa.us>,
PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: [HACKERS] Big 7.1 open items
In-reply-to: <20000616143528.A28920@rice.edu>
References: <200006161242.OAA15163@hot.jw.home> <7458.961170401@sss.pgh.pa.us> <394A556A.4EAC8B9A@alumni.caltech.edu> <20000616143528.A28920@rice.edu>
Comments: In-reply-to "Ross J. Reedstrom" <reedstrm@rice.edu>
message dated "Fri, 16 Jun 2000 14:35:28 -0500"
Date: Fri, 16 Jun 2000 19:16:37 -0400
Message-ID: <9271.961197397@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
Status: RO
"Ross J. Reedstrom" <reedstrm@rice.edu> writes:
> I think the backend needs a per table token that indicates how
> to get at the physical bits of the file. Whether that's a filename
> alone, filename with path, oid, key to a smgr hash table or something
> else, it's opaque above the smgr routines.
Except to the commands that provide the user interface for tablespaces
and so forth. And there aren't all that many places that deal with
physical filenames anyway. It would be a good idea to try to be a
little stricter about this, but I'm not sure you can make the separation
a whole lot cleaner than it is now ... with the exception of the obvious
bogosities like "rename table" being done above the smgr level. (But,
as I said, I want to see that code go away, not just get moved into
smgr...)
> Hmm, now I'm thinking, since the tablespace discussion has been reopened,
> the way to go about coding all this is to reactivate the smgr code: how
> about I leave the existing md smgr as is, and clone it, call it md2 or
> something, and start messing with adding features there?
Um, well, you can't have it both ways. If you're going to change/fix
the assumptions of code above the smgr, then you've got to update md
at the same time to match your new definition of the smgr interface.
Won't do much good to have a playpen smgr if the "standard" one is
broken.
One thing I have been thinking would be a good idea is to take the
relcache out of the bufmgr/smgr interfaces. The relcache is a
higher-level concept and ought not be known to bufmgr or smgr; they
ought to work with some low-level data structure or token for relations.
We might be able to eliminate the whole concept of "blind write" if we
do that. There are other problems with the relcache dependency: entries
in relcache can get blown away at inopportune times due to shared cache
inval, and it doesn't provide a good home for tokens for multiple
"versions" of a relation if we go with the fill-a-new-physical-file
approach to CLUSTER and so on.
Hmm, if you replace relcache in the smgr interfaces with pointers to
an smgr-maintained data structure, that might be the same thing that
you are alluding to above about an smgr hash table.
One thing *not* to do is add yet a third layer of data structure on
top of the ones already maintained in fd.c and md.c. Whatever extra
data might be needed here should be added to md.c's tables, I think,
and then the tokens used in the smgr interface would be pointers into
that table.
regards, tom lane
From tgl@sss.pgh.pa.us Fri Jun 16 19:30:43 2000
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To: "Hiroshi Inoue" <Inoue@tpf.co.jp>
cc: "Jan Wieck" <JanWieck@Yahoo.com>,
"Bruce Momjian" <maillist@candle.pha.pa.us>,
"PostgreSQL-development" <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: Re: [HACKERS] Big 7.1 open items
In-reply-to: <EKEJJICOHDIEMGPNIFIJAEADCCAA.Inoue@tpf.co.jp>
References: <EKEJJICOHDIEMGPNIFIJAEADCCAA.Inoue@tpf.co.jp>
Comments: In-reply-to "Hiroshi Inoue" <Inoue@tpf.co.jp>
message dated "Sat, 17 Jun 2000 08:11:08 +0900"
Date: Fri, 16 Jun 2000 19:30:25 -0400
Message-ID: <9317.961198225@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
Status: ROr
"Hiroshi Inoue" <Inoue@tpf.co.jp> writes:
> It seems that we should also provide not_preallocated DATAFILE
> when many_tables_in_a_file storage manager is introduced.
Several people in this thread have been talking like a
single-physical-file storage manager is in our future, but I can't
recall anyone saying that they were going to do such a thing or even
presenting reasons why it'd be a good idea.
Seems to me that physical file per relation is considerably better for
our purposes. It's easier to figure out what's going on for admin and
debug work, it means less lock contention among different backends
appending concurrently to different relations, and it gives the OS a
better shot at doing effective read-ahead on sequential scans.
So why all the enthusiasm for multi-tables-per-file?
regards, tom lane
From chris@bitmead.com Fri Jun 16 21:01:02 2000
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From: Chris Bitmead <chris@bitmead.com>
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To: Bruce Momjian <pgman@candle.pha.pa.us>
CC: Tom Lane <tgl@sss.pgh.pa.us>, Hiroshi Inoue <Inoue@tpf.co.jp>,
Jan Wieck <JanWieck@Yahoo.com>,
Bruce Momjian <maillist@candle.pha.pa.us>,
PostgreSQL-development <pgsql-hackers@postgreSQL.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: Re: [HACKERS] Big 7.1 open items
References: <200006170008.UAA06798@candle.pha.pa.us>
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Status: RO
> > So why all the enthusiasm for multi-tables-per-file?
It allows you to use raw partitions which stop the OS double buffering
and wasting half of memory, as well as removing the overhead of indirect
blocks in the file system.
From Inoue@tpf.co.jp Sat Jun 17 06:00:59 2000
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From: "Hiroshi Inoue" <Inoue@tpf.co.jp>
To: "Bruce Momjian" <pgman@candle.pha.pa.us>, "Tom Lane" <tgl@sss.pgh.pa.us>
Cc: "Jan Wieck" <JanWieck@Yahoo.com>,
"Bruce Momjian" <maillist@candle.pha.pa.us>,
"PostgreSQL-development" <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: RE: [HACKERS] Big 7.1 open items
Date: Sat, 17 Jun 2000 18:38:29 +0900
Message-ID: <EKEJJICOHDIEMGPNIFIJEEAKCCAA.Inoue@tpf.co.jp>
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Status: RO
> -----Original Message-----
> From: Bruce Momjian [mailto:pgman@candle.pha.pa.us]
> >
> > So why all the enthusiasm for multi-tables-per-file?
>
> No idea. I thought Vadim mentioned it, but I am not sure anymore. I
> certainly like our current system.
>
Oops,I'm not so enthusiastic for multi_tables_per_file smgr.
I believe that Ross and I have taken a practical way that doesn't
break current file_per_table smgr.
However it seems very natural to take multi_tables_per_file
smgr into account when we consider TABLESPACE concept.
Because TABLESPACE is an encapsulation,it should have
a possibility to handle multi_tables_per_file smgr IMHO.
Regards.
Hiroshi Inoue
Inoue@tpf.co.jp
From tgl@sss.pgh.pa.us Sat Jun 17 12:31:08 2000
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To: "Hiroshi Inoue" <Inoue@tpf.co.jp>
cc: "Bruce Momjian" <pgman@candle.pha.pa.us>, "Jan Wieck" <JanWieck@Yahoo.com>,
"Bruce Momjian" <maillist@candle.pha.pa.us>,
"PostgreSQL-development" <pgsql-hackers@postgreSQL.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: Re: [HACKERS] Big 7.1 open items
In-reply-to: <EKEJJICOHDIEMGPNIFIJEEAKCCAA.Inoue@tpf.co.jp>
References: <EKEJJICOHDIEMGPNIFIJEEAKCCAA.Inoue@tpf.co.jp>
Comments: In-reply-to "Hiroshi Inoue" <Inoue@tpf.co.jp>
message dated "Sat, 17 Jun 2000 18:38:29 +0900"
Date: Sat, 17 Jun 2000 12:11:18 -0400
Message-ID: <18821.961258278@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
Status: RO
"Hiroshi Inoue" <Inoue@tpf.co.jp> writes:
> However it seems very natural to take multi_tables_per_file
> smgr into account when we consider TABLESPACE concept.
> Because TABLESPACE is an encapsulation,it should have
> a possibility to handle multi_tables_per_file smgr IMHO.
OK, I see: you're just saying that the tablespace stuff should be
designed in such a way that it would work with a non-file-per-table
smgr. Agreed, that'd be a good check of a clean design, and someday
we might need it...
regards, tom lane
From tgl@sss.pgh.pa.us Sun Jun 18 12:30:59 2000
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To: Bruce Momjian <pgman@candle.pha.pa.us>
cc: Jan Wieck <JanWieck@Yahoo.com>, Hiroshi Inoue <Inoue@tpf.co.jp>,
PostgreSQL-development <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: Re: [HACKERS] Big 7.1 open items
In-reply-to: <200006181333.JAA01648@candle.pha.pa.us>
References: <200006181333.JAA01648@candle.pha.pa.us>
Comments: In-reply-to Bruce Momjian <pgman@candle.pha.pa.us>
message dated "Sun, 18 Jun 2000 09:33:44 -0400"
Date: Sun, 18 Jun 2000 12:06:29 -0400
Message-ID: <12160.961344389@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
Status: ROr
Bruce Momjian <pgman@candle.pha.pa.us> writes:
> ... We could even get fancy and
> round-robin through all the extents directories, looping around to the
> beginning when we run out of them. That sounds nice.
That sounds horrible. There's no way to tell which extent directory
extent N goes into except by scanning the location directory to find
out how many extent subdirectories there are (so that you can compute
N modulo number-of-directories). Do you want to pay that price on every
file open?
Worse, what happens when you add another extent directory? You can't
find your old extents anymore, that's what, because they're not in the
right place (N modulo number-of-directories just changed). Since the
extents are presumably on different volumes, you're talking about
physical file moves to get them where they should be. You probably
can't add a new extent without shutting down the entire database while
you reshuffle files --- at the very least you'd need to get exclusive
locks on all the tables in that tablespace.
Also, you'll get filename conflicts from multiple extents of a single
table appearing in one of the recycled extent dirs. You could work
around it by using the non-modulo'd N as part of the final file name,
but that just adds more complexity and makes the filename-generation
machinery that much more closely tied to this specific way of doing
things.
The right way to do this is that extent N goes into extents subdirectory
N, period. If there's no such subdirectory, create one on-the-fly as a
plain subdirectory of the location directory. The dbadmin can easily
create secondary extent symlinks *in advance of their being needed*.
Reorganizing later is much more painful since it requires moving
physical files, but I think that'd be true no matter what. At least
we should see to it that adding more space in advance of needing it is
painless.
It's possible to do it that way (auto-create extent subdir if needed)
without tying the md.c machinery real closely to a specific filename
creation procedure: it's just the same sort of thing as install programs
customarily do. "If you fail to create a file, try creating its
ancestor directory." We'd have to think about whether it'd be a good
idea to allow auto-creation of more than one level of directory; offhand
it seems that needing to make more than one level is probably a sign of
an erroneous path, not need for another extent subdirectory.
regards, tom lane
From dhogaza@pacifier.com Sun Jun 18 20:01:00 2000
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Date: Sun, 18 Jun 2000 16:43:42 -0700
To: Bruce Momjian <pgman@candle.pha.pa.us>, Tom Lane <tgl@sss.pgh.pa.us>
From: Don Baccus <dhogaza@pacifier.com>
Subject: Re: [HACKERS] Big 7.1 open items
Cc: Jan Wieck <JanWieck@yahoo.com>, Hiroshi Inoue <Inoue@tpf.co.jp>,
PostgreSQL-development <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
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Status: ROr
At 06:50 PM 6/18/00 -0400, Bruce Momjian wrote:
>If we eliminate the round-robin idea, what did people think of the rest
>of the ideas?
Why invent new syntax when "create tablespace" is something a lot
of folks will recognize?
And why not use "create table ... using ... "? In other words,
Oracle-compatible for this construct? Sure, Postgres doesn't
have to follow Oraclisms but picking an existing contruct means
at least SOME folks can import a datamodel without having to
edit it.
Does your proposal break the smgr abstraction, i.e. does it
preclude later efforts to (say) implement an (optional)
raw-device storage manager?
- Don Baccus, Portland OR <dhogaza@pacifier.com>
Nature photos, on-line guides, Pacific Northwest
Rare Bird Alert Service and other goodies at
http://donb.photo.net.
From pgsql-hackers-owner+M3571@hub.org Sun Jun 18 23:28:13 2000
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From: Bruce Momjian <pgman@candle.pha.pa.us>
Message-Id: <200006190313.XAA23541@candle.pha.pa.us>
Subject: Re: [HACKERS] Big 7.1 open items
In-Reply-To: <12160.961344389@sss.pgh.pa.us> "from Tom Lane at Jun 18, 2000 12:06:29
pm"
To: Tom Lane <tgl@sss.pgh.pa.us>
Date: Sun, 18 Jun 2000 23:13:44 -0400 (EDT)
CC: Jan Wieck <JanWieck@Yahoo.com>, Hiroshi Inoue <Inoue@tpf.co.jp>,
PostgreSQL-development <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
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Status: RO
My basic proposal is that we optionally allow symlinks when creating
tablespace directories, and that we interrogate those symlinks during a
dump so administrators can move tablespaces around without having to
modify environment variables or system tables.
I also suggested creating an extent directory to hold extents, like
extent/2 and extent/3. This will allow administration for smaller sites
to be simpler.
--
Bruce Momjian | http://www.op.net/~candle
pgman@candle.pha.pa.us | (610) 853-3000
+ If your life is a hard drive, | 830 Blythe Avenue
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026
From dhogaza@pacifier.com Mon Jun 19 00:31:00 2000
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Date: Sun, 18 Jun 2000 21:07:48 -0700
To: Bruce Momjian <pgman@candle.pha.pa.us>, Tom Lane <tgl@sss.pgh.pa.us>
From: Don Baccus <dhogaza@pacifier.com>
Subject: Re: [HACKERS] Big 7.1 open items
Cc: Jan Wieck <JanWieck@yahoo.com>, Hiroshi Inoue <Inoue@tpf.co.jp>,
PostgreSQL-development <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
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Status: RO
At 11:13 PM 6/18/00 -0400, Bruce Momjian wrote:
>My basic proposal is that we optionally allow symlinks when creating
>tablespace directories, and that we interrogate those symlinks during a
>dump so administrators can move tablespaces around without having to
>modify environment variables or system tables.
If they can move them around from within the db, they'll have no need to
move them around from outside the db.
I don't quite understand your devotion to using filesystem commands
outside the database to do database administration.
- Don Baccus, Portland OR <dhogaza@pacifier.com>
Nature photos, on-line guides, Pacific Northwest
Rare Bird Alert Service and other goodies at
http://donb.photo.net.
From pgsql-hackers-owner+M3573@hub.org Mon Jun 19 01:31:02 2000
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To: Bruce Momjian <pgman@candle.pha.pa.us>
cc: Jan Wieck <JanWieck@yahoo.com>, Hiroshi Inoue <Inoue@tpf.co.jp>,
PostgreSQL-development <pgsql-hackers@postgreSQL.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: Re: [HACKERS] Big 7.1 open items
In-reply-to: <200006190313.XAA23541@candle.pha.pa.us>
References: <200006190313.XAA23541@candle.pha.pa.us>
Comments: In-reply-to Bruce Momjian <pgman@candle.pha.pa.us>
message dated "Sun, 18 Jun 2000 23:13:44 -0400"
Date: Mon, 19 Jun 2000 00:25:52 -0400
Message-ID: <9514.961388752@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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Bruce Momjian <pgman@candle.pha.pa.us> writes:
> I also suggested creating an extent directory to hold extents, like
> extent/2 and extent/3. This will allow administration for smaller sites
> to be simpler.
I don't see the value in creating an extra level of directory --- seems
that just adds one more Unix directory-lookup cycle to each file open,
without any apparent return. What's wrong with extent directory names
like extent2, extent3, etc?
Obviously the extent dirnames must be chosen so they can't conflict
with table filenames, but that's easily done. For example, if table
files are named like 'OID_xxx' then 'extentN' will never conflict.
regards, tom lane
From tgl@sss.pgh.pa.us Mon Jun 19 00:30:58 2000
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To: Don Baccus <dhogaza@pacifier.com>
cc: Bruce Momjian <pgman@candle.pha.pa.us>, Jan Wieck <JanWieck@yahoo.com>,
Hiroshi Inoue <Inoue@tpf.co.jp>,
PostgreSQL-development <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: Re: [HACKERS] Big 7.1 open items
In-reply-to: <3.0.1.32.20000618210748.011d1c40@mail.pacifier.com>
References: <12160.961344389@sss.pgh.pa.us> <3.0.1.32.20000618210748.011d1c40@mail.pacifier.com>
Comments: In-reply-to Don Baccus <dhogaza@pacifier.com>
message dated "Sun, 18 Jun 2000 21:07:48 -0700"
Date: Mon, 19 Jun 2000 00:28:14 -0400
Message-ID: <9532.961388894@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
Status: ROr
Don Baccus <dhogaza@pacifier.com> writes:
> If they can move them around from within the db, they'll have no need to
> move them around from outside the db.
> I don't quite understand your devotion to using filesystem commands
> outside the database to do database administration.
Being *able* to use filesystem commands to see/fix what's going on is a
good thing, particularly from a development/debugging standpoint. But
I agree we want to have within-the-system admin commands to do the same
things.
regards, tom lane
From pgsql-hackers-owner+M3574@hub.org Mon Jun 19 01:31:01 2000
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To: Don Baccus <dhogaza@pacifier.com>
cc: Bruce Momjian <pgman@candle.pha.pa.us>, Jan Wieck <JanWieck@yahoo.com>,
Hiroshi Inoue <Inoue@tpf.co.jp>,
PostgreSQL-development <pgsql-hackers@postgreSQL.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: Re: [HACKERS] Big 7.1 open items
In-reply-to: <3.0.1.32.20000618210748.011d1c40@mail.pacifier.com>
References: <12160.961344389@sss.pgh.pa.us> <3.0.1.32.20000618210748.011d1c40@mail.pacifier.com>
Comments: In-reply-to Don Baccus <dhogaza@pacifier.com>
message dated "Sun, 18 Jun 2000 21:07:48 -0700"
Date: Mon, 19 Jun 2000 00:28:14 -0400
Message-ID: <9532.961388894@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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Don Baccus <dhogaza@pacifier.com> writes:
> If they can move them around from within the db, they'll have no need to
> move them around from outside the db.
> I don't quite understand your devotion to using filesystem commands
> outside the database to do database administration.
Being *able* to use filesystem commands to see/fix what's going on is a
good thing, particularly from a development/debugging standpoint. But
I agree we want to have within-the-system admin commands to do the same
things.
regards, tom lane
From dhogaza@pacifier.com Mon Jun 19 00:58:39 2000
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Date: Sun, 18 Jun 2000 21:33:19 -0700
To: Tom Lane <tgl@sss.pgh.pa.us>
From: Don Baccus <dhogaza@pacifier.com>
Subject: Re: [HACKERS] Big 7.1 open items
Cc: Bruce Momjian <pgman@candle.pha.pa.us>, Jan Wieck <JanWieck@yahoo.com>,
Hiroshi Inoue <Inoue@tpf.co.jp>,
PostgreSQL-development <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
In-Reply-To: <9532.961388894@sss.pgh.pa.us>
References: <3.0.1.32.20000618210748.011d1c40@mail.pacifier.com>
<12160.961344389@sss.pgh.pa.us>
<3.0.1.32.20000618210748.011d1c40@mail.pacifier.com>
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At 12:28 AM 6/19/00 -0400, Tom Lane wrote:
>Being *able* to use filesystem commands to see/fix what's going on is a
>good thing, particularly from a development/debugging standpoint.
Of course it's a crutch for development, but outside of development
circles few users will know how to use the OS in regard to the
database.
Assuming PG takes off. Of course, if it remains the realm of the
dedicated hard-core hacker, I'm wrong.
I have nothing against preserving the ability to use filesystem
commands if there's no significant costs inherent with this approach.
I'd view the breaking of smgr abstraction as a significant cost (though
I agree with Ross that it Bruce's proposal shouldn't require that, I
asked my question to flush Bruce out, if you will, because he's
devoted to a particular outside-the-db management model).
> But
>I agree we want to have within-the-system admin commands to do the same
>things.
MUST have, I should think.
- Don Baccus, Portland OR <dhogaza@pacifier.com>
Nature photos, on-line guides, Pacific Northwest
Rare Bird Alert Service and other goodies at
http://donb.photo.net.
From Inoue@tpf.co.jp Mon Jun 19 12:31:17 2000
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From: "Hiroshi Inoue" <Inoue@tpf.co.jp>
To: "Bruce Momjian" <pgman@candle.pha.pa.us>
Cc: "Tom Lane" <tgl@sss.pgh.pa.us>, "Jan Wieck" <JanWieck@yahoo.com>,
"PostgreSQL-development" <pgsql-hackers@postgreSQL.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>,
"Don Baccus" <dhogaza@pacifier.com>
Subject: RE: [HACKERS] Big 7.1 open items
Date: Tue, 20 Jun 2000 01:17:14 +0900
Message-ID: <EKEJJICOHDIEMGPNIFIJGECCCCAA.Inoue@tpf.co.jp>
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> -----Original Message-----
> From: Bruce Momjian [mailto:pgman@candle.pha.pa.us]
>
> The fact is that symlink information is already stored in the file
> system. If we store symlink information in the database too, there
> exists the ability for the two to get out of sync. My point is that I
> think we can _not_ store symlink information in the database, and query
> the file system using lstat when required.
>
Hmm,this seems pretty confusing to me.
I don't understand the necessity of symlink.
Directory tree,symlink,hard link ... are OS's standard.
But I don't think they are fit for dbms management.
PostgreSQL is a database system of cource. So
couldn't it handle more flexible structure than OS's
directory tree for itself ?
Regards.
Hiroshi Inoue
Inoue@tpf.co.jp
From Inoue@tpf.co.jp Tue Jun 20 02:01:04 2000
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From: "Hiroshi Inoue" <Inoue@tpf.co.jp>
To: "Bruce Momjian" <pgman@candle.pha.pa.us>
Cc: "Tom Lane" <tgl@sss.pgh.pa.us>, "Jan Wieck" <JanWieck@yahoo.com>,
"Ross J. Reedstrom" <reedstrm@rice.edu>,
"Don Baccus" <dhogaza@pacifier.com>,
"PostgreSQL-development" <pgsql-hackers@postgreSQL.org>
Subject: RE: [HACKERS] Big 7.1 open items
Date: Tue, 20 Jun 2000 14:52:17 +0900
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> -----Original Message-----
> From: Bruce Momjian [mailto:pgman@candle.pha.pa.us]
>
> > > -----Original Message-----
> > > From: Bruce Momjian [mailto:pgman@candle.pha.pa.us]
> > >
> > > The fact is that symlink information is already stored in the file
> > > system. If we store symlink information in the database too, there
> > > exists the ability for the two to get out of sync. My point is that I
> > > think we can _not_ store symlink information in the database,
> and query
> > > the file system using lstat when required.
> > >
> > Hmm,this seems pretty confusing to me.
> > I don't understand the necessity of symlink.
> > Directory tree,symlink,hard link ... are OS's standard.
> > But I don't think they are fit for dbms management.
> >
> > PostgreSQL is a database system of cource. So
> > couldn't it handle more flexible structure than OS's
> > directory tree for itself ?
>
> Yes, but is anyone suggesting a solution that does not work with
> symlinks? If not, why not do it that way?
>
Maybe other solutions have been proposed already because
there have been so many opinions and proposals.
I've felt TABLE(DATA)SPACE discussion has always been
divergent. IMHO,one of the main cause is that various factors
have been discussed at once. Shouldn't we make step by step
consensus in TABLE(DATA)SPACE discussion ?
IMHO,the first step is to decide the syntax of CREATE TABLE
command not to define TABLE(DATA)SPACE.
Comments ?
Regards.
Hiroshi Inoue
Inoue@tpf.co.jp
From tgl@sss.pgh.pa.us Tue Jun 20 10:51:32 2000
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To: Bruce Momjian <pgman@candle.pha.pa.us>
cc: Hiroshi Inoue <Inoue@tpf.co.jp>, Jan Wieck <JanWieck@yahoo.com>,
"Ross J. Reedstrom" <reedstrm@rice.edu>,
Don Baccus <dhogaza@pacifier.com>,
PostgreSQL-development <pgsql-hackers@postgreSQL.org>
Subject: Re: [HACKERS] Big 7.1 open items
In-reply-to: <200006201340.JAA10387@candle.pha.pa.us>
References: <200006201340.JAA10387@candle.pha.pa.us>
Comments: In-reply-to Bruce Momjian <pgman@candle.pha.pa.us>
message dated "Tue, 20 Jun 2000 09:40:03 -0400"
Date: Tue, 20 Jun 2000 10:36:04 -0400
Message-ID: <29686.961511764@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
Status: RO
Bruce Momjian <pgman@candle.pha.pa.us> writes:
> Agreed. Seems we have several issues:
> filename contents
> tablespace implementation
> tablespace directory layout
> tablespace commands and syntax
I think we've agreed that the filename must depend on tablespace,
file version, and file segment number in some fashion --- plus
the table name/OID of course. Although there's no real consensus
about exactly how to construct the name, agreeing on the components
is still a positive step.
A couple of other areas of contention were:
revising smgr interface to be cleaner
exactly what to store in pg_class
I don't think there's any quibble about the idea of cleaning up smgr,
but we don't have a complete proposal on the table yet either.
As for the pg_class issue, I still favor storing
(a) OID of tablespace --- not for file access, but so that
associated tablespace-table entry can be looked up
by tablespace management operations
(b) pathname of file as a column of type "name", including
a %d to be replaced by segment #
I think Peter was holding out for storing purely numeric tablespace OID
and table version in pg_class and having a hardwired mapping to pathname
somewhere in smgr. However, I think that doing it that way gains only
micro-efficiency compared to passing a "name" around, while using the
name approach buys us flexibility that's needed for at least some of
the variants under discussion. Given that the exact filename contents
are still so contentious, I think it'd be a bad idea to pick an
implementation that doesn't allow some leeway as to what the filename
will be. A name also has the advantage that it is a single item that
can be used to identify the table to smgr, which will help in cleaning
up the smgr interface.
As for tablespace layout/implementation, the only real proposal I've
heard is that there be a subdirectory of the database directory for each
tablespace, and that that have a subdirectory for each segment (extent)
of its tables --- where any of these subdirectories could be symlinks
off to a different filesystem. Some unhappiness was raised about
depending on symlinks for this function, but I didn't hear one single
concrete reason not to do it, nor an alternative design. Unless someone
comes up with a counterproposal, I think that that's what the actual
access mechanism will look like. We still need to talk about what we
want to store in the SQL-level representation of a tablespace, and what
sort of tablespace management tools/commands are needed. (Although
"try to make it look like Oracle" seems to be pretty much the consensus
for the command level, not all of us know exactly what that means...)
Comments? Anything else that we do have consensus on?
regards, tom lane
From pgsql-hackers-owner+M3615@hub.org Tue Jun 20 12:55:05 2000
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Date: Tue, 20 Jun 2000 18:43:35 +0200 (CEST)
From: Peter Eisentraut <peter_e@gmx.net>
To: Bruce Momjian <pgman@candle.pha.pa.us>
cc: Jan Wieck <JanWieck@Yahoo.com>, Tom Lane <tgl@sss.pgh.pa.us>,
Hiroshi Inoue <Inoue@tpf.co.jp>,
Bruce Momjian <maillist@candle.pha.pa.us>,
PostgreSQL-development <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: Re: [HACKERS] Big 7.1 open items
In-Reply-To: <200006180316.XAA15410@candle.pha.pa.us>
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Bruce Momjian writes:
> If we have a new CREATE DATABASE LOCATION command, we can say:
>
> CREATE DATABASE LOCATION dbloc IN '/var/private/pgsql';
> CREATE DATABASE newdb IN dbloc;
We kind of have this already, with CREATE DATABASE foo WITH LOCATION =
'bar'; but of course with environment variable kludgery. But it's a start.
> mkdir /var/private/pgsql/dbloc
> ln -s /var/private/pgsql/dbloc data/base/dbloc
I think the problem with this was that you'd have to do an extra lookup
into, say, pg_location to resolve this. Some people are talking about
blind writes, this is not really blind.
> CREATE LOCATION tabloc IN '/var/private/pgsql';
> CREATE TABLE newtab ... IN tabloc;
Okay, so we'd have "table spaces" and "database spaces". Seems like one
"space" ought to be enough. I was thinking that the database "space" would
serve as a default "space" for tables created within it but you could
still create tables in other "spaces" than were the database really is. In
fact, the database wouldn't show up at all in the file names anymore,
which may or may not be a good thing.
I think Tom suggested something more or less like this:
$PGDATA/base/tablespace/segment/table
(leaving the details of "table" aside for now). pg_class would get a
column storing the table space somehow, say an oid reference to
pg_location. There would have to be a default tablespace that's created by
initdb and it's indicated by oid 0. So if you create a simple little table
"foo" it ends up in
$PGDATA/base/0/0/foo
That is pretty manageable. Now to create a table space you do
CREATE LOCATION "name" AT '/some/where';
which would make an entry in pg_location and, similar to how you
suggested, create a symlink from
$PGDATA/base/newoid -> /some/where
Then when you create a new table at that new location this gets simply
noted in pg_class with an oid reference, the rest works completely
transparently and no lookup outside of pg_class required. The system would
create the segment 0 subdirectory automatically.
When tables get segmented the system would simply create subdirectories 1,
2, 3, etc. as needed, just as it created the 0 as need, no extra code.
pg_dump doesn't need to use lstat or whatever at all because the locations
are catalogued. Administrators don't even need to know about the linking
business, they just make sure the target directory exists.
Two more items to ponder:
* per-location transaction logs
* pg_upgrade
--
Peter Eisentraut Sernanders v<>g 10:115
peter_e@gmx.net 75262 Uppsala
http://yi.org/peter-e/ Sweden
From Inoue@tpf.co.jp Tue Jun 20 17:10:56 2000
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From: "Hiroshi Inoue" <Inoue@tpf.co.jp>
To: "Tom Lane" <tgl@sss.pgh.pa.us>, "Bruce Momjian" <pgman@candle.pha.pa.us>
Cc: "Jan Wieck" <JanWieck@yahoo.com>, "Ross J. Reedstrom" <reedstrm@rice.edu>,
"Don Baccus" <dhogaza@pacifier.com>,
"PostgreSQL-development" <pgsql-hackers@postgreSQL.org>
Subject: RE: [HACKERS] Big 7.1 open items
Date: Wed, 21 Jun 2000 05:59:41 +0900
Message-ID: <EKEJJICOHDIEMGPNIFIJIEDDCCAA.Inoue@tpf.co.jp>
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> -----Original Message-----
> From: Tom Lane [mailto:tgl@sss.pgh.pa.us]
>
> Bruce Momjian <pgman@candle.pha.pa.us> writes:
> > Agreed. Seems we have several issues:
>
> > filename contents
> > tablespace implementation
> > tablespace directory layout
> > tablespace commands and syntax
>
[snip]
>
> Comments? Anything else that we do have consensus on?
>
Before the details of tablespace implementation,
1) How to change(extend) the syntax of CREATE TABLE
We only add table(data)space name with some
keyword ? i.e Do we consider tablespace as an
abstraction ?
To confirm our mutual understanding.
2) Is tablespace defined per PostgreSQL's database ?
3) Is default tablespace defined per database/user or
for all ?
AFAIK in Oracle,2) global, 3) per user.
Regards.
Hiroshi Inoue
Inoue@tpf.co.jp
From Inoue@tpf.co.jp Tue Jun 20 20:00:59 2000
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From: "Hiroshi Inoue" <Inoue@tpf.co.jp>
To: "Peter Eisentraut" <peter_e@gmx.net>
Cc: "Jan Wieck" <JanWieck@Yahoo.com>, "Tom Lane" <tgl@sss.pgh.pa.us>,
"Bruce Momjian" <maillist@candle.pha.pa.us>,
"PostgreSQL-development" <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>,
"Bruce Momjian" <pgman@candle.pha.pa.us>
Subject: RE: [HACKERS] Big 7.1 open items
Date: Wed, 21 Jun 2000 08:54:51 +0900
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> -----Original Message-----
> From: Peter Eisentraut
>
> Bruce Momjian writes:
>
> > If we have a new CREATE DATABASE LOCATION command, we can say:
> >
> > CREATE DATABASE LOCATION dbloc IN '/var/private/pgsql';
> > CREATE DATABASE newdb IN dbloc;
>
> We kind of have this already, with CREATE DATABASE foo WITH LOCATION =
> 'bar'; but of course with environment variable kludgery. But it's a start.
>
> > mkdir /var/private/pgsql/dbloc
> > ln -s /var/private/pgsql/dbloc data/base/dbloc
>
> I think the problem with this was that you'd have to do an extra lookup
> into, say, pg_location to resolve this. Some people are talking about
> blind writes, this is not really blind.
>
> > CREATE LOCATION tabloc IN '/var/private/pgsql';
> > CREATE TABLE newtab ... IN tabloc;
>
> Okay, so we'd have "table spaces" and "database spaces". Seems like one
> "space" ought to be enough.
Does your "database space" correspond to current PostgreSQL's database ?
And is it different from SCHEMA ?
Regards.
Hiroshi Inoue
Inoue@tpf.co.jp
From tgl@sss.pgh.pa.us Wed Jun 21 00:23:48 2000
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To: Bruce Momjian <pgman@candle.pha.pa.us>
cc: Hiroshi Inoue <Inoue@tpf.co.jp>, Peter Eisentraut <peter_e@gmx.net>,
Jan Wieck <JanWieck@Yahoo.com>,
Bruce Momjian <maillist@candle.pha.pa.us>,
PostgreSQL-development <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: Re: [HACKERS] Big 7.1 open items
In-reply-to: <200006210345.XAA15107@candle.pha.pa.us>
References: <200006210345.XAA15107@candle.pha.pa.us>
Comments: In-reply-to Bruce Momjian <pgman@candle.pha.pa.us>
message dated "Tue, 20 Jun 2000 23:45:13 -0400"
Date: Wed, 21 Jun 2000 00:06:42 -0400
Message-ID: <2999.961560402@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
Status: ROr
Bruce Momjian <pgman@candle.pha.pa.us> writes:
> I recommend making a dbname in each directory, then putting the
> location inside there.
This still seems backwards to me. Why is it better than tablespace
directory inside database directory?
One significant problem with it is that there's no longer (AFAICS)
a "default" per-database directory that corresponds to the current
working directory of backends running in that database. Thus,
for example, it's not immediately clear where temporary files and
backend core-dump files will end up. Also, you've just added an
essential extra level (if not two) to the pathnames that backends will
use to address files.
There is a great deal to be said for
..../database/tablespace/filename
where .../database/ is the working directory of a backend running in
that database, so that the relative pathname used by that backend to
get to a table is just tablespace/filename. I fail to see any advantage
in reversing the pathname order. If you see one, enlighten me.
regards, tom lane
From pgsql-hackers-owner+M3635@hub.org Wed Jun 21 01:00:59 2000
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From: "Hiroshi Inoue" <Inoue@tpf.co.jp>
To: "Tom Lane" <tgl@sss.pgh.pa.us>, "Bruce Momjian" <pgman@candle.pha.pa.us>
Cc: "Peter Eisentraut" <peter_e@gmx.net>, "Jan Wieck" <JanWieck@Yahoo.com>,
"Bruce Momjian" <maillist@candle.pha.pa.us>,
"PostgreSQL-development" <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: RE: [HACKERS] Big 7.1 open items
Date: Wed, 21 Jun 2000 13:55:01 +0900
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> -----Original Message-----
> From: Tom Lane [mailto:tgl@sss.pgh.pa.us]
>
> Bruce Momjian <pgman@candle.pha.pa.us> writes:
> > I recommend making a dbname in each directory, then putting the
> > location inside there.
>
> This still seems backwards to me. Why is it better than tablespace
> directory inside database directory?
>
> One significant problem with it is that there's no longer (AFAICS)
> a "default" per-database directory that corresponds to the current
> working directory of backends running in that database. Thus,
> for example, it's not immediately clear where temporary files and
> backend core-dump files will end up. Also, you've just added an
> essential extra level (if not two) to the pathnames that backends will
> use to address files.
>
> There is a great deal to be said for
> ..../database/tablespace/filename
OK,I seem to have gotten the answer for the question
Is tablespace defined per PostgreSQL's database ?
You and Bruce
1) tablespace is per database
Peter seems to have the following idea(?? not sure)
2) database = tablespace
My opinion
3) database and tablespace are relatively irrelevant.
I assume PostgreSQL's database would correspond
to the concept of SCHEMA.
It seems we are different from the first.
Shoudln't we reach an agreement on it in the first place ?
Regards.
Hiroshi Inoue
Inoue@tpf.co.jp
From pgsql-hackers-owner+M3636@hub.org Wed Jun 21 01:31:12 2000
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To: Chris Bitmead <chrisb@nimrod.itg.telstra.com.au>
cc: Bruce Momjian <pgman@candle.pha.pa.us>,
PostgreSQL-development <pgsql-hackers@postgreSQL.org>
Subject: Re: [HACKERS] Big 7.1 open items
In-reply-to: <3950484D.417C87E9@nimrod.itg.telecom.com.au>
References: <200006210346.XAA15138@candle.pha.pa.us> <3950484D.417C87E9@nimrod.itg.telecom.com.au>
Comments: In-reply-to Chris Bitmead <chrisb@nimrod.itg.telstra.com.au>
message dated "Wed, 21 Jun 2000 14:45:01 +1000"
Date: Wed, 21 Jun 2000 01:09:52 -0400
Message-ID: <3459.961564192@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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Chris Bitmead <chrisb@nimrod.itg.telstra.com.au> writes:
> What I meant is, would you still be able to create tablespaces on
> systems without symlinks? That would seem to be a desirable feature.
All else being equal, it'd be nice. Since all else is not equal,
exactly how much sweat are we willing to expend on supporting that
feature on such systems --- to the exclusion of other features we
might expend the same sweat on, with more widely useful results?
Bear in mind that everything will still *work* just fine on such a
platform, you just don't have a way to spread the database across
multiple filesystems. That's only an issue if the platform has a
fairly Unixy notion of filesystems ... but no symlinks.
A few messages back someone was opining that we were wasting our time
thinking about tablespaces at all, because any modern platform can
create disk-spanning filesystems for itself, so applications don't have
to worry. I don't buy that argument in general, but I'm quite willing
to quote it for the *very* few systems that are Unixy enough to run
Postgres in the first place, but not quite Unixy enough to have
symlinks.
You gotta draw the line somewhere at what you will support, and
this particular line seems to me to be entirely reasonable and
justifiable. YMMV...
regards, tom lane
From dhogaza@pacifier.com Wed Jun 21 01:31:03 2000
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Date: Tue, 20 Jun 2000 22:12:48 -0700
To: "Philip J. Warner" <pjw@rhyme.com.au>, "Hiroshi Inoue" <Inoue@tpf.co.jp>,
"Tom Lane" <tgl@sss.pgh.pa.us>,
"Bruce Momjian" <pgman@candle.pha.pa.us>
From: Don Baccus <dhogaza@pacifier.com>
Subject: RE: [HACKERS] Big 7.1 open items
Cc: "Jan Wieck" <JanWieck@yahoo.com>, "Ross J. Reedstrom" <reedstrm@rice.edu>,
"PostgreSQL-development" <pgsql-hackers@postgreSQL.org>
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At 11:22 AM 6/21/00 +1000, Philip J. Warner wrote:
>It may be worth considering leaving the CREATE TABLE statement alone.
>Dec/RDB uses a new statement entirely to define where a table goes...
It's worth considering, but on the other hand Oracle users greatly
outnumber Compaq/RDB users these days...
If there's no SQL92 guidance for implementing a feature, I'm pretty much in
favor of tracking Oracle, whose SQL dialect is rapidly becoming a
de-facto standard.
I'm not saying I like the fact, Oracle's a pain in the ass. But when
adopting existing syntax, might as well adopt that of the crushing
borg.
- Don Baccus, Portland OR <dhogaza@pacifier.com>
Nature photos, on-line guides, Pacific Northwest
Rare Bird Alert Service and other goodies at
http://donb.photo.net.
From lockhart@alumni.caltech.edu Wed Jun 21 01:31:07 2000
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To: Bruce Momjian <pgman@candle.pha.pa.us>
Cc: Peter Eisentraut <peter_e@gmx.net>, Jan Wieck <JanWieck@yahoo.com>,
Tom Lane <tgl@sss.pgh.pa.us>, Hiroshi Inoue <Inoue@tpf.co.jp>,
Bruce Momjian <maillist@candle.pha.pa.us>,
PostgreSQL-development <pgsql-hackers@postgreSQL.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: Re: [HACKERS] Big 7.1 open items
References: <200006201753.NAA27293@candle.pha.pa.us>
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Status: ROr
> Yes, I didn't like the environment variable stuff. In fact, I would
> like to not mention the symlink location anywhere in the database, so
> it can be changed without changing it in the database.
Well, as y'all have noticed, I think there are strong reasons to use
environment variables to manage locations, and that symlinks are a
potential portability and robustness problem.
An additional point which has relevance to this whole discussion:
In the future we may allow system resource such as tables to carry names
which use multi-byte encodings. afaik these encodings are not allowed to
be used for physical file names, and even if they were the utility of
using standard operating system utilities like ls goes way down.
istm that from a portability and evolutionary standpoint OID-only file
names (or at least file names *not* based on relation/class names) is a
requirement.
Comments?
- Thomas
From tgl@sss.pgh.pa.us Wed Jun 21 01:31:05 2000
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To: "Hiroshi Inoue" <Inoue@tpf.co.jp>
cc: "Bruce Momjian" <pgman@candle.pha.pa.us>,
"Peter Eisentraut" <peter_e@gmx.net>, "Jan Wieck" <JanWieck@yahoo.com>,
"PostgreSQL-development" <pgsql-hackers@postgreSQL.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: Re: [HACKERS] Big 7.1 open items
In-reply-to: <000001bfdb3c$db728760$2801007e@tpf.co.jp>
References: <000001bfdb3c$db728760$2801007e@tpf.co.jp>
Comments: In-reply-to "Hiroshi Inoue" <Inoue@tpf.co.jp>
message dated "Wed, 21 Jun 2000 13:55:01 +0900"
Date: Wed, 21 Jun 2000 01:23:57 -0400
Message-ID: <3554.961565037@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
Status: ROr
"Hiroshi Inoue" <Inoue@tpf.co.jp> writes:
>> There is a great deal to be said for
>> ..../database/tablespace/filename
> OK,I seem to have gotten the answer for the question
> Is tablespace defined per PostgreSQL's database ?
Not necessarily --- the tablespace subdirectories could be symlinks
pointing to the same place (assuming you use OIDs or something to keep
the table filenames unique even across databases). This is just an
implementation mechanism; it doesn't foreclose the policy decision
whether tablespaces are database-local or installation-wide.
(OTOH, pathnames like tablespace/database would pretty much force
tablespaces to be installation-wide whether you wanted it that way
or not.)
> My opinion
> 3) database and tablespace are relatively irrelevant.
> I assume PostgreSQL's database would correspond
> to the concept of SCHEMA.
My inclindation is that tablespaces should be installation-wide, but
I'm not completely sold on it. In any case I could see wanting a
permissions mechanism that would only allow some databases to have
tables in a particular tablespace.
We do need to think more about how traditional Postgres databases
fit together with SCHEMA. Maybe we wouldn't even need multiple
databases per installation if we had SCHEMA done right.
regards, tom lane
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Date: Wed, 21 Jun 2000 00:45:02 -0500
From: "Ross J. Reedstrom" <reedstrm@rice.edu>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Hiroshi Inoue <Inoue@tpf.co.jp>, Bruce Momjian <pgman@candle.pha.pa.us>,
Peter Eisentraut <peter_e@gmx.net>, Jan Wieck <JanWieck@yahoo.com>,
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Subject: Re: [HACKERS] Big 7.1 open items
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References: <000001bfdb3c$db728760$2801007e@tpf.co.jp> <3554.961565037@sss.pgh.pa.us>
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On Wed, Jun 21, 2000 at 01:23:57AM -0400, Tom Lane wrote:
> "Hiroshi Inoue" <Inoue@tpf.co.jp> writes:
>
> > My opinion
> > 3) database and tablespace are relatively irrelevant.
> > I assume PostgreSQL's database would correspond
> > to the concept of SCHEMA.
>
> My inclindation is that tablespaces should be installation-wide, but
> I'm not completely sold on it. In any case I could see wanting a
> permissions mechanism that would only allow some databases to have
> tables in a particular tablespace.
>
> We do need to think more about how traditional Postgres databases
> fit together with SCHEMA. Maybe we wouldn't even need multiple
> databases per installation if we had SCHEMA done right.
>
The important point I think is that tablespaces are about physical
storage/namespace, and SCHEMA are about logical namespace: it would make
sense for tables from multiple schema to live in the same tablespace,
as well as tables from one schema to be stored in multiple tablespaces.
Ross
--
Ross J. Reedstrom, Ph.D., <reedstrm@rice.edu>
NSBRI Research Scientist/Programmer
Computer and Information Technology Institute
Rice University, 6100 S. Main St., Houston, TX 77005
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Date: Wed, 21 Jun 2000 16:13:47 +1000
From: Chris Bitmead <chrisb@nimrod.itg.telstra.com.au>
Organization: IBM Global Services
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To: PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: [HACKERS] Big 7.1 open items
References: <000001bfdb3c$db728760$2801007e@tpf.co.jp> <3554.961565037@sss.pgh.pa.us> <20000621004502.A24387@rice.edu>
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"Ross J. Reedstrom" wrote:
> The important point I think is that tablespaces are about physical
> storage/namespace, and SCHEMA are about logical namespace: it would make
> sense for tables from multiple schema to live in the same tablespace,
> as well as tables from one schema to be stored in multiple tablespaces.
If we accept that argument (which sounds good) then wouldn't we have...
data/base/db1/table1 -> ../../../tablespace/ts1/db1.table1
data/base/db1/table2 -> ../../../tablespace/ts1/db1.table2
data/tablespace/ts1/db1.table1
data/tablespace/ts1/db1.table2
In other words there is a directory for databases, and a directory for
tablespaces. Database tables are symlinked to the appropriate
tablespace. So there is multiple databases per tablespace and multiple
tablespaces per database.
From pgsql-hackers-owner+M3648@hub.org Wed Jun 21 09:01:01 2000
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From: Zeugswetter Andreas SB <ZeugswetterA@wien.spardat.at>
To: "'Hiroshi Inoue'" <Inoue@tpf.co.jp>
Cc: "'pgsql-hackers@postgresql.org'" <pgsql-hackers@postgresql.org>
Subject: AW: [HACKERS] Big 7.1 open items
Date: Wed, 21 Jun 2000 14:48:43 +0200
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> > > CREATE LOCATION tabloc IN '/var/private/pgsql';
> > > CREATE TABLE newtab ... IN tabloc;
> >
> > Okay, so we'd have "table spaces" and "database spaces".
> Seems like one
> > "space" ought to be enough.
Yes, one space should be enough.
>
> Does your "database space" correspond to current PostgreSQL's
> database ?
I think we should think of the "database space" as the default "table space"
for this database.
> And is it different from SCHEMA ?
Please don't mix schema and database, they are two different issues.
Even Oracle has a database, only in Oracle you are limited to one database
per instance. We do not want to add this limitation to PostgreSQL.
Andreas
From e99re41@DoCS.UU.SE Wed Jun 21 10:01:10 2000
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From: Peter Eisentraut <e99re41@DoCS.UU.SE>
Reply-To: Peter Eisentraut <peter_e@gmx.net>
To: Hiroshi Inoue <Inoue@tpf.co.jp>
cc: Tom Lane <tgl@sss.pgh.pa.us>, Bruce Momjian <pgman@candle.pha.pa.us>,
Jan Wieck <JanWieck@yahoo.com>,
Bruce Momjian <maillist@candle.pha.pa.us>,
PostgreSQL-development <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: RE: [HACKERS] Big 7.1 open items
In-Reply-To: <000001bfdb3c$db728760$2801007e@tpf.co.jp>
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On Wed, 21 Jun 2000, Hiroshi Inoue wrote:
> Peter seems to have the following idea(?? not sure)
> 2) database = tablespace
No, I thought that a database would have a table space assigned that would
serve as the default for newly created tables, but could be overridden. So
you could group databases onto disks as you want, but a couple of
particularly big/important/unimportant/etc tables from each database could
be put on a different disk. At least this seems to be the most flexible
and conceptually simple solution.
Ideally, directories per database would go away, but then we'd have the
system tables colliding, since those have the same oid in each database.
But that's not really important. So essentially you'd have
$PGDATA/base/tablespacesomething/database/tables
In the default tablespace, "tablespacesomething" is an ordinary directory,
for other tablespaces it symlinks somewhere else. For those browsing
$PGDATA/base, it all looks the same (unless you have colour ls). For those
browsing the actual storage location it looks like
/var/foo/elsewhere/database/tables.
I'm sure you can squeeze the extension segments in there, maybe between
tablespace and database.
What I think Bruce is saying is that there should be both database spaces
and table spaces, I think that's too much.
> My opinion
> 3) database and tablespace are relatively irrelevant.
> I assume PostgreSQL's database would correspond
> to the concept of SCHEMA.
A database corresponds to a catalog and a schema corresponds to nothing
yet.
--
Peter Eisentraut Sernanders v<>g 10:115
peter_e@gmx.net 75262 Uppsala
http://yi.org/peter-e/ Sweden
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From: Peter Eisentraut <e99re41@DoCS.UU.SE>
Reply-To: Peter Eisentraut <peter_e@gmx.net>
To: Bruce Momjian <pgman@candle.pha.pa.us>
cc: Jan Wieck <JanWieck@yahoo.com>, Tom Lane <tgl@sss.pgh.pa.us>,
Hiroshi Inoue <Inoue@tpf.co.jp>,
Bruce Momjian <maillist@candle.pha.pa.us>,
PostgreSQL-development <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: Re: [HACKERS] Big 7.1 open items
In-Reply-To: <200006201753.NAA27293@candle.pha.pa.us>
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On Tue, 20 Jun 2000, Bruce Momjian wrote:
> What I was suggesting is not to catalog the symlink locations, but to
> use lstat when dumping, so that admins can move files around using
> symlinks and not have to udpate the database.
That surely wouldn't make those happy that are calling for smgr
abstraction.
--
Peter Eisentraut Sernanders v<>g 10:115
peter_e@gmx.net 75262 Uppsala
http://yi.org/peter-e/ Sweden
From tgl@sss.pgh.pa.us Wed Jun 21 11:31:09 2000
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To: Bruce Momjian <pgman@candle.pha.pa.us>
cc: Hiroshi Inoue <Inoue@tpf.co.jp>, Peter Eisentraut <peter_e@gmx.net>,
Jan Wieck <JanWieck@Yahoo.com>,
Bruce Momjian <maillist@candle.pha.pa.us>,
PostgreSQL-development <pgsql-hackers@postgreSQL.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: Re: [HACKERS] Big 7.1 open items
In-reply-to: <200006210433.AAA18343@candle.pha.pa.us>
References: <200006210433.AAA18343@candle.pha.pa.us>
Comments: In-reply-to Bruce Momjian <pgman@candle.pha.pa.us>
message dated "Wed, 21 Jun 2000 00:33:01 -0400"
Date: Wed, 21 Jun 2000 11:07:20 -0400
Message-ID: <4283.961600040@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
Status: ROr
Bruce Momjian <pgman@candle.pha.pa.us> writes:
> Yes, agreed. I was thinking this:
> CREATE TABLESPACE loc USING '/var/pgsql'
> does:
> ln -s /var/pgsql/dbname/loc data/base/dbname/loc
> In this way, the database has a view of its main directory, plus a /loc
> subdirectory for the tablespace. In the other location, we have
> /var/pgsql/dbname/loc because this allows different databases to use:
> CREATE TABLESPACE loc USING '/var/pgsql'
> and they do not collide with each other in /var/pgsql.
But they don't collide anyway, because the dbname is already unique.
Isn't the extra subdirectory a waste?
Because table files will have installation-wide unique names, there's
no really good reason to have either level of subdirectory; you could
just make
CREATE TABLESPACE loc USING '/var/pgsql'
do
ln -s /var/pgsql data/base/dbname/loc
and it'd still work even if multiple DBs were using the same tablespace.
However, forcing creation of a subdirectory does give you the chance to
make sure the subdir is owned by postgres and has the right permissions,
so there's something to be said for that. It might be reasonable to do
mkdir /var/pgsql/dbname
chmod 700 /var/pgsql/dbname
ln -s /var/pgsql/dbname data/base/dbname/loc
regards, tom lane
From lockhart@alumni.caltech.edu Wed Jun 21 11:31:10 2000
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From: Thomas Lockhart <lockhart@alumni.caltech.edu>
Organization: Yes
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To: Bruce Momjian <pgman@candle.pha.pa.us>
Cc: Peter Eisentraut <peter_e@gmx.net>, Jan Wieck <JanWieck@Yahoo.com>,
Tom Lane <tgl@sss.pgh.pa.us>, Hiroshi Inoue <Inoue@tpf.co.jp>,
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PostgreSQL-development <pgsql-hackers@postgreSQL.org>,
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Subject: Re: [HACKERS] Big 7.1 open items
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> Sorry, disagree. Environment variables are a pain to administer, and
> quite counter-intuitive.
Well, I guess we disagree. But until we have a complete proposed
solution, we should leave environment variables on the table, since they
*do* allow some decoupling of logical and physical storage, and *do*
give the administrator some control over resources *that the admin would
not otherwise have*.
> > istm that from a portability and evolutionary standpoint OID-only
> > file names (or at least file names *not* based on relation/class
> > names) is a requirement.
> Maybe a requirement at some point for some installations, but I hope
> not a general requirement.
If a table name can have characters which are not legal for file names,
then how would you propose to support it? If we are doing a
restructuring of the storage scheme, this should be taken into account.
lockhart=# create table "one/two" (i int);
ERROR: cannot create one/two
Why not? It demonstrates an unfortunate linkage between file systems and
database resources.
- Thomas
From tgl@sss.pgh.pa.us Wed Jun 21 11:31:18 2000
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To: Thomas Lockhart <lockhart@alumni.caltech.edu>
cc: Bruce Momjian <pgman@candle.pha.pa.us>, Peter Eisentraut <peter_e@gmx.net>,
Jan Wieck <JanWieck@Yahoo.com>, Hiroshi Inoue <Inoue@tpf.co.jp>,
Bruce Momjian <maillist@candle.pha.pa.us>,
PostgreSQL-development <pgsql-hackers@postgreSQL.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: Re: [HACKERS] Big 7.1 open items
In-reply-to: <39505061.F42334AB@alumni.caltech.edu>
References: <200006201753.NAA27293@candle.pha.pa.us> <39505061.F42334AB@alumni.caltech.edu>
Comments: In-reply-to Thomas Lockhart <lockhart@alumni.caltech.edu>
message dated "Wed, 21 Jun 2000 05:19:29 -0000"
Date: Wed, 21 Jun 2000 11:28:09 -0400
Message-ID: <4448.961601289@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
Status: RO
Thomas Lockhart <lockhart@alumni.caltech.edu> writes:
> Well, as y'all have noticed, I think there are strong reasons to use
> environment variables to manage locations, and that symlinks are a
> potential portability and robustness problem.
Reasons? Evidence?
> An additional point which has relevance to this whole discussion:
> In the future we may allow system resource such as tables to carry names
> which use multi-byte encodings. afaik these encodings are not allowed to
> be used for physical file names, and even if they were the utility of
> using standard operating system utilities like ls goes way down.
Good point, although in one sense a string is a string --- as long as
we don't allow embedded nulls in server-side encodings, we could use
anything that Postgres thought was a name in a filename, and the OS
should take it. But if your local ls doesn't show it the way you see
in Postgres, the usefulness of having the tablename in the filename
goes way down.
> istm that from a portability and evolutionary standpoint OID-only file
> names (or at least file names *not* based on relation/class names) is a
> requirement.
No argument from me ;-). I've been looking for compromise positions
but I still think that pure numeric filenames are the cleanest solution.
There's something else that should be taken into account: for WAL, the
log will need to record the table file that each insert/delete/update
operation affects. To do that with the smgr-token-is-a-pathname
approach I was suggesting yesterday, I think you have to record the
database name and pathname in each WAL log entry. That's 64 bytes/log
entry which is a *lot*. If we bit the bullet and restricted ourselves
to numeric filenames then the log would need just four numeric values:
database OID
tablespace OID
relation OID
relation version number
(this set of 4 values would also be an smgr file reference token).
16 bytes/log entry looks much better than 64.
At the moment I can recall the following opinions:
Pure OID filenames: Thomas, Tom, Marc, Peter E.
OID+relname filenames: Bruce
Vadim was in the pure-OID camp a few months ago, but I won't presume
to list him there now since he hasn't been involved in this most
recent round of discussions. I'm not sure where anyone else stands...
but at least in terms of the core group it's pretty clear where the
majority opinion is.
regards, tom lane
From lamar.owen@wgcr.org Wed Jun 21 11:51:39 2000
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Message-ID: <3950E3C3.7322BD70@wgcr.org>
Date: Wed, 21 Jun 2000 11:48:19 -0400
From: Lamar Owen <lamar.owen@wgcr.org>
X-Mailer: Mozilla 4.61 [en] (Win95; I)
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To: Tom Lane <tgl@sss.pgh.pa.us>
CC: Thomas Lockhart <lockhart@alumni.caltech.edu>,
Bruce Momjian <pgman@candle.pha.pa.us>,
Peter Eisentraut <peter_e@gmx.net>, Jan Wieck <JanWieck@Yahoo.com>,
Hiroshi Inoue <Inoue@tpf.co.jp>,
Bruce Momjian <maillist@candle.pha.pa.us>,
PostgreSQL-development <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: Re: [HACKERS] Big 7.1 open items
References: <200006201753.NAA27293@candle.pha.pa.us> <39505061.F42334AB@alumni.caltech.edu> <4448.961601289@sss.pgh.pa.us>
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
Status: ROr
Tom Lane wrote:
> Thomas Lockhart <lockhart@alumni.caltech.edu> writes:
> > Well, as y'all have noticed, I think there are strong reasons to use
> > environment variables to manage locations, and that symlinks are a
> > potential portability and robustness problem.
> Reasons? Evidence?
Does Win32 do symlinks these days? I know Win32 does envvars, and Win32
is currently a supported platform.
I'm not thrilled with either solution -- envvars have their problems
just as surely as symlinks do.
> At the moment I can recall the following opinions:
> Pure OID filenames: Thomas, Tom, Marc, Peter E.
FWIW, count me here. I have tried administering my system using the
filenames -- and have been bitten. Better admin tools in the PostgreSQL
package beat using standard filesystem tools -- the PostgreSQL tools can
be WAL-aware, transaction-aware, and can provide consistent results.
Filesystem tools never will be able to provide consistent results for a
database system that must remain up 24x7, as many if not most PostgreSQL
installations must.
> OID+relname filenames: Bruce
Sorry Bruce -- I understand and am sympathetic to your position, and, at
one time, I agreed with it. But not any more.
--
Lamar Owen
WGCR Internet Radio
1 Peter 4:11
From tgl@sss.pgh.pa.us Wed Jun 21 12:10:06 2000
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To: Bruce Momjian <pgman@candle.pha.pa.us>
cc: Hiroshi Inoue <Inoue@tpf.co.jp>, Peter Eisentraut <peter_e@gmx.net>,
Jan Wieck <JanWieck@Yahoo.com>,
PostgreSQL-development <pgsql-hackers@postgreSQL.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: Re: [HACKERS] Big 7.1 open items
In-reply-to: <200006211545.LAA08773@candle.pha.pa.us>
References: <200006211545.LAA08773@candle.pha.pa.us>
Comments: In-reply-to Bruce Momjian <pgman@candle.pha.pa.us>
message dated "Wed, 21 Jun 2000 11:45:12 -0400"
Date: Wed, 21 Jun 2000 12:10:15 -0400
Message-ID: <4786.961603815@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
Status: ROr
Bruce Momjian <pgman@candle.pha.pa.us> writes:
> Yes, that is true. My idea is that they may want to create loc1 and
> loc2 which initially point to the same location, but later may be moved.
> For example, one tablespace for tables, another for indexes. They may
> initially point to the same directory, but later be split.
Well, that opens up a completely different issue, which is what about
moving tables from one tablespace to another?
I think the way you appear to be implying above (shut down the server
so that you can rearrange subdirectories by hand) is the wrong way to
go about it. For one thing, lots of people don't want to shut down
their servers completely for that long, but it's difficult to avoid
doing so if you want to move files by filesystem commands. For another
thing, the above approach requires guessing in advance --- maybe long
in advance --- how you are going to want to repartition your database
when it gets too big for your existing storage.
The right way to address this problem is to invent a "move table to
new tablespace" command. This'd be pretty trivial to implement based
on a file-versioning approach: the new version of the pg_class tuple
has a new tablespace identifier in it.
regards, tom lane
From pgsql-hackers-owner+M3670@hub.org Wed Jun 21 12:30:42 2000
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To: Bruce Momjian <pgman@candle.pha.pa.us>
cc: Lamar Owen <lamar.owen@wgcr.org>,
Thomas Lockhart <lockhart@alumni.caltech.edu>,
Peter Eisentraut <peter_e@gmx.net>, Jan Wieck <JanWieck@Yahoo.com>,
Hiroshi Inoue <Inoue@tpf.co.jp>,
PostgreSQL-development <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: Re: [HACKERS] Big 7.1 open items
In-reply-to: <200006211603.MAA09414@candle.pha.pa.us>
References: <200006211603.MAA09414@candle.pha.pa.us>
Comments: In-reply-to Bruce Momjian <pgman@candle.pha.pa.us>
message dated "Wed, 21 Jun 2000 12:03:12 -0400"
Date: Wed, 21 Jun 2000 12:17:37 -0400
Message-ID: <4875.961604257@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
X-Mailing-List: pgsql-hackers@postgresql.org
Precedence: bulk
Sender: pgsql-hackers-owner@hub.org
Status: RO
Bruce Momjian <pgman@candle.pha.pa.us> writes:
>> Sorry Bruce -- I understand and am sympathetic to your position, and, at
>> one time, I agreed with it. But not any more.
> I thought the most recent proposal was to just throw ~16 chars of the
> file name on the end of the file name, and that should not be used for
> anything except visibility. WAL would not need to store that. It could
> just grab the file name that matches the oid/sequence number.
But that's extra complexity in WAL, plus extra complexity in renaming
tables (if you want the filename to track the logical table name, which
I expect you would), plus extra complexity in smgr and bufmgr and other
places.
I think people are coming around to the notion that it's better to keep
these low-level operations simple, even if we need to expend more work
on high-level admin tools as a result.
But we do need to remember to expend that effort on tools! Let's not
drop the ball on that, folks.
regards, tom lane
From tgl@sss.pgh.pa.us Wed Jun 21 12:30:40 2000
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To: Bruce Momjian <pgman@candle.pha.pa.us>
cc: Hiroshi Inoue <Inoue@tpf.co.jp>, Peter Eisentraut <peter_e@gmx.net>,
Jan Wieck <JanWieck@Yahoo.com>,
PostgreSQL-development <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: Re: [HACKERS] Big 7.1 open items
In-reply-to: <200006211614.MAA09938@candle.pha.pa.us>
References: <200006211614.MAA09938@candle.pha.pa.us>
Comments: In-reply-to Bruce Momjian <pgman@candle.pha.pa.us>
message dated "Wed, 21 Jun 2000 12:14:59 -0400"
Date: Wed, 21 Jun 2000 12:24:44 -0400
Message-ID: <4941.961604684@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
Status: ROr
Bruce Momjian <pgman@candle.pha.pa.us> writes:
>> Well, that opens up a completely different issue, which is what about
>> moving tables from one tablespace to another?
> Are you suggesting that doing dbname/locname is somehow harder to do
> that? If you are, I don't understand why.
It doesn't make it harder, but it still seems pointless to have the
extra directory level. Bear in mind that if we go with all-OID
filenames then you're not going to be looking at "loc1" and "loc2"
anyway, but at "5938171" and "8583727". It's not much of a convenience
to the admin to see that, so we might as well save a level of directory
lookup.
> The general issue of moving tables between tablespaces can be done from
> in the database. I don't think it is reasonable to shut down the db to
> do that. However, I can see moving tablespaces to different symlinked
> locations may require a shutdown.
Only if you insist on doing it outside the database using filesystem
tools. Another way is to create a new tablespace in the desired new
location, then move the tables one-by-one to that new tablespace.
I suppose either one might be preferable depending on your access
patterns --- locking your most critical tables while they're being moved
might be as bad as a total shutdown.
regards, tom lane
From tgl@sss.pgh.pa.us Wed Jun 21 13:01:06 2000
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Wed, 21 Jun 2000 12:46:34 -0400 (EDT)
To: Bruce Momjian <pgman@candle.pha.pa.us>
cc: Hiroshi Inoue <Inoue@tpf.co.jp>, Peter Eisentraut <peter_e@gmx.net>,
Jan Wieck <JanWieck@Yahoo.com>,
PostgreSQL-development <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: Re: [HACKERS] Big 7.1 open items
In-reply-to: <200006211640.MAA10498@candle.pha.pa.us>
References: <200006211640.MAA10498@candle.pha.pa.us>
Comments: In-reply-to Bruce Momjian <pgman@candle.pha.pa.us>
message dated "Wed, 21 Jun 2000 12:40:35 -0400"
Date: Wed, 21 Jun 2000 12:46:34 -0400
Message-ID: <5109.961605994@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
Status: ROr
Bruce Momjian <pgman@candle.pha.pa.us> writes:
>>>> Are you suggesting that doing dbname/locname is somehow harder to do
>>>> that? If you are, I don't understand why.
>>
>> It doesn't make it harder, but it still seems pointless to have the
>> extra directory level. Bear in mind that if we go with all-OID
>> filenames then you're not going to be looking at "loc1" and "loc2"
>> anyway, but at "5938171" and "8583727". It's not much of a convenience
>> to the admin to see that, so we might as well save a level of directory
>> lookup.
> Just seems easier to have stuff segregates into separate per-db
> directories for clarity. Also, as directories get bigger, finding a
> specific file in there becomes harder. Putting 10 databases all in the
> same directory seems bad in this regard.
Huh? I wasn't arguing against making a db-specific directory below the
tablespace point. I was arguing against making *another* directory
below that one.
> I don't think we want to be using
> symlinks for tables if we can avoid it.
Agreed, but where did that come from? None of these proposals mentioned
symlinks for anything but directories, AFAIR.
regards, tom lane
From peter@localhost.its.uu.se Wed Jun 21 14:31:13 2000
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Date: Wed, 21 Jun 2000 20:16:10 +0200 (CEST)
From: Peter Eisentraut <peter_e@gmx.net>
To: Tom Lane <tgl@sss.pgh.pa.us>
cc: Bruce Momjian <pgman@candle.pha.pa.us>, Hiroshi Inoue <Inoue@tpf.co.jp>,
Jan Wieck <JanWieck@yahoo.com>,
"Ross J. Reedstrom" <reedstrm@rice.edu>,
Don Baccus <dhogaza@pacifier.com>,
PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: [HACKERS] Big 7.1 open items
In-Reply-To: <29686.961511764@sss.pgh.pa.us>
Message-ID: <Pine.LNX.4.21.0006201906100.4054-100000@localhost.localdomain>
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=ISO-8859-1
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Sender: Peter Eisentraut <peter@Op.Net>
Status: ROr
Tom Lane writes:
> I think Peter was holding out for storing purely numeric tablespace OID
> and table version in pg_class and having a hardwired mapping to pathname
> somewhere in smgr. However, I think that doing it that way gains only
> micro-efficiency compared to passing a "name" around, while using the
> name approach buys us flexibility that's needed for at least some of
> the variants under discussion.
But that name can only be a dozen or so characters, contain no slash or
other funny characters, etc. That's really poor. Then the alternative is
to have an internal name and an external canonical name. Then you have two
names to worry about. Also consider that when you store both the table
space oid and the internal name in pg_class you create redundant data.
What if you rename the table space? Do you leave the internal name out of
sync? Then what good is the internal name? I'm just concerned that we are
creating at the table space level problems similar to that we're trying to
get rid of at the relation and database level.
--
Peter Eisentraut Sernanders v<>g 10:115
peter_e@gmx.net 75262 Uppsala
http://yi.org/peter-e/ Sweden
From tgl@sss.pgh.pa.us Wed Jun 21 18:14:19 2000
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Wed, 21 Jun 2000 17:39:38 -0400 (EDT)
To: Bruce Momjian <pgman@candle.pha.pa.us>
cc: Peter Eisentraut <peter_e@gmx.net>, Hiroshi Inoue <Inoue@tpf.co.jp>,
Jan Wieck <JanWieck@yahoo.com>,
"Ross J. Reedstrom" <reedstrm@rice.edu>,
Don Baccus <dhogaza@pacifier.com>,
PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: [HACKERS] Big 7.1 open items
In-reply-to: <200006211842.OAA13514@candle.pha.pa.us>
References: <200006211842.OAA13514@candle.pha.pa.us>
Comments: In-reply-to Bruce Momjian <pgman@candle.pha.pa.us>
message dated "Wed, 21 Jun 2000 14:42:21 -0400"
Date: Wed, 21 Jun 2000 17:39:38 -0400
Message-ID: <6028.961623578@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
Status: RO
Bruce Momjian <pgman@candle.pha.pa.us> writes:
>> But that name can only be a dozen or so characters, contain no slash or
>> other funny characters, etc. That's really poor. Then the alternative is
>> to have an internal name and an external canonical name. Then you have two
>> names to worry about. Also consider that when you store both the table
>> space oid and the internal name in pg_class you create redundant data.
>> What if you rename the table space? Do you leave the internal name out of
>> sync? Then what good is the internal name? I'm just concerned that we are
>> creating at the table space level problems similar to that we're trying to
>> get rid of at the relation and database level.
> Agreed. Having table spaces stored by directories named by oid just
> seems very complicated for no reason.
Huh? He just gave you two very good reasons: avoid Unix-derived
limitations on the naming of tablespaces (and tables), and avoid
problems with renaming tablespaces.
I'm pretty much firmly back in the "OID and nothing but" camp.
Or perhaps I should say "OID, file version, and nothing but",
since we still need a version number to do CLUSTER etc.
regards, tom lane
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From: "Mikheev, Vadim" <vmikheev@SECTORBASE.COM>
To: "'Tom Lane'" <tgl@sss.pgh.pa.us>,
Thomas Lockhart
<lockhart@alumni.caltech.edu>
Cc: Bruce Momjian <pgman@candle.pha.pa.us>,
Peter Eisentraut
<peter_e@gmx.net>, Jan Wieck <JanWieck@Yahoo.com>,
Hiroshi Inoue
<Inoue@tpf.co.jp>,
Bruce Momjian <maillist@candle.pha.pa.us>,
PostgreSQL-development <pgsql-hackers@postgreSQL.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: RE: [HACKERS] Big 7.1 open items
Date: Wed, 21 Jun 2000 16:00:17 -0700
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> If we bit the bullet and restricted ourselves to numeric filenames then
> the log would need just four numeric values:
> database OID
> tablespace OID
Is someone going to implement it for 7.1?
> relation OID
> relation version number
I believe that we can avoid versions using WAL...
> (this set of 4 values would also be an smgr file reference token).
> 16 bytes/log entry looks much better than 64.
>
> At the moment I can recall the following opinions:
>
> Pure OID filenames: Thomas, Tom, Marc, Peter E.
+ me.
But what about LOCATIONs? I object using environment and think that
locations
must be stored in pg_control..?
Vadim
From Inoue@tpf.co.jp Wed Jun 21 22:18:39 2000
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From: "Hiroshi Inoue" <Inoue@tpf.co.jp>
To: "Tom Lane" <tgl@sss.pgh.pa.us>
Cc: "Bruce Momjian" <pgman@candle.pha.pa.us>,
"Peter Eisentraut" <peter_e@gmx.net>, "Jan Wieck" <JanWieck@Yahoo.com>,
"Bruce Momjian" <maillist@candle.pha.pa.us>,
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Subject: RE: [HACKERS] Big 7.1 open items
Date: Thu, 22 Jun 2000 08:37:42 +0900
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> -----Original Message-----
> From: Tom Lane [mailto:tgl@sss.pgh.pa.us]
>
> No argument from me ;-). I've been looking for compromise positions
> but I still think that pure numeric filenames are the cleanest solution.
>
> There's something else that should be taken into account: for WAL, the
> log will need to record the table file that each insert/delete/update
> operation affects. To do that with the smgr-token-is-a-pathname
> approach I was suggesting yesterday, I think you have to record the
> database name and pathname in each WAL log entry. That's 64 bytes/log
> entry which is a *lot*. If we bit the bullet and restricted ourselves
> to numeric filenames then the log would need just four numeric values:
> database OID
> tablespace OID
I strongly object to keep tablespace OID for smgr file reference token
though we have to keep it for another purpose of cource. I've mentioned
many times tablespace(where to store) info should be distinguished from
*where it is stored* info. Generally tablespace isn't sufficiently
restrictive
for this purpose. e.g. there was an idea about round-robin. e.g. Oracle's
tablespace could have pluaral files... etc.
IMHO,it is misleading to use tablespace OID as (a part of) reference token.
> relation OID
> relation version number
> (this set of 4 values would also be an smgr file reference token).
> 16 bytes/log entry looks much better than 64.
>
Regards.
Hiroshi Inoue
Inoue@tpf.co.jp
From Inoue@tpf.co.jp Wed Jun 21 22:18:15 2000
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From: "Hiroshi Inoue" <Inoue@tpf.co.jp>
To: "Mikheev, Vadim" <vmikheev@SECTORBASE.COM>
Cc: "Bruce Momjian" <pgman@candle.pha.pa.us>,
"Peter Eisentraut" <peter_e@gmx.net>, "Jan Wieck" <JanWieck@Yahoo.com>,
"Bruce Momjian" <maillist@candle.pha.pa.us>,
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Subject: RE: [HACKERS] Big 7.1 open items
Date: Thu, 22 Jun 2000 09:16:30 +0900
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Status: RO
> -----Original Message-----
> From: Mikheev, Vadim [mailto:vmikheev@SECTORBASE.COM]
>
> > If we bit the bullet and restricted ourselves to numeric filenames then
> > the log would need just four numeric values:
> > database OID
> > tablespace OID
>
> Is someone going to implement it for 7.1?
>
> > relation OID
> > relation version number
>
> I believe that we can avoid versions using WAL...
>
How to re-construct tables in place ?
Is the following right ?
1) save the content of current table to somewhere
2) shrink the table and related indexes
3) reload the saved(+some filtering) content
Regards.
Hiroshi Inoue
Inoue@tpf.co.jp
From Inoue@tpf.co.jp Wed Jun 21 22:18:16 2000
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From: "Hiroshi Inoue" <Inoue@tpf.co.jp>
To: "Mikheev, Vadim" <vmikheev@SECTORBASE.COM>
Cc: "Bruce Momjian" <pgman@candle.pha.pa.us>,
"Peter Eisentraut" <peter_e@gmx.net>, "Jan Wieck" <JanWieck@Yahoo.com>,
"Bruce Momjian" <maillist@candle.pha.pa.us>,
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Subject: RE: [HACKERS] Big 7.1 open items
Date: Thu, 22 Jun 2000 09:45:46 +0900
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> -----Original Message-----
> From: Mikheev, Vadim [mailto:vmikheev@SECTORBASE.COM]
>
> > > > relation version number
> > >
> > > I believe that we can avoid versions using WAL...
> > >
> >
> > How to re-construct tables in place ?
> > Is the following right ?
> > 1) save the content of current table to somewhere
> > 2) shrink the table and related indexes
> > 3) reload the saved(+some filtering) content
>
> Or - create tmp file and load with new content; log "intent to
> relink table
> file";
> relink table file; log "file is relinked".
>
It seems to me that whole content of the table should be
logged before relinking or shrinking.
Is my understanding right ?
Regards.
Hiroshi Inoue
Inoue@tpf.co.jp
From pgsql-hackers-owner+M3700@hub.org Wed Jun 21 22:17:59 2000
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From: "Hiroshi Inoue" <Inoue@tpf.co.jp>
To: "Tom Lane" <tgl@sss.pgh.pa.us>
Cc: "Bruce Momjian" <pgman@candle.pha.pa.us>,
"Peter Eisentraut" <peter_e@gmx.net>, "Jan Wieck" <JanWieck@Yahoo.com>,
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Subject: RE: [HACKERS] Big 7.1 open items
Date: Thu, 22 Jun 2000 10:15:01 +0900
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> -----Original Message-----
> From: Tom Lane [mailto:tgl@sss.pgh.pa.us]
>
> At the moment I can recall the following opinions:
>
> Pure OID filenames: Thomas, Tom, Marc, Peter E.
>
> OID+relname filenames: Bruce
>
Please add my opinion to the list.
Unique-id filename: Hiroshi
(Unqiue-id is irrelevant to OID/relname).
Regards.
Hiroshi Inoue
Inoue@tpf.co.jp
From pgsql-hackers-owner+M3701@hub.org Wed Jun 21 22:18:02 2000
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From: "Hiroshi Inoue" <Inoue@tpf.co.jp>
To: "Mikheev, Vadim" <vmikheev@SECTORBASE.COM>
Cc: "Bruce Momjian" <pgman@candle.pha.pa.us>,
"Peter Eisentraut" <peter_e@gmx.net>, "Jan Wieck" <JanWieck@Yahoo.com>,
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Subject: RE: [HACKERS] Big 7.1 open items
Date: Thu, 22 Jun 2000 10:27:26 +0900
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> -----Original Message-----
> From: Mikheev, Vadim [mailto:vmikheev@SECTORBASE.COM]
>
> > > Or - create tmp file and load with new content;
> > > log "intent to relink table file";
> > > relink table file; log "file is relinked".
> >
> > It seems to me that whole content of the table should be
> > logged before relinking or shrinking.
>
> Why not just fsync tmp files?
>
Probably I've misunderstood *relink*.
If *relink* different from *rename* ?
Regards.
Hiroshi Inoue
Inoue@tpf.co.jp
From vmikheev@SECTORBASE.COM Wed Jun 21 22:17:52 2000
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From: "Mikheev, Vadim" <vmikheev@SECTORBASE.COM>
To: "'Hiroshi Inoue'" <Inoue@tpf.co.jp>
Cc: Bruce Momjian <pgman@candle.pha.pa.us>,
Peter Eisentraut
<peter_e@gmx.net>, Jan Wieck <JanWieck@Yahoo.com>,
Bruce Momjian
<maillist@candle.pha.pa.us>,
PostgreSQL-development
<pgsql-hackers@postgreSQL.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>,
"'Tom Lane'" <tgl@sss.pgh.pa.us>,
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Subject: RE: [HACKERS] Big 7.1 open items
Date: Wed, 21 Jun 2000 18:30:23 -0700
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> > > > Or - create tmp file and load with new content;
> > > > log "intent to relink table file";
> > > > relink table file; log "file is relinked".
> > >
> > > It seems to me that whole content of the table should be
> > > logged before relinking or shrinking.
> >
> > Why not just fsync tmp files?
> >
>
> Probably I've misunderstood *relink*.
> If *relink* different from *rename* ?
I ment something like this - link(table file, tmp2 file); fsync(tmp2 file);
unlink(table file); link(tmp file, table file); fsync(table file);
unlink(tmp file). We can do additional logging (with log flush) of these
steps
if required, postpone on-recovery redo of operations till last relink log
record/
end of log/transaction abort etc etc etc.
Vadim
From Inoue@tpf.co.jp Wed Jun 21 23:22:36 2000
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From: "Hiroshi Inoue" <Inoue@tpf.co.jp>
To: "Mikheev, Vadim" <vmikheev@SECTORBASE.COM>
Cc: "Bruce Momjian" <pgman@candle.pha.pa.us>,
"Peter Eisentraut" <peter_e@gmx.net>, "Jan Wieck" <JanWieck@Yahoo.com>,
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Subject: RE: [HACKERS] Big 7.1 open items
Date: Thu, 22 Jun 2000 12:09:15 +0900
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> -----Original Message-----
> From: Mikheev, Vadim [mailto:vmikheev@SECTORBASE.COM]
>
> > > > > Or - create tmp file and load with new content;
> > > > > log "intent to relink table file";
> > > > > relink table file; log "file is relinked".
> > > >
> > > > It seems to me that whole content of the table should be
> > > > logged before relinking or shrinking.
> > >
> > > Why not just fsync tmp files?
> > >
> >
> > Probably I've misunderstood *relink*.
> > If *relink* different from *rename* ?
>
> I ment something like this - link(table file, tmp2 file);
> fsync(tmp2 file);
> unlink(table file); link(tmp file, table file); fsync(table file);
> unlink(tmp file).
I see,old file would be rolled back from tmp2 file on abort.
This would work on most platforms.
But cygwin port has a flaw that files could not be unlinked
if they are open. So *relink* may fail in some cases(including
rollback cases).
Regards.
Hiroshi Inoue
Inoue@tpf.co.jp
From tgl@sss.pgh.pa.us Wed Jun 21 23:22:38 2000
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To: "Mikheev, Vadim" <vmikheev@SECTORBASE.COM>
cc: Thomas Lockhart <lockhart@alumni.caltech.edu>,
Bruce Momjian <pgman@candle.pha.pa.us>,
Peter Eisentraut <peter_e@gmx.net>, Jan Wieck <JanWieck@Yahoo.com>,
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Subject: Re: [HACKERS] Big 7.1 open items
In-reply-to: <8F4C99C66D04D4118F580090272A7A23018C2B@SECTORBASE1>
References: <8F4C99C66D04D4118F580090272A7A23018C2B@SECTORBASE1>
Comments: In-reply-to "Mikheev, Vadim" <vmikheev@SECTORBASE.COM>
message dated "Wed, 21 Jun 2000 16:00:17 -0700"
Date: Wed, 21 Jun 2000 23:14:50 -0400
Message-ID: <7096.961643690@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
Status: RO
"Mikheev, Vadim" <vmikheev@SECTORBASE.COM> writes:
>> relation OID
>> relation version number
> I believe that we can avoid versions using WAL...
I don't think so. You're basically saying that
1. create file 'new'
2. delete file 'old'
3. rename 'new' to 'old'
is safe as long as you have a redo log to ensure that the rename
happens even if you crash between steps 2 and 3. But crash is not
the only hazard. What if step 3 just plain fails? Redo won't help.
I'm having a hard time inventing really plausible examples, but a
slightly implausible example is that someone chmod's the containing
directory -w between steps 2 and 3. (Maybe it's not so implausible
if you assume a crash after step 2 ... someone might have left the
directory nonwritable while restoring the system.)
If we use file version numbers, then the *only* thing needed to
make a valid transition between one set of files and another is
a commit of the update of pg_class that shows the new version number
in the rel's pg_class tuple. The worst that can happen to you in
a crash or other failure is that you are unable to get rid of the
set of files that you don't want anymore. That might waste disk
space but it doesn't leave the database corrupted.
> But what about LOCATIONs? I object using environment and think that
> locations must be stored in pg_control..?
I don't like environment variables for this either; it's just way too
easy to start the postmaster with wrong environment. It still seems
to me that relying on subdirectory symlinks is a good way to go.
pg_control is not so good --- if it gets corrupted, how do you recover?
symlinks can be recreated by hand if necessary, but...
regards, tom lane
From pgsql-hackers-owner+M3711@hub.org Thu Jun 22 01:01:06 2000
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To: "Hiroshi Inoue" <Inoue@tpf.co.jp>
cc: "Bruce Momjian" <pgman@candle.pha.pa.us>,
"Peter Eisentraut" <peter_e@gmx.net>, "Jan Wieck" <JanWieck@Yahoo.com>,
"PostgreSQL-development" <pgsql-hackers@postgresql.org>,
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Subject: Re: [HACKERS] Big 7.1 open items
In-reply-to: <000501bfdbe7$49fcdd20$2801007e@tpf.co.jp>
References: <000501bfdbe7$49fcdd20$2801007e@tpf.co.jp>
Comments: In-reply-to "Hiroshi Inoue" <Inoue@tpf.co.jp>
message dated "Thu, 22 Jun 2000 10:15:01 +0900"
Date: Wed, 21 Jun 2000 23:27:10 -0400
Message-ID: <7153.961644430@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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"Hiroshi Inoue" <Inoue@tpf.co.jp> writes:
> Please add my opinion to the list.
> Unique-id filename: Hiroshi
> (Unqiue-id is irrelevant to OID/relname).
"Unique ID" is more or less equivalent to "OID + version number",
right?
I was trying earlier to convince myself that a single unique-ID value
would be better than OID+version for the smgr interface, because it'd
certainly be easier to pass around. I failed to convince myself though,
and the thing that bothered me was this. Suppose you are trying to
recover a corrupted database manually, and the only information you have
about which table is which is a somewhat out-of-date listing of OIDs
versus table names. (Maybe it's out of date because you got it from
your last backup tape.) If the files are named OID+version you're not
going to have much trouble seeing which is which, even if some of the
versions are higher than what was on the tape. But if version-updated
tables are given entirely new unique IDs, you've got no hope at all of
telling which one corresponds to what you had in the listing. Maybe
you can tell by looking through the physical file contents, but
certainly this way is more fragile from the point of view of data
recovery.
regards, tom lane
From tgl@sss.pgh.pa.us Thu Jun 22 01:01:00 2000
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To: "Hiroshi Inoue" <Inoue@tpf.co.jp>
cc: "Bruce Momjian" <pgman@candle.pha.pa.us>,
"Peter Eisentraut" <peter_e@gmx.net>, "Jan Wieck" <JanWieck@Yahoo.com>,
"Bruce Momjian" <maillist@candle.pha.pa.us>,
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"Thomas Lockhart" <lockhart@alumni.caltech.edu>
Subject: Re: [HACKERS] Big 7.1 open items
In-reply-to: <000201bfdbd9$b1985580$2801007e@tpf.co.jp>
References: <000201bfdbd9$b1985580$2801007e@tpf.co.jp>
Comments: In-reply-to "Hiroshi Inoue" <Inoue@tpf.co.jp>
message dated "Thu, 22 Jun 2000 08:37:42 +0900"
Date: Thu, 22 Jun 2000 00:29:42 -0400
Message-ID: <7251.961648182@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
Status: RO
"Hiroshi Inoue" <Inoue@tpf.co.jp> writes:
> I strongly object to keep tablespace OID for smgr file reference token
> though we have to keep it for another purpose of cource. I've mentioned
> many times tablespace(where to store) info should be distinguished from
> *where it is stored* info.
Sure. But this proposal assumes that we're relying on symlinks to
carry the information about physical locations corresponding to
tablespace OIDs. The backend just needs to know enough to access a
relation file at a relative pathname like
tablespaceOID/relationOID
(ignoring version and segment numbers for now). Under the hood,
a symlink for tablespaceOID gets the work done.
Certainly this is not a perfect mechanism. But it is simple, it
is reliable, it is portable to most of the platforms we care about
(yeah, I know we have a Win port, but you wouldn't ever recommend
someone to run a *serious* database on it would you?), and in general
I think the bang-for-the-buck ratio is enormous. I do not want to
have to deal with explicit tablespace bookkeeping in the backend,
but that seems like what we'd have to do in order to improve on
symlinks.
regards, tom lane
From pgsql-hackers-owner+M3720@hub.org Thu Jun 22 02:01:02 2000
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Date: Wed, 21 Jun 2000 22:41:22 -0700
To: Chris Bitmead <chrisb@nimrod.itg.telstra.com.au>,
Bruce Momjian <pgman@candle.pha.pa.us>
From: Don Baccus <dhogaza@pacifier.com>
Subject: Re: [HACKERS] Big 7.1 open items
Cc: PostgreSQL-development <pgsql-hackers@postgreSQL.org>
In-Reply-To: <39518B7C.F76108FD@nimrod.itg.telecom.com.au>
References: <200006220229.WAA08130@candle.pha.pa.us>
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At 01:43 PM 6/22/00 +1000, Chris Bitmead wrote:
>I'm wondering if pg_dump should store the location of the tablespace. If
>your machine dies, you get a new machine to re-create the database, you
>may not want the tablespace in the same spot. And text-editing a
>gigabyte file would be extremely painful.
So you don't dump your create tablespace statements, recognizing that on
a new machine (due to upgrades or crashing) you might assign them to
different directories/mount points/whatever. That's the reason for
wanting to hide physical allocation in tablespaces ... the rest of
your datamodel doesn't need to know.
Or you do dump your tablespaces, and knowing the paths assigned
to various ones set up your new machine accordingly.
- Don Baccus, Portland OR <dhogaza@pacifier.com>
Nature photos, on-line guides, Pacific Northwest
Rare Bird Alert Service and other goodies at
http://donb.photo.net.
From dhogaza@pacifier.com Thu Jun 22 02:00:58 2000
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Date: Wed, 21 Jun 2000 22:51:49 -0700
To: Bruce Momjian <pgman@candle.pha.pa.us>,
Chris Bitmead <chrisb@nimrod.itg.telstra.com.au>
From: Don Baccus <dhogaza@pacifier.com>
Subject: Re: [HACKERS] Big 7.1 open items
Cc: PostgreSQL-development <pgsql-hackers@postgreSQL.org>
In-Reply-To: <200006220403.AAA15648@candle.pha.pa.us>
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At 12:03 AM 6/22/00 -0400, Bruce Momjian wrote:
>If the symlink create fails in CREATE TABLESPACE, it just creates an
>ordinary directory.
Silent surprises - the earmark of truly professional software ...
- Don Baccus, Portland OR <dhogaza@pacifier.com>
Nature photos, on-line guides, Pacific Northwest
Rare Bird Alert Service and other goodies at
http://donb.photo.net.
From Inoue@tpf.co.jp Thu Jun 22 02:01:00 2000
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From: "Hiroshi Inoue" <Inoue@tpf.co.jp>
To: "Tom Lane" <tgl@sss.pgh.pa.us>
Cc: "Bruce Momjian" <pgman@candle.pha.pa.us>,
"Peter Eisentraut" <peter_e@gmx.net>, "Jan Wieck" <JanWieck@Yahoo.com>,
"PostgreSQL-development" <pgsql-hackers@postgreSQL.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>,
"Thomas Lockhart" <lockhart@alumni.caltech.edu>
Subject: RE: [HACKERS] Big 7.1 open items
Date: Thu, 22 Jun 2000 14:56:07 +0900
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Status: RO
> -----Original Message-----
> From: Tom Lane [mailto:tgl@sss.pgh.pa.us]
>
> "Hiroshi Inoue" <Inoue@tpf.co.jp> writes:
> > I strongly object to keep tablespace OID for smgr file reference token
> > though we have to keep it for another purpose of cource. I've mentioned
> > many times tablespace(where to store) info should be distinguished from
> > *where it is stored* info.
>
> Sure. But this proposal assumes that we're relying on symlinks to
> carry the information about physical locations corresponding to
> tablespace OIDs. The backend just needs to know enough to access a
> relation file at a relative pathname like
> tablespaceOID/relationOID
> (ignoring version and segment numbers for now). Under the hood,
> a symlink for tablespaceOID gets the work done.
>
I think tablespaceOID is an easy substitution for the purpose.
I don't like to depend on poor directory tree structure in dbms
either..
> Certainly this is not a perfect mechanism. But it is simple, it
> is reliable, it is portable to most of the platforms we care about
> (yeah, I know we have a Win port, but you wouldn't ever recommend
> someone to run a *serious* database on it would you?), and in general
> I think the bang-for-the-buck ratio is enormous. I do not want to
> have to deal with explicit tablespace bookkeeping in the backend,
> but that seems like what we'd have to do in order to improve on
> symlinks.
>
I've already mentioned about it 10 times or so but unfortunately
I see no one on my side yet.
OK,I've given up the discussion about it. I don't want to waste
my time any more.
Regards.
Hiroshi Inoue
Inoue@tpf.co.jp
From tgl@sss.pgh.pa.us Thu Jun 22 03:31:04 2000
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To: Chris Bitmead <chrisb@nimrod.itg.telstra.com.au>
cc: Bruce Momjian <pgman@candle.pha.pa.us>,
PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: [HACKERS] Big 7.1 open items
In-reply-to: <39518B7C.F76108FD@nimrod.itg.telecom.com.au>
References: <200006220229.WAA08130@candle.pha.pa.us> <39518B7C.F76108FD@nimrod.itg.telecom.com.au>
Comments: In-reply-to Chris Bitmead <chrisb@nimrod.itg.telstra.com.au>
message dated "Thu, 22 Jun 2000 13:43:56 +1000"
Date: Thu, 22 Jun 2000 03:05:00 -0400
Message-ID: <7722.961657500@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
Status: RO
Chris Bitmead <chrisb@nimrod.itg.telstra.com.au> writes:
> I'm wondering if pg_dump should store the location of the tablespace. If
> your machine dies, you get a new machine to re-create the database, you
> may not want the tablespace in the same spot. And text-editing a
> gigabyte file would be extremely painful.
Might make sense to store the tablespace setup separately from the bulk
of the data, but certainly you want some way to dump that info in a
restorable form.
I've been thinking lately that the pg_dump shove-it-all-in-one-file
approach doesn't scale anyway. We ought to start thinking about ways
to make the standard dump method store schema separately from bulk
data, for example. That's offtopic for this thread but ought to be
on the TODO list someplace...
regards, tom lane
From pgsql-hackers-owner+M3727@hub.org Thu Jun 22 03:31:06 2000
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To: "Philip J. Warner" <pjw@rhyme.com.au>
cc: "Hiroshi Inoue" <Inoue@tpf.co.jp>,
"Bruce Momjian" <pgman@candle.pha.pa.us>,
"Peter Eisentraut" <peter_e@gmx.net>, "Jan Wieck" <JanWieck@Yahoo.com>,
"PostgreSQL-development" <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>,
"Thomas Lockhart" <lockhart@alumni.caltech.edu>
Subject: Re: [HACKERS] Big 7.1 open items
In-reply-to: <3.0.5.32.20000622163133.009b1600@mail.rhyme.com.au>
References: <000501bfdbe7$49fcdd20$2801007e@tpf.co.jp> <000501bfdbe7$49fcdd20$2801007e@tpf.co.jp> <3.0.5.32.20000622163133.009b1600@mail.rhyme.com.au>
Comments: In-reply-to "Philip J. Warner" <pjw@rhyme.com.au>
message dated "Thu, 22 Jun 2000 16:31:33 +1000"
Date: Thu, 22 Jun 2000 03:17:45 -0400
Message-ID: <7782.961658265@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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"Philip J. Warner" <pjw@rhyme.com.au> writes:
>> ... the thing that bothered me was this. Suppose you are trying to
>> recover a corrupted database manually, and the only information you have
>> about which table is which is a somewhat out-of-date listing of OIDs
>> versus table names.
> This worries me a little; in the Dec/RDB world it is a very long time since
> database backups were done by copying the files. There is a database
> backup/restore utility which runs while the database is on-line and makes
> sure a valid snapshot is taken. Backing up storage areas (table spapces)
> can be done separately by the same utility, and again, it records enough
> information to ensure integrity. Maybe the thing to do is write a pg_backup
> utility, which in a first pass could, presumably, be synonymous with pg_dump?
pg_dump already does the consistent-snapshot trick (it just has to run
inside a single transaction).
> Am I missing something here? Is there a problem with backing up using
> 'pg_dump | gzip'?
None, as long as your ambition extends no further than restoring your
data to where it was at your last pg_dump. I was thinking about the
all-too-common-in-the-real-world scenario where you're hoping to recover
some data more recent than your last backup from the fractured shards
of your database...
regards, tom lane
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From: Zeugswetter Andreas SB <zeugswettera@wien.spardat.at>
To: Chris Bitmead <chrisb@nimrod.itg.telstra.com.au>,
Bruce Momjian <pgman@candle.pha.pa.us>
Subject: Re: Big 7.1 open items
Date: Thu, 22 Jun 2000 09:49:07 +0200
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> > pg_dump would recreate a CREATE TABLESPACE command:
> >
> > printf("CREATE TABLESPACE %s USING %s", loc, symloc);
> >
> > where symloc would be SELECT symloc(loc) and return the value into a
> > variable that is used by pg_dump. The backend would do the lstat() and
> > return the value to the client.
>
> I'm wondering if pg_dump should store the location of the tablespace. If
> your machine dies, you get a new machine to re-create the database, you
> may not want the tablespace in the same spot. And text-editing a
> gigabyte file would be extremely painful.
Yes, that seems like a valid concern that should be kept in mind.
It should also be possible to restore a pg instance to a different location
on the same machine.
Maybe this could be done by adding a utility that dumps all tablespace
info which could then be altered to desire.
I still opt for instance-wide tablespaces. People wanting separation can easily
create different tablespaces for each database, but those that only want to
separate data and index need only create two tablespaces. A typical installation would
have 1 to 4 tablespaces (systemtbs, datatbs, indextbs, toasttbs | lobdbs )
I would also switch the directory structure between dbname and extent subdir,
because that allows less symlinks/filesystems, and thus less admin.
thus you would have:
tablespace1/extent1/dbname1
tablespace1/extent2/dbname1
tablespace1/extent1/dbname2
Andreas
From pjw@rhyme.com.au Thu Jun 22 04:01:05 2000
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To: Tom Lane <tgl@sss.pgh.pa.us>
From: "Philip J. Warner" <pjw@rhyme.com.au>
Subject: Re: [HACKERS] Big 7.1 open items
Cc: "Hiroshi Inoue" <Inoue@tpf.co.jp>,
"Bruce Momjian" <pgman@candle.pha.pa.us>,
"Peter Eisentraut" <peter_e@gmx.net>, "Jan Wieck" <JanWieck@Yahoo.com>,
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At 03:17 22/06/00 -0400, Tom Lane wrote:
>
>> This worries me a little; in the Dec/RDB world it is a very long time since
>> database backups were done by copying the files. There is a database
>> backup/restore utility which runs while the database is on-line and makes
>> sure a valid snapshot is taken. Backing up storage areas (table spapces)
>> can be done separately by the same utility, and again, it records enough
>> information to ensure integrity. Maybe the thing to do is write a pg_backup
>> utility, which in a first pass could, presumably, be synonymous with
pg_dump?
>
>pg_dump already does the consistent-snapshot trick (it just has to run
>inside a single transaction).
>
>> Am I missing something here? Is there a problem with backing up using
>> 'pg_dump | gzip'?
>
>None, as long as your ambition extends no further than restoring your
>data to where it was at your last pg_dump. I was thinking about the
>all-too-common-in-the-real-world scenario where you're hoping to recover
>some data more recent than your last backup from the fractured shards
>of your database...
>
pg_dump is a good basis for any pg_backup utility; perhaps as you indicated
elsewhere, more carefull formatting of the dump files would make
table-based restoration possible. In another response, I also suggested
allowing overrides of placement information in a restore operation- the
simplest approach would be an 'ignore-storage-parameters' flag. Does this
sound reasonable? If so, then discussion of file-id based on OID needs not
be too concerned about how db restoration is done.
----------------------------------------------------------------
Philip Warner | __---_____
Albatross Consulting Pty. Ltd. |----/ - \
(A.C.N. 008 659 498) | /(@) ______---_
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From pgsql-hackers-owner+M3730@hub.org Thu Jun 22 05:31:00 2000
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From: "Hiroshi Inoue" <Inoue@tpf.co.jp>
To: "Peter Eisentraut" <peter_e@gmx.net>
Cc: "Tom Lane" <tgl@sss.pgh.pa.us>, "Bruce Momjian" <pgman@candle.pha.pa.us>,
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Subject: RE: [HACKERS] Big 7.1 open items
Date: Thu, 22 Jun 2000 18:07:18 +0900
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> -----Original Message-----
> From: Peter Eisentraut [mailto:e99re41@DoCS.UU.SE]
>
> > My opinion
> > 3) database and tablespace are relatively irrelevant.
> > I assume PostgreSQL's database would correspond
> > to the concept of SCHEMA.
>
> A database corresponds to a catalog and a schema corresponds to nothing
> yet.
>
Oh I see your point. However I've thought that current PostgreSQL's
database is an imcomplete SCHEMA and still feel so in reality.
Catalog per database has been nothing but needless for me from
the first.
Regards.
Hiroshi Inoue
Inoue@tpf.co.jp
From Inoue@tpf.co.jp Thu Jun 22 07:31:01 2000
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From: "Hiroshi Inoue" <Inoue@tpf.co.jp>
To: "Tom Lane" <tgl@sss.pgh.pa.us>
Cc: "Bruce Momjian" <pgman@candle.pha.pa.us>,
"Peter Eisentraut" <peter_e@gmx.net>, "Jan Wieck" <JanWieck@Yahoo.com>,
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Subject: RE: [HACKERS] Big 7.1 open items
Date: Thu, 22 Jun 2000 20:09:07 +0900
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> -----Original Message-----
> From: Tom Lane [mailto:tgl@sss.pgh.pa.us]
>
> "Hiroshi Inoue" <Inoue@tpf.co.jp> writes:
> > Please add my opinion to the list.
> > Unique-id filename: Hiroshi
> > (Unqiue-id is irrelevant to OID/relname).
>
> "Unique ID" is more or less equivalent to "OID + version number",
> right?
>
Hmm,no one seems to be on my side at this point also.
OK,I change my mind as follows.
OID except cygwin,unique-id on cygwin
Regards.
Hiroshi Inoue
Inoue@tpf.co.jp
From tgl@sss.pgh.pa.us Thu Jun 22 11:31:06 2000
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To: "Hiroshi Inoue" <Inoue@tpf.co.jp>
cc: "Bruce Momjian" <pgman@candle.pha.pa.us>,
"Peter Eisentraut" <peter_e@gmx.net>, "Jan Wieck" <JanWieck@Yahoo.com>,
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Subject: Re: [HACKERS] Big 7.1 open items
In-reply-to: <000d01bfdc3a$48fb35e0$2801007e@tpf.co.jp>
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Comments: In-reply-to "Hiroshi Inoue" <Inoue@tpf.co.jp>
message dated "Thu, 22 Jun 2000 20:09:07 +0900"
Date: Thu, 22 Jun 2000 11:27:30 -0400
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From: Tom Lane <tgl@sss.pgh.pa.us>
Status: RO
"Hiroshi Inoue" <Inoue@tpf.co.jp> writes:
> OK,I change my mind as follows.
> OID except cygwin,unique-id on cygwin
We don't really want to do that, do we? That's a huge difference in
behavior to have in just one port --- especially a port that none of
the primary developers use (AFAIK anyway). The cygwin port's normal
state of existence will be "broken", surely, if we go that way.
Besides which, OID alone doesn't give us a possibility of file
versioning, and as I commented to Vadim I think we will want that,
WAL or no WAL. So it seems to me the two viable choices are
unique-id or OID+version-number. Either way, the file-naming behavior
should be the same across all platforms.
regards, tom lane
From vmikheev@SECTORBASE.COM Thu Jun 22 14:31:00 2000
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From: "Mikheev, Vadim" <vmikheev@SECTORBASE.COM>
To: "'Tom Lane'" <tgl@sss.pgh.pa.us>
Cc: Thomas Lockhart <lockhart@alumni.caltech.edu>,
Bruce Momjian
<pgman@candle.pha.pa.us>,
Peter Eisentraut <peter_e@gmx.net>, Jan Wieck
<JanWieck@Yahoo.com>,
Hiroshi Inoue <Inoue@tpf.co.jp>,
PostgreSQL-development <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: RE: [HACKERS] Big 7.1 open items
Date: Thu, 22 Jun 2000 11:09:47 -0700
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> > I believe that we can avoid versions using WAL...
>
> I don't think so. You're basically saying that
> 1. create file 'new'
> 2. delete file 'old'
> 3. rename 'new' to 'old'
> is safe as long as you have a redo log to ensure that the rename
> happens even if you crash between steps 2 and 3. But crash is not
> the only hazard. What if step 3 just plain fails? Redo won't help.
Ok, ok. Let's use *unique* file name for each table version.
But after thinking, seems that I agreed with Hiroshi about using
*some unique id* for file names instead of oid+version: we could use
just DB' OID + this unique ID in log records to find table file - just
8 bytes.
So, add me to Hiroshi' camp... if Hiroshi is ready to implement new file
naming -:)
> > But what about LOCATIONs? I object using environment and think that
> > locations must be stored in pg_control..?
>
> I don't like environment variables for this either; it's just way too
> easy to start the postmaster with wrong environment. It still seems
> to me that relying on subdirectory symlinks is a good way to go.
I always thought so.
> pg_control is not so good --- if it gets corrupted, how do
> you recover?
Impossible to recover anyway - pg_control keeps last checkpoint pointer,
required for recovery. That's why Oracle recommends (requires?) at least
two copies of control file (and log too).
But what if log gets corrupted? Or file system (lost symlinks etc)?
One will have to use backup...
Vadim
From peter@localhost.its.uu.se Thu Jun 22 18:37:35 2000
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From: Peter Eisentraut <peter_e@gmx.net>
To: Tom Lane <tgl@sss.pgh.pa.us>
cc: Hiroshi Inoue <Inoue@tpf.co.jp>, Bruce Momjian <pgman@candle.pha.pa.us>,
Jan Wieck <JanWieck@Yahoo.com>,
PostgreSQL-development <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: Re: [HACKERS] Big 7.1 open items
In-Reply-To: <8803.961687343@sss.pgh.pa.us>
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Status: RO
Tom Lane writes:
> In my mind the point of the "database" concept is to provide a domain
> within which custom datatypes and functions are available.
Quoth SQL99:
"A user-defined type is a schema object"
"An SQL-invoked routine is an element of an SQL-schema"
I have yet to see anything in SQL that's a per-catalog object. Some things
are global, like users, but everything else is per-schema.
The way I see it is that schemas are required to be a logical hierarchy,
whereas implementations may see catalogs as a physical division (as indeed
this implementation does).
> So I think we will still want "database" = "span of applicability of
> system catalogs"
Yes, because the system catalogs would live in a schema of their own.
--
Peter Eisentraut Sernanders v<>g 10:115
peter_e@gmx.net 75262 Uppsala
http://yi.org/peter-e/ Sweden
From ZeugswetterA@wien.spardat.at Mon Jun 26 04:10:01 2000
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From: Zeugswetter Andreas SB <ZeugswetterA@wien.spardat.at>
To: "'Tom Lane'" <tgl@sss.pgh.pa.us>, Hiroshi Inoue <Inoue@tpf.co.jp>
Cc: Bruce Momjian <pgman@candle.pha.pa.us>,
Peter Eisentraut
<peter_e@gmx.net>, Jan Wieck <JanWieck@Yahoo.com>,
PostgreSQL-development <pgsql-hackers@postgresql.org>,
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Subject: [HACKERS] File versioning (was: Big 7.1 open items)
Date: Mon, 26 Jun 2000 10:09:13 +0200
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> Besides which, OID alone doesn't give us a possibility of file
> versioning, and as I commented to Vadim I think we will want that,
> WAL or no WAL. So it seems to me the two viable choices are
> unique-id or OID+version-number. Either way, the file-naming behavior
> should be the same across all platforms.
I do not think the only problem of a failing rename of "temp" to "new"
on startup rollforward is issue enough to justify the additional complexity
a version implys.
Why not simply abort startup of postmaster in such an event and let the
dba fix it. There can be no data loss.
If e.g. the permissions of the directory are insufficient we will want to
abort
startup anyway, no?
Andreas
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From: Zeugswetter Andreas SB <ZeugswetterA@wien.spardat.at>
To: "'Hiroshi Inoue'" <Inoue@tpf.co.jp>, Peter Eisentraut <peter_e@gmx.net>,
Tom Lane <tgl@sss.pgh.pa.us>
Cc: Bruce Momjian <pgman@candle.pha.pa.us>, Jan Wieck <JanWieck@Yahoo.com>,
PostgreSQL-development <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: AW: [HACKERS] Big 7.1 open items
Date: Mon, 26 Jun 2000 11:31:06 +0200
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> > > In my mind the point of the "database" concept is to
> provide a domain
> > > within which custom datatypes and functions are available.
> >
>
> AFAIK few users understand it and many users have wondered
> why we couldn't issue cross "database" queries.
Imho the same issue is access to tables on another machine.
If we "fix" that, access to another db on the same instance is just
a variant of the above.
>
> > Quoth SQL99:
> >
> > "A user-defined type is a schema object"
> >
> > "An SQL-invoked routine is an element of an SQL-schema"
> >
> > I have yet to see anything in SQL that's a per-catalog
> object. Some things
> > are global, like users, but everything else is per-schema.
Yes.
> So why is system catalog needed per "database" ?
I like to use different databases on a development machine,
because it makes testing easier. The only thing that
needs to be changed is the connect statement. All other statements
including schema qualified tablenames stay exactly the same for
each developer even though each has his own database,
and his own version of functions.
I have yet to see an installation that does'nt have at least one program
that needs access to more than one schema.
On production machines we (using Informix) use different databases
for different products, because it reduces the possibility of accessing
the wrong tables, since the syntax for accessing tables in other db's
is different (dbname[@instancename]:"owner".tabname in Informix)
The schema does not help us, since most of our programs access
tables from more than one schema.
And again someone wanting Oracle'ish behavior will only create one
database per instance.
Andreas
From pgsql-hackers-owner+M4088@hub.org Mon Jul 3 01:57:49 2000
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From: "Hiroshi Inoue" <Inoue@seiren.co.jp>
To: "Zeugswetter Andreas SB" <ZeugswetterA@wien.spardat.at>,
"Peter Eisentraut" <peter_e@gmx.net>, "Tom Lane" <tgl@sss.pgh.pa.us>
Cc: "Bruce Momjian" <pgman@candle.pha.pa.us>, "Jan Wieck" <JanWieck@Yahoo.com>,
"PostgreSQL-development" <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: RE: [HACKERS] Big 7.1 open items
Date: Mon, 26 Jun 2000 19:08:26 +0900
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> -----Original Message-----
> From: Zeugswetter Andreas SB
>
> > > > In my mind the point of the "database" concept is to
> > provide a domain
> > > > within which custom datatypes and functions are available.
> > >
> >
> > AFAIK few users understand it and many users have wondered
> > why we couldn't issue cross "database" queries.
>
> Imho the same issue is access to tables on another machine.
> If we "fix" that, access to another db on the same instance is just
> a variant of the above.
>
What is a difference between SCHAMA and your "database" ?
I myself am confused about them.
Regards.
Hiroshi Inoue
Inoue@tpf.co.jp
From ZeugswetterA@wien.spardat.at Mon Jun 26 06:50:26 2000
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Message-ID: <219F68D65015D011A8E000006F8590C605BA5991@sdexcsrv1.f000.d0188.sd.spardat.at>
From: Zeugswetter Andreas SB <ZeugswetterA@wien.spardat.at>
To: "'Hiroshi Inoue'" <Inoue@seiren.co.jp>,
Peter Eisentraut
<peter_e@gmx.net>, Tom Lane <tgl@sss.pgh.pa.us>
Cc: Bruce Momjian <pgman@candle.pha.pa.us>, Jan Wieck <JanWieck@Yahoo.com>,
PostgreSQL-development <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: AW: [HACKERS] Big 7.1 open items
Date: Mon, 26 Jun 2000 12:50:10 +0200
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Hiroshi Inoue [mailto:Inoue@seiren.co.jp] wrote:
> > > > > In my mind the point of the "database" concept is to
> > > provide a domain
> > > > > within which custom datatypes and functions are available.
> > > >
> > >
> > > AFAIK few users understand it and many users have wondered
> > > why we couldn't issue cross "database" queries.
> >
> > Imho the same issue is access to tables on another machine.
> > If we "fix" that, access to another db on the same instance is just
> > a variant of the above.
> >
>
> What is a difference between SCHAMA and your "database" ?
> I myself am confused about them.
Think of it as a hierarchy:
instance -> database -> schema -> object
- "instance" corresponds to one postmaster
- "database" as in current implementation
- "schema" name corresponds to the owner of the object,
only that a corresponding db or os user does not need to exist in
some of the implementations I know.
- "object" is one of table, index, function ...
The database is what you connect to in your connect statement,
you then see all schemas inside this database only. Access to another
database would need an explicitly created synonym or different syntax.
The default "schema" name is usually the logged in user name
(although I don't like this approach, I like Informix's approach where
the schema need not be specified if tabname is unique (and tabname
is unique per db unless you specify database mode ansi)).
All other schemas have to be explicitly named ("schemaname".tabname).
Oracle has exactly this layout, only you are restricted to one database
per instance.
(They even have a "create database .." statement, although it is somehow
analogous to our initdb).
Andreas
From ZeugswetterA@wien.spardat.at Mon Jun 26 07:51:14 2000
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Message-ID: <219F68D65015D011A8E000006F8590C605BA5993@sdexcsrv1.f000.d0188.sd.spardat.at>
From: Zeugswetter Andreas SB <ZeugswetterA@wien.spardat.at>
To: "'Mikheev, Vadim'" <vmikheev@SECTORBASE.COM>,
"'Tom Lane'"
<tgl@sss.pgh.pa.us>
Cc: Thomas Lockhart <lockhart@alumni.caltech.edu>,
Bruce Momjian
<pgman@candle.pha.pa.us>,
Peter Eisentraut <peter_e@gmx.net>, Jan Wieck
<JanWieck@Yahoo.com>,
Hiroshi Inoue <Inoue@tpf.co.jp>,
PostgreSQL-development <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: AW: [HACKERS] Big 7.1 open items
Date: Mon, 26 Jun 2000 13:50:55 +0200
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Vadim wrote:
> Impossible to recover anyway - pg_control keeps last
> checkpoint pointer, required for recovery.
Why not put this info in the tx log itself.
> That's why Oracle recommends (requires?) at least
> two copies of control file ....
This is one of the most stupid design issues Oracle has.
I suggest you look at the tx log design of Informix.
(No Informix dba fears to pull the power cord on his servers,
ask the same of an Oracle dba, they even fear
"shutdown immediate" on a heavily used db)
Andreas
From ZeugswetterA@wien.spardat.at Mon Jun 26 08:02:07 2000
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Message-ID: <219F68D65015D011A8E000006F8590C605BA5994@sdexcsrv1.f000.d0188.sd.spardat.at>
From: Zeugswetter Andreas SB <ZeugswetterA@wien.spardat.at>
To: Zeugswetter Andreas SB <ZeugswetterA@wien.spardat.at>,
"'Mikheev, Vadim'" <vmikheev@SECTORBASE.COM>,
"'Tom Lane'"
<tgl@sss.pgh.pa.us>
Cc: Thomas Lockhart <lockhart@alumni.caltech.edu>,
Bruce Momjian
<pgman@candle.pha.pa.us>,
Peter Eisentraut <peter_e@gmx.net>, Jan Wieck
<JanWieck@Yahoo.com>,
Hiroshi Inoue <Inoue@tpf.co.jp>,
PostgreSQL-development <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: AW: [HACKERS] Big 7.1 open items
Date: Mon, 26 Jun 2000 14:01:15 +0200
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I wrote:
> Vadim wrote:
> > Impossible to recover anyway - pg_control keeps last
> > checkpoint pointer, required for recovery.
>
> Why not put this info in the tx log itself.
>
> > That's why Oracle recommends (requires?) at least
> > two copies of control file ....
>
> This is one of the most stupid design issues Oracle has.
The problem is, that if you want to switch to a no fsync environment,
(here I also mean the tx log)
but the possibility of losing a write is still there, you cannot sync
writes to two or more different files. Only one file, the tx log itself is
allowed
to carry lastminute information.
Thus you need to txlog changes to pg_control also.
Andreas
From tgl@sss.pgh.pa.us Mon Jun 26 10:42:08 2000
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To: Zeugswetter Andreas SB <ZeugswetterA@Wien.Spardat.at>
cc: Hiroshi Inoue <Inoue@tpf.co.jp>, Bruce Momjian <pgman@candle.pha.pa.us>,
Peter Eisentraut <peter_e@gmx.net>, Jan Wieck <JanWieck@yahoo.com>,
PostgreSQL-development <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>,
Thomas Lockhart <lockhart@alumni.caltech.edu>
Subject: Re: [HACKERS] File versioning (was: Big 7.1 open items)
In-reply-to: <219F68D65015D011A8E000006F8590C605BA598B@sdexcsrv1.f000.d0188.sd.spardat.at>
References: <219F68D65015D011A8E000006F8590C605BA598B@sdexcsrv1.f000.d0188.sd.spardat.at>
Comments: In-reply-to Zeugswetter Andreas SB <ZeugswetterA@Wien.Spardat.at>
message dated "Mon, 26 Jun 2000 10:09:13 +0200"
Date: Mon, 26 Jun 2000 10:42:31 -0400
Message-ID: <17015.962030551@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
Status: RO
Zeugswetter Andreas SB <ZeugswetterA@Wien.Spardat.at> writes:
> I do not think the only problem of a failing rename of "temp" to "new"
> on startup rollforward is issue enough to justify the additional complexity
> a version implys.
If that were the only reason for it then I wouldn't feel it was so
essential. However, it will also let us fix CLUSTER, vacuuming of
indexes, ALTER TABLE DROP COLUMN with physical removal of the column,
etc etc. Making the world safe for rollbackable RENAME/DROP/TRUNCATE
TABLE is just one of the benefits.
Versioning also eliminates a whole host of problems at the bufmgr/smgr
level that are caused by having to cope with relation files getting
renamed out from under you. We have painfully eliminated some of these
problems over the past couple of years by ad-hoc, ugly techniques like
flushing the buffer cache when doing a rename. But who's to say there
are not more such bugs left?
In short, I think versioning is far *less* complex, not to mention more
reliable, than the kluges we need to use to work around the lack of it.
regards, tom lane
From pgsql-hackers-owner+M3879@hub.org Mon Jun 26 18:30:55 2000
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From: "Mikheev, Vadim" <vmikheev@SECTORBASE.COM>
To: "'Tom Lane'" <tgl@sss.pgh.pa.us>
Cc: "'Hiroshi Inoue'" <Inoue@tpf.co.jp>,
Thomas Lockhart
<lockhart@alumni.caltech.edu>,
Bruce Momjian <pgman@candle.pha.pa.us>,
Peter Eisentraut <peter_e@gmx.net>, Jan Wieck <JanWieck@Yahoo.com>,
PostgreSQL-development <pgsql-hackers@postgresql.org>,
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Subject: RE: [HACKERS] Big 7.1 open items
Date: Mon, 26 Jun 2000 15:15:39 -0700
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> > Do we need *both* database & tablespace to find table file ?!
> > Imho, database shouldn't be used...
>
> That'd work fine for me, but I think Bruce was arguing for paths that
> included the database name. We'd end up with paths that go something
> like
> ..../data/tablespaces/TABLESPACEOID/RELATIONOID
> (plus some kind of decoration for segment and version), so you'd have
> a hard time telling which files in a tablespace belong to which
> database. Doesn't bother me a whole lot, personally --- if one wants
We could create /data/databases/DATABASEOID/ and create soft-links to
table-files. This way different tables of the same database could be in
different tablespaces. /data/database path would be used in production
and /data/tablespace path would be used in recovery.
Vadim
From vmikheev@SECTORBASE.COM Mon Jun 26 18:21:53 2000
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From: "Mikheev, Vadim" <vmikheev@SECTORBASE.COM>
To: "'Tom Lane'" <tgl@sss.pgh.pa.us>
Cc: "'Hiroshi Inoue'" <Inoue@tpf.co.jp>,
Thomas Lockhart
<lockhart@alumni.caltech.edu>,
Bruce Momjian <pgman@candle.pha.pa.us>,
Peter Eisentraut <peter_e@gmx.net>, Jan Wieck <JanWieck@Yahoo.com>,
PostgreSQL-development <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: RE: [HACKERS] Big 7.1 open items
Date: Mon, 26 Jun 2000 15:15:39 -0700
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> > Do we need *both* database & tablespace to find table file ?!
> > Imho, database shouldn't be used...
>
> That'd work fine for me, but I think Bruce was arguing for paths that
> included the database name. We'd end up with paths that go something
> like
> ..../data/tablespaces/TABLESPACEOID/RELATIONOID
> (plus some kind of decoration for segment and version), so you'd have
> a hard time telling which files in a tablespace belong to which
> database. Doesn't bother me a whole lot, personally --- if one wants
We could create /data/databases/DATABASEOID/ and create soft-links to
table-files. This way different tables of the same database could be in
different tablespaces. /data/database path would be used in production
and /data/tablespace path would be used in recovery.
Vadim
From tgl@sss.pgh.pa.us Mon Jun 26 18:47:54 2000
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To: "Mikheev, Vadim" <vmikheev@SECTORBASE.COM>
cc: "'Hiroshi Inoue'" <Inoue@tpf.co.jp>,
Thomas Lockhart <lockhart@alumni.caltech.edu>,
Bruce Momjian <pgman@candle.pha.pa.us>,
Peter Eisentraut <peter_e@gmx.net>, Jan Wieck <JanWieck@Yahoo.com>,
PostgreSQL-development <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: Re: [HACKERS] Big 7.1 open items
In-reply-to: <8F4C99C66D04D4118F580090272A7A23018C36@SECTORBASE1>
References: <8F4C99C66D04D4118F580090272A7A23018C36@SECTORBASE1>
Comments: In-reply-to "Mikheev, Vadim" <vmikheev@SECTORBASE.COM>
message dated "Mon, 26 Jun 2000 15:15:39 -0700"
Date: Mon, 26 Jun 2000 18:48:22 -0400
Message-ID: <19576.962059702@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
Status: RO
"Mikheev, Vadim" <vmikheev@SECTORBASE.COM> writes:
> We could create /data/databases/DATABASEOID/ and create soft-links to
> table-files. This way different tables of the same database could be in
> different tablespaces. /data/database path would be used in production
> and /data/tablespace path would be used in recovery.
Why would you want to do it that way? Having a different access path
for recovery than for normal operation strikes me as just asking for
trouble ;-)
The symlinks wouldn't do any good for what Bruce had in mind anyway
(IIRC, he wanted to get useful per-database numbers from "du").
regards, tom lane
From pgsql-hackers-owner+M3888@hub.org Mon Jun 26 23:37:52 2000
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Message-ID: <8F4C99C66D04D4118F580090272A7A23018C38@SECTORBASE1>
From: "Mikheev, Vadim" <vmikheev@SECTORBASE.COM>
To: "'Tom Lane'" <tgl@sss.pgh.pa.us>
Cc: "'Hiroshi Inoue'" <Inoue@tpf.co.jp>,
Thomas Lockhart
<lockhart@alumni.caltech.edu>,
Bruce Momjian <pgman@candle.pha.pa.us>,
Peter Eisentraut <peter_e@gmx.net>, Jan Wieck <JanWieck@Yahoo.com>,
PostgreSQL-development <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: RE: [HACKERS] Big 7.1 open items
Date: Mon, 26 Jun 2000 18:42:10 -0700
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> > We could create /data/databases/DATABASEOID/ and create
> > soft-links to table-files. This way different tables of
> > the same database could be in different tablespaces.
> > /data/database path would be used in production
> > and /data/tablespace path would be used in recovery.
>
> Why would you want to do it that way? Having a different access path
> for recovery than for normal operation strikes me as just asking for
> trouble ;-)
I just think that *databases* (schemas) must be used for *logical* groupping
of tables, not for *physical* one. "Where to store table" is tablespace'
related kind of things!
> The symlinks wouldn't do any good for what Bruce had in mind anyway
> (IIRC, he wanted to get useful per-database numbers from "du").
Imho, ability to put different tables/indices (of the same database)
to different tablespaces (disks) is much more useful then ability to
use du/ls for administration purposes -:)
Also, I think that we *must* go away from OS' driven disk space
allocation anyway. Currently, the way we extend table files breaks WAL
rule (nothing must go to disk untill logged). + we have to move tuples
from end of file to top to shrink relation - not perfect way to reuse
empty space. +... +... +...
Vadim
From Inoue@tpf.co.jp Tue Jun 27 00:05:13 2000
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From: Hiroshi Inoue <Inoue@tpf.co.jp>
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CC: "Mikheev, Vadim" <vmikheev@SECTORBASE.COM>,
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Bruce Momjian <pgman@candle.pha.pa.us>,
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Subject: Re: [HACKERS] Big 7.1 open items
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Tom Lane wrote:
>
> The symlinks wouldn't do any good for what Bruce had in mind anyway
> (IIRC, he wanted to get useful per-database numbers from "du").
Our database design seems to be in the opposite direction
if it is restricted for the convenience of command calls.
Regards.
Hiroshi Inoue
Inoue@tpf.co.jp
From pgsql-hackers-owner+M3892@hub.org Tue Jun 27 00:14:24 2000
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CC: "Mikheev, Vadim" <vmikheev@SECTORBASE.COM>,
Thomas Lockhart <lockhart@alumni.caltech.edu>,
Bruce Momjian <pgman@candle.pha.pa.us>,
Peter Eisentraut <peter_e@gmx.net>, Jan Wieck <JanWieck@Yahoo.com>,
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Subject: Re: [HACKERS] Big 7.1 open items
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Tom Lane wrote:
>
> The symlinks wouldn't do any good for what Bruce had in mind anyway
> (IIRC, he wanted to get useful per-database numbers from "du").
Our database design seems to be in the opposite direction
if it is restricted for the convenience of command calls.
Regards.
Hiroshi Inoue
Inoue@tpf.co.jp
From pgsql-hackers-owner+M3905@hub.org Tue Jun 27 10:07:49 2000
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From: Zeugswetter Andreas SB <ZeugswetterA@wien.spardat.at>
To: "'Tom Lane'" <tgl@sss.pgh.pa.us>,
"Mikheev, Vadim"
<vmikheev@SECTORBASE.COM>
Cc: "'Hiroshi Inoue'" <Inoue@tpf.co.jp>,
Thomas Lockhart
<lockhart@alumni.caltech.edu>,
Bruce Momjian <pgman@candle.pha.pa.us>,
Peter Eisentraut <peter_e@gmx.net>, Jan Wieck <JanWieck@Yahoo.com>,
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"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: AW: [HACKERS] Big 7.1 open items
Date: Tue, 27 Jun 2000 15:27:03 +0200
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> That'd work fine for me, but I think Bruce was arguing for paths that
> included the database name. We'd end up with paths that go something
> like
> ..../data/tablespaces/TABLESPACEOID/RELATIONOID
> (plus some kind of decoration for segment and version), so you'd have
> a hard time telling which files in a tablespace belong to which
> database.
Well ,as long as we have the file per object layout it probably makes sense
to
have "speaking paths", But I see no real problem with:
..../data/tablespacename/dbname/RELATIONOID[.dat|.idx]
RELATIONOID standing for whatever the consensus will be.
I do not really see an argument for using a tablespaceoid instead of
it's [maybe mangled] name.
Andreas
From pgsql-hackers-owner+M3912@hub.org Tue Jun 27 10:28:39 2000
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To: Zeugswetter Andreas SB <ZeugswetterA@wien.spardat.at>
cc: "Mikheev, Vadim" <vmikheev@SECTORBASE.COM>,
"'Hiroshi Inoue'" <Inoue@tpf.co.jp>,
Thomas Lockhart <lockhart@alumni.caltech.edu>,
Bruce Momjian <pgman@candle.pha.pa.us>,
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"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: Re: AW: [HACKERS] Big 7.1 open items
In-reply-to: <219F68D65015D011A8E000006F8590C605BA5999@sdexcsrv1.f000.d0188.sd.spardat.at>
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Comments: In-reply-to Zeugswetter Andreas SB <ZeugswetterA@wien.spardat.at>
message dated "Tue, 27 Jun 2000 15:27:03 +0200"
Date: Tue, 27 Jun 2000 10:23:48 -0400
Message-ID: <9572.962115828@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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Zeugswetter Andreas SB <ZeugswetterA@wien.spardat.at> writes:
> I do not really see an argument for using a tablespaceoid instead of
> it's [maybe mangled] name.
Eliminating filesystem-based restrictions on names, for one.
For example we'd not have to forbid slashes and (probably) backquotes
in tablespace names if we did this, and we'd not have to worry about
filesystem-induced limits on name lengths. Renaming a tablespace
would also be trivial instead of nigh impossible.
It might be that using tablespace names as directory names is worth
enough from the admin point of view to make the above restrictions
acceptable. But it's a tradeoff, and not one with an obvious choice
IMHO.
regards, tom lane
From vmikheev@SECTORBASE.COM Tue Jun 27 14:01:08 2000
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From: "Mikheev, Vadim" <vmikheev@SECTORBASE.COM>
To: "'Bruce Momjian'" <pgman@candle.pha.pa.us>,
Hiroshi Inoue
<Inoue@tpf.co.jp>
Cc: Tom Lane <tgl@sss.pgh.pa.us>,
Thomas Lockhart
<lockhart@alumni.caltech.edu>,
Peter Eisentraut <peter_e@gmx.net>, Jan Wieck <JanWieck@Yahoo.com>,
PostgreSQL-development
<pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: RE: [HACKERS] Big 7.1 open items
Date: Tue, 27 Jun 2000 10:54:55 -0700
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> > > The symlinks wouldn't do any good for what Bruce had in
> > > mind anyway (IIRC, he wanted to get useful per-database
> > > numbers from "du").
> >
> > Our database design seems to be in the opposite direction
> > if it is restricted for the convenience of command calls.
>
> Well, I don't see any reason not to use tablespace/database
> rather than just tablespace. Seems having fewer files in each directory
Once again - ability to use different tablespaces (disks) for tables/indices
in the same schema. Schemas must not dictate where to store objects <-
bad design.
> will be a little faster, and if we can make administration easier,
> why not?
Because you'll not be able use du/ls once we'll implement new smgr anyway.
And, btw, - for what are we going implement tablespaces? Just to have
fewer files in each dir ?!
Vadim
From pgsql-hackers-owner+M3925@hub.org Tue Jun 27 14:03:35 2000
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Date: Tue, 27 Jun 2000 20:07:34 +0200 (CEST)
From: Peter Eisentraut <peter_e@gmx.net>
To: "Mikheev, Vadim" <vmikheev@SECTORBASE.COM>
cc: "'Hiroshi Inoue'" <Inoue@tpf.co.jp>, "'Tom Lane'" <tgl@sss.pgh.pa.us>,
Thomas Lockhart <lockhart@alumni.caltech.edu>,
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Subject: RE: [HACKERS] Big 7.1 open items
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Mikheev, Vadim writes:
> Do we need *both* database & tablespace to find table file ?!
> Imho, database shouldn't be used...
Then the system tables from different databases would collide.
--
Peter Eisentraut Sernanders v<>g 10:115
peter_e@gmx.net 75262 Uppsala
http://yi.org/peter-e/ Sweden
From vmikheev@SECTORBASE.COM Tue Jun 27 15:28:25 2000
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From: "Mikheev, Vadim" <vmikheev@SECTORBASE.COM>
To: "'Bruce Momjian'" <pgman@candle.pha.pa.us>
Cc: Hiroshi Inoue <Inoue@tpf.co.jp>, Tom Lane <tgl@sss.pgh.pa.us>,
Thomas Lockhart <lockhart@alumni.caltech.edu>,
Peter Eisentraut
<peter_e@gmx.net>, Jan Wieck <JanWieck@Yahoo.com>,
PostgreSQL-development <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: RE: [HACKERS] Big 7.1 open items
Date: Tue, 27 Jun 2000 12:22:13 -0700
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> > > Well, I don't see any reason not to use tablespace/database
> > > rather than just tablespace. Seems having fewer files in
> > > each directory
> >
> > Once again - ability to use different tablespaces (disks)
> > for tables/indices in the same schema. Schemas must not dictate
> > where to store objects <- bad design.
>
> I am suggesting this symlink:
>
> ln -s data/base/testdb/myspace /var/myspace/testdb
>
> rather than:
>
> ln -s data/base/testdb/myspace /var/myspace
>
> Tablespaces still sit inside database directories, it is just that it
> points to a subdirectory of myspace, rather than myspace itself.
^^^^^^^^^^^
Didn't you mean
ln -s /var/myspace/testdb data/base/testdb/myspace
?
I thought that you don't like symlinks from data/base/... This is
how I understood Tom' words:
> The symlinks wouldn't do any good for what Bruce had in mind anyway
> (IIRC, he wanted to get useful per-database numbers from "du").
Vadim
From vmikheev@SECTORBASE.COM Tue Jun 27 15:43:31 2000
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From: "Mikheev, Vadim" <vmikheev@SECTORBASE.COM>
To: "'Bruce Momjian'" <pgman@candle.pha.pa.us>
Cc: "'Peter Eisentraut'" <peter_e@gmx.net>,
"'Hiroshi Inoue'"
<Inoue@tpf.co.jp>,
"'Tom Lane'" <tgl@sss.pgh.pa.us>,
Thomas Lockhart
<lockhart@alumni.caltech.edu>,
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Subject: RE: [HACKERS] Big 7.1 open items
Date: Tue, 27 Jun 2000 12:37:34 -0700
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> > > Then the system tables from different databases would collide.
> >
> > Actually, if we're going to use unique-ids for file names
> > then we have to know how to get system file names anyway.
> > Hm, OID+VERSION would make our life easier... Hiroshi?
>
> I assume we were going to have a pg_class.relversion to do that, but
^^^^^^^^
PG_CLASS_OID.VERSION_ID...
Just a clarification -:)
> that is per-database because pg_class is per-database.
Vadim
From vmikheev@SECTORBASE.COM Tue Jun 27 15:48:31 2000
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From: "Mikheev, Vadim" <vmikheev@SECTORBASE.COM>
To: "'Bruce Momjian'" <pgman@candle.pha.pa.us>
Cc: "'Peter Eisentraut'" <peter_e@gmx.net>,
"'Hiroshi Inoue'"
<Inoue@tpf.co.jp>,
"'Tom Lane'" <tgl@sss.pgh.pa.us>,
Thomas Lockhart
<lockhart@alumni.caltech.edu>,
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"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: RE: [HACKERS] Big 7.1 open items
Date: Tue, 27 Jun 2000 12:42:35 -0700
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> I actually meant I thought we were going to have a pg_class column
> called relversion that held the currently active version for that
> relation.
>
> Yes, the file name will be pg_class_oid.version_id.
>
> Is that OK?
We recently discussed pure *unique-id* file names...
Vadim
From pgsql-hackers-owner+M3939@hub.org Tue Jun 27 17:03:33 2000
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To: Peter Eisentraut <peter_e@gmx.net>
cc: "Mikheev, Vadim" <vmikheev@SECTORBASE.COM>,
"'Hiroshi Inoue'" <Inoue@tpf.co.jp>,
Thomas Lockhart <lockhart@alumni.caltech.edu>,
Bruce Momjian <pgman@candle.pha.pa.us>, Jan Wieck <JanWieck@Yahoo.com>,
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"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: Re: [HACKERS] Big 7.1 open items
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Comments: In-reply-to Peter Eisentraut <peter_e@gmx.net>
message dated "Tue, 27 Jun 2000 20:07:34 +0200"
Date: Tue, 27 Jun 2000 17:00:11 -0400
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From: Tom Lane <tgl@sss.pgh.pa.us>
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Peter Eisentraut <peter_e@gmx.net> writes:
> Mikheev, Vadim writes:
>> Do we need *both* database & tablespace to find table file ?!
>> Imho, database shouldn't be used...
> Then the system tables from different databases would collide.
I've been assuming that we would create a separate tablespace for
each database, which would be the location of that database's
system tables. It's probably also the default tablespace for user
tables created in that database, though it wouldn't have to be.
There should also be a known tablespace for the installation-wide tables
(pg_shadow et al).
With this approach tablespace+relation would indeed be a sufficient
identifier. We could even eliminate the knowledge that certain
tables are installation-wide from the bufmgr and below (currently
that knowledge is hardwired in places that I'd rather didn't know
about it...)
regards, tom lane
From tgl@sss.pgh.pa.us Tue Jun 27 17:00:13 2000
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To: Peter Eisentraut <peter_e@gmx.net>
cc: "Mikheev, Vadim" <vmikheev@SECTORBASE.COM>,
"'Hiroshi Inoue'" <Inoue@tpf.co.jp>,
Thomas Lockhart <lockhart@alumni.caltech.edu>,
Bruce Momjian <pgman@candle.pha.pa.us>, Jan Wieck <JanWieck@Yahoo.com>,
PostgreSQL-development <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: Re: [HACKERS] Big 7.1 open items
In-reply-to: <Pine.LNX.4.21.0006270326410.9749-100000@localhost.localdomain>
References: <Pine.LNX.4.21.0006270326410.9749-100000@localhost.localdomain>
Comments: In-reply-to Peter Eisentraut <peter_e@gmx.net>
message dated "Tue, 27 Jun 2000 20:07:34 +0200"
Date: Tue, 27 Jun 2000 17:00:11 -0400
Message-ID: <11132.962139611@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
Status: ROr
Peter Eisentraut <peter_e@gmx.net> writes:
> Mikheev, Vadim writes:
>> Do we need *both* database & tablespace to find table file ?!
>> Imho, database shouldn't be used...
> Then the system tables from different databases would collide.
I've been assuming that we would create a separate tablespace for
each database, which would be the location of that database's
system tables. It's probably also the default tablespace for user
tables created in that database, though it wouldn't have to be.
There should also be a known tablespace for the installation-wide tables
(pg_shadow et al).
With this approach tablespace+relation would indeed be a sufficient
identifier. We could even eliminate the knowledge that certain
tables are installation-wide from the bufmgr and below (currently
that knowledge is hardwired in places that I'd rather didn't know
about it...)
regards, tom lane
From tgl@sss.pgh.pa.us Tue Jun 27 17:18:49 2000
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To: Bruce Momjian <pgman@candle.pha.pa.us>
cc: "Mikheev, Vadim" <vmikheev@SECTORBASE.COM>,
"'Peter Eisentraut'" <peter_e@gmx.net>,
"'Hiroshi Inoue'" <Inoue@tpf.co.jp>,
Thomas Lockhart <lockhart@alumni.caltech.edu>,
Jan Wieck <JanWieck@Yahoo.com>,
PostgreSQL-development <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: Re: [HACKERS] Big 7.1 open items
In-reply-to: <200006271952.PAA05609@candle.pha.pa.us>
References: <200006271952.PAA05609@candle.pha.pa.us>
Comments: In-reply-to Bruce Momjian <pgman@candle.pha.pa.us>
message dated "Tue, 27 Jun 2000 15:52:40 -0400"
Date: Tue, 27 Jun 2000 17:19:31 -0400
Message-ID: <11374.962140771@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
Status: ROr
Bruce Momjian <pgman@candle.pha.pa.us> writes:
> Well, that would allow us to mix database files in the same directory,
> if we wanted to do that. My opinion it is better to keep databases in
> separate directories in each tablespace for clarity and performance
> reasons.
One reason not to do that is that we'd still have to special-case
the system-wide relations. If it's just tablespace and OID in the
path, then the system-wide rels look just the same as any other rel
as far as the low-level stuff is concerned. That would be nice.
My feeling about the "clarity and performance" issue is that if a
dbadmin wants to keep track of database contents separately, he can
put different databases' tables into different tablespaces to start
with. If he puts several tables into one tablespace, he's saying
he doesn't care about distinguishing their space usage. There's
no reason for us to force an additional level of directory lookup
to be done whether the admin wants it or not.
regards, tom lane
From tgl@sss.pgh.pa.us Tue Jun 27 17:29:35 2000
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To: Bruce Momjian <pgman@candle.pha.pa.us>
cc: "Mikheev, Vadim" <vmikheev@SECTORBASE.COM>,
"'Peter Eisentraut'" <peter_e@gmx.net>,
"'Hiroshi Inoue'" <Inoue@tpf.co.jp>,
Thomas Lockhart <lockhart@alumni.caltech.edu>,
Jan Wieck <JanWieck@Yahoo.com>,
PostgreSQL-development <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: Re: [HACKERS] Big 7.1 open items
In-reply-to: <200006272123.RAA09720@candle.pha.pa.us>
References: <200006272123.RAA09720@candle.pha.pa.us>
Comments: In-reply-to Bruce Momjian <pgman@candle.pha.pa.us>
message dated "Tue, 27 Jun 2000 17:23:49 -0400"
Date: Tue, 27 Jun 2000 17:30:17 -0400
Message-ID: <13018.962141417@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
Status: RO
Bruce Momjian <pgman@candle.pha.pa.us> writes:
> Yes, good point about pg_shadow. They don't have databases. How do we
> get multiple pg_class tables in the same directory? Is the
> pg_class.relversion file a number like 1,2,3,4, or does it come out of
> some global counter like oid. If so, we could put them in the same
> directory.
I think we could get away with insisting that each database store its
pg_class and friends in a separate tablespace (physically distinct
directory) from any other database. That gets around the OID conflict.
It's still an open question whether OID+version is better than
unique-ID for naming files that belong to different versions of the
same relation. I can see arguments on both sides.
regards, tom lane
From pgsql-hackers-owner+M3944@hub.org Tue Jun 27 17:33:05 2000
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To: Bruce Momjian <pgman@candle.pha.pa.us>
cc: "Mikheev, Vadim" <vmikheev@SECTORBASE.COM>,
"'Peter Eisentraut'" <peter_e@gmx.net>,
"'Hiroshi Inoue'" <Inoue@tpf.co.jp>,
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"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: Re: [HACKERS] Big 7.1 open items
In-reply-to: <200006272123.RAA09720@candle.pha.pa.us>
References: <200006272123.RAA09720@candle.pha.pa.us>
Comments: In-reply-to Bruce Momjian <pgman@candle.pha.pa.us>
message dated "Tue, 27 Jun 2000 17:23:49 -0400"
Date: Tue, 27 Jun 2000 17:30:17 -0400
Message-ID: <13018.962141417@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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Bruce Momjian <pgman@candle.pha.pa.us> writes:
> Yes, good point about pg_shadow. They don't have databases. How do we
> get multiple pg_class tables in the same directory? Is the
> pg_class.relversion file a number like 1,2,3,4, or does it come out of
> some global counter like oid. If so, we could put them in the same
> directory.
I think we could get away with insisting that each database store its
pg_class and friends in a separate tablespace (physically distinct
directory) from any other database. That gets around the OID conflict.
It's still an open question whether OID+version is better than
unique-ID for naming files that belong to different versions of the
same relation. I can see arguments on both sides.
regards, tom lane
From Inoue@tpf.co.jp Tue Jun 27 19:13:30 2000
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Date: Wed, 28 Jun 2000 08:16:27 +0900
From: Hiroshi Inoue <Inoue@tpf.co.jp>
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To: Tom Lane <tgl@sss.pgh.pa.us>
CC: Bruce Momjian <pgman@candle.pha.pa.us>,
"Mikheev, Vadim" <vmikheev@SECTORBASE.COM>,
"'Peter Eisentraut'" <peter_e@gmx.net>,
Thomas Lockhart <lockhart@alumni.caltech.edu>,
Jan Wieck <JanWieck@Yahoo.com>,
PostgreSQL-development <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: Re: [HACKERS] Big 7.1 open items
References: <200006272123.RAA09720@candle.pha.pa.us> <13018.962141417@sss.pgh.pa.us>
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Status: RO
Tom Lane wrote:
> Bruce Momjian <pgman@candle.pha.pa.us> writes:
> > Yes, good point about pg_shadow. They don't have databases. How do we
> > get multiple pg_class tables in the same directory? Is the
> > pg_class.relversion file a number like 1,2,3,4, or does it come out of
> > some global counter like oid. If so, we could put them in the same
> > directory.
>
> I think we could get away with insisting that each database store its
> pg_class and friends in a separate tablespace (physically distinct
> directory) from any other database. That gets around the OID conflict.
>
> It's still an open question whether OID+version is better than
> unique-ID for naming files that belong to different versions of the
> same relation. I can see arguments on both sides.
>
I don't stick to unique-ID. My main point has always been the
transactional control of file allocation change.
However *VERSION(_ID)* may be misleading because it couldn't
mean the version of pg_class tuples.
Regards.
Hiroshi Inoue
Inoue@tpf.co.jp
From tgl@sss.pgh.pa.us Wed Jun 28 12:10:59 2000
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To: Bruce Momjian <pgman@candle.pha.pa.us>
cc: "Mikheev, Vadim" <vmikheev@SECTORBASE.COM>,
"'Peter Eisentraut'" <peter_e@gmx.net>,
"'Hiroshi Inoue'" <Inoue@tpf.co.jp>,
Thomas Lockhart <lockhart@alumni.caltech.edu>,
Jan Wieck <JanWieck@Yahoo.com>,
PostgreSQL-development <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: Re: [HACKERS] Big 7.1 open items
In-reply-to: <200006281425.KAA05633@candle.pha.pa.us>
References: <200006281425.KAA05633@candle.pha.pa.us>
Comments: In-reply-to Bruce Momjian <pgman@candle.pha.pa.us>
message dated "Wed, 28 Jun 2000 10:25:21 -0400"
Date: Wed, 28 Jun 2000 12:11:40 -0400
Message-ID: <15787.962208700@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
Status: ROr
Bruce Momjian <pgman@candle.pha.pa.us> writes:
> If we put multiple database tables in the same directory, have we
> considered how to drop databases? Right now we do rm -rf:
rm -rf will no longer work in a tablespaces environment anyway.
(Even if you kept symlinks underneath the DB directory, rm -rf
wouldn't follow them.)
DROP DATABASE will have to be implemented honestly: run through
pg_class and do a regular DROP on each user table.
Once you've got rid of the user tables, rm -rf should suffice to
get rid of the "home tablespace" as I've been calling it, with
all the system tables therein.
Now that you mention it, this is another reason why system tables for
each database have to live in a separate tablespace directory: there's
no other good way to do that final stage of DROP DATABASE. The
DROP-each-table approach doesn't work for system tables (somewhere along
about the point where you drop pg_attribute, DROP TABLE itself would
stop working ;-)).
However I do see a bit of a problem here: since DROP DATABASE is
ordinarily executed by a backend that's running in a different database,
how's it going to read pg_class of the target database? Perhaps it will
be necessary to fire up a sub-backend that runs in the target DB for
long enough to kill all the user tables. Looking messy...
regards, tom lane
From pgsql-hackers-owner+M3998@hub.org Wed Jun 28 19:53:28 2000
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Date: Thu, 29 Jun 2000 08:53:03 +0900
From: Hiroshi Inoue <Inoue@tpf.co.jp>
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To: Tom Lane <tgl@sss.pgh.pa.us>
CC: Bruce Momjian <pgman@candle.pha.pa.us>,
"Mikheev, Vadim" <vmikheev@SECTORBASE.COM>,
"'Peter Eisentraut'" <peter_e@gmx.net>,
Thomas Lockhart <lockhart@alumni.caltech.edu>,
Jan Wieck <JanWieck@Yahoo.com>,
PostgreSQL-development <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: Re: [HACKERS] Big 7.1 open items
References: <EKEJJICOHDIEMGPNIFIJGEHCCCAA.Inoue@tpf.co.jp> <16404.962213972@sss.pgh.pa.us>
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Tom Lane wrote:
> "Hiroshi Inoue" <Inoue@tpf.co.jp> writes:
> > Why do we have to have system tables per *database* ?
> > Is there anything wrong with global system tables ?
> > And how about adding dbid to pg_class,pg_proc etc ?
>
> We could, but I think I'd vote against it on two grounds:
>
> 1. Reliability. If something corrupts pg_class, do you want to
> lose your whole installation, or just one database?
>
> 2. Increased locking overhead/loss of concurrency. Currently, there
> is very little lock contention between backends running in different
> databases. A shared pg_class will be a single point of locking (as
> well as a single point of failure) for the whole installation.
Isn't current design of PG's *database* for dropdb using "rm -rf"
rather than for above 1.2. ?
If we couldn't rely on our db itself and our locking mechanism is
poor,we could start different postmasters for different *database*s.
> It would solve the DROP DATABASE problem kind of nicely, but really
> it'd just be downgrading DROP DATABASE to a DROP SCHEMA operation...
>
What is our *DATABASE* ?
Is it clear to all people ?
At least it's a vague concept for me.
Could you please tell me what kind of objects are our *DATABASE*
objects but could not be schema objects ?
Regards.
Hiroshi Inoue
From pgsql-hackers-owner+M4003@hub.org Thu Jun 29 10:41:19 2000
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From: Zeugswetter Andreas SB <ZeugswetterA@wien.spardat.at>
To: "'Bruce Momjian'" <pgman@candle.pha.pa.us>
Cc: "Mikheev, Vadim" <vmikheev@SECTORBASE.COM>,
Hiroshi Inoue
<Inoue@tpf.co.jp>, Tom Lane <tgl@sss.pgh.pa.us>,
Thomas Lockhart
<lockhart@alumni.caltech.edu>,
Peter Eisentraut <peter_e@gmx.net>, Jan Wieck <JanWieck@Yahoo.com>,
PostgreSQL-development
<pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: AW: AW: [HACKERS] Big 7.1 open items
Date: Thu, 29 Jun 2000 09:43:14 +0200
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> > ln -s data/base/testdb/myspace/extent1 /var/myspace/extent1/testdb
>
> The idea was to put the main files in the directory, and create Extent2,
> Extent3 directories for the extents.
The reasoning was, that the database subdir should be below the extentdir,
so that creating different fs for each extent would be easier, and not
depend
on the database name.
It is easy to create fs for:
/var/myspace
or
/var/myspace[/extent1]
/var/myspace/extent2
but not if it has dbname in it.
Andreas
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From: Zeugswetter Andreas SB <ZeugswetterA@wien.spardat.at>
To: "'Tom Lane'" <tgl@sss.pgh.pa.us>
Cc: "'Bruce Momjian'" <pgman@candle.pha.pa.us>,
Peter Eisentraut
<peter_e@gmx.net>,
"Mikheev, Vadim" <vmikheev@SECTORBASE.COM>,
"'Hiroshi Inoue'" <Inoue@tpf.co.jp>,
Thomas Lockhart
<lockhart@alumni.caltech.edu>,
Jan Wieck <JanWieck@yahoo.com>,
PostgreSQL-development <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: AW: AW: [HACKERS] Big 7.1 open items
Date: Thu, 29 Jun 2000 12:33:39 +0200
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> > > I think I would prefer the ability to place more than one
> > database into
> > > the same tablespace.
> >
> > You can put user tables from multiple databases into the same
> > tablespace, under this proposal. Just not system tables.
>
> Yes, but then it is only half baked.
Half baked or not, I think I am starting to like it.
I think I would restrict such an automagically created tablespace
(tblspace name = db name) to only contain tables from this database.
Andreas
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Date: Thu, 29 Jun 2000 19:27:15 +0200 (CEST)
From: Peter Eisentraut <peter_e@gmx.net>
To: Hiroshi Inoue <Inoue@tpf.co.jp>
cc: Zeugswetter Andreas SB <ZeugswetterA@wien.spardat.at>,
"'Mikheev, Vadim'" <vmikheev@SECTORBASE.COM>,
PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: AW: [HACKERS] Big 7.1 open items
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Hiroshi Inoue writes:
> According to your another posting,your *database* hierarchy is
> instance -> database -> schema -> object
> like Oracle.
>
> However SQL92 seems to have another hierarchy:
> cluster -> catalog -> schema -> object
> and dot notation catalog.schema.object could be used.
FYI:
An "instance" is a "cluster". I don't know where the word instance came
from, the docs sometimes call it "installation" or "site", which is even
worse. I have been using "database cluster" for the latest documentation
work. My dictionary defines a cluster as "a group of things gathered or
occurring closely together", which is what this is. Call it a "data area"
or an "initdb'ed thing", etc.
A "catalog" can be equated with our "database". The method of creating
catalogs is implementation defined, so our CREATE DATABASE command is in
perfect compliance with the standard. We don't support the
catalog.schema.object notation but that notation only makes sense when you
can access more than one catalog at a time. We don't allow that and SQL
doesn't require it. We could allow that notation and throw an error when
the catalog name doesn't match the current database, but that's mere
cosmetic work.
In entry level SQL 92, a "schema" is essentially the same as table
ownership. You can execute the command CREATE SCHEMA AUTHORIZATION
"peter", which means that user "peter" (where he came from is
"implementation-defined") can now create tables under his name. There is
no such thing as a table owner, there's the "containing schema" and its
owner. The tables "peter" creates can then be referenced by the dotted
notation. But it is not correct to equate this with CREATE USER. Even if
there was no schema for "peter" he could still connect and query other
people's tables.
Moving beyond SQL 92 you can also create schemas with a different name
than your user name. This is merely a little more naming flexibility.
--
Peter Eisentraut Sernanders v<>g 10:115
peter_e@gmx.net 75262 Uppsala
http://yi.org/peter-e/ Sweden
From peter@localhost.its.uu.se Thu Jun 29 19:25:40 2000
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Date: Fri, 30 Jun 2000 01:32:20 +0200 (CEST)
From: Peter Eisentraut <peter_e@gmx.net>
To: Tom Lane <tgl@sss.pgh.pa.us>
cc: "Mikheev, Vadim" <vmikheev@SECTORBASE.COM>,
"'Hiroshi Inoue'" <Inoue@tpf.co.jp>,
Thomas Lockhart <lockhart@alumni.caltech.edu>,
Bruce Momjian <pgman@candle.pha.pa.us>, Jan Wieck <JanWieck@yahoo.com>,
PostgreSQL-development <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: Re: [HACKERS] Big 7.1 open items
In-Reply-To: <17726.962240702@sss.pgh.pa.us>
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Tom Lane writes:
> You can put *user* tables from more than one database into a table space.
> The restriction is just on *system* tables.
I think my understanding as a user would be that a table space represents
a storage location. If I want to put a table/object/entire database on a
fancy disk somewhere I create a table space for it there. But if I want to
store all my stuff under /usr/local/pgsql/data then I wouldn't expect to
have to create more than one table space. So the table spaces become at
that point affected by the logical hierarchy: I must make sure to have
enough table spaces to have many databases.
More specifically, what would the user interface to this look like?
Clearly there has to be some sort of CREATE TABLESPACE command. Now does
CREATE DATABASE imply a CREATE TABLESPACE? I think not. Do you have to
create a table space before creating each database? I think not.
> We could avoid it along the lines you suggest (name table files like
> DBOID.RELOID.VERSION instead of just RELOID.VERSION) but is it really
> worth it?
I only intended that for pg_class and other bootstrap-sort-of tables,
maybe all system tables. Normal heap files could look like RELOID.VERSION,
whereas system tables would look like "name.DBOID". Clearly there's no
market for renaming system tables or dropping any of their columns. We're
obviously going to have to treat pg_class special anyway.
> Vadim's concerned about every byte that has to go into the WAL log,
> and I think he's got a good point.
True. But if you only do it for the system tables then it might take less
space than keeping track of lots of table spaces that are unneeded. :-)
--
Peter Eisentraut Sernanders v<>g 10:115
peter_e@gmx.net 75262 Uppsala
http://yi.org/peter-e/ Sweden
From pgsql-hackers-owner+M4032@hub.org Thu Jun 29 20:12:39 2000
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Date: Fri, 30 Jun 2000 08:59:49 +0900
From: Hiroshi Inoue <Inoue@tpf.co.jp>
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To: Peter Eisentraut <peter_e@gmx.net>
CC: Zeugswetter Andreas SB <ZeugswetterA@wien.spardat.at>,
"'Mikheev, Vadim'" <vmikheev@SECTORBASE.COM>,
PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: AW: [HACKERS] Big 7.1 open items
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Peter Eisentraut wrote:
> Hiroshi Inoue writes:
>
> > According to your another posting,your *database* hierarchy is
> > instance -> database -> schema -> object
> > like Oracle.
> >
> > However SQL92 seems to have another hierarchy:
> > cluster -> catalog -> schema -> object
> > and dot notation catalog.schema.object could be used.
>
> FYI:
Thanks.
I'm asking to all what our *DATABASE* is.
Different from you,I couldn't see any decisive feature in our *DATABASE*.
>
>
> An "instance" is a "cluster". I don't know where the word instance came
I could find the word in Oracle.
IMHO,it corresponds to our initdb'ed thing(a postmaster controls).
>
> from, the docs sometimes call it "installation" or "site", which is even
> worse. I have been using "database cluster" for the latest documentation
> work. My dictionary defines a cluster as "a group of things gathered or
> occurring closely together", which is what this is. Call it a "data area"
> or an "initdb'ed thing", etc.
>
SQL92 seems to say that a cluster corresponds to a target of connection
and has no name(after connection was established). Isn't it same as our
*DATABASE* ?
>
> A "catalog" can be equated with our "database". The method of creating
> catalogs is implementation defined, so our CREATE DATABASE command is in
> perfect compliance with the standard. We don't support the
> catalog.schema.object notation but that notation only makes sense when you
> can access more than one catalog at a time.
Yes,it's most essential that we couldn't access more than one catalog.
This means that we have only one (noname) "catalog" per "cluster".
> We don't allow that and SQL
> doesn't require it. We could allow that notation and throw an error when
> the catalog name doesn't match the current database, but that's mere
> cosmetic work.
>
> In entry level SQL 92, a "schema" is essentially the same as table
> ownership. You can execute the command CREATE SCHEMA AUTHORIZATION
> "peter", which means that user "peter" (where he came from is
> "implementation-defined") can now create tables under his name. There is
> no such thing as a table owner, there's the "containing schema" and its
> owner. The tables "peter" creates can then be referenced by the dotted
> notation. But it is not correct to equate this with CREATE USER. Even if
> there was no schema for "peter" he could still connect and query other
> people's tables.
>
I've used *username* "schema"s in Oracle for a long time but I've never
thought that it's the essence of "schema". If I recoginze correctly,the
concept of "catalog" hasn't necessarily been important while "schema"
= "user". The conflict of "schema" name is equivalent to the conflict
of "user" name if "schema" = "user". IMHO,SQL92 has required the
concept of "catalog" because "schema" has been changed to be
independent of "user".
Anyway in current PG "cluster":"catalog":"schema"=1:1:1(0) and
our *DATABASE* is an only confusing concept in the hierarchy..
Regards,
Hiroshi Inoue
From tgl@sss.pgh.pa.us Thu Jun 29 20:42:56 2000
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To: Peter Eisentraut <peter_e@gmx.net>
cc: "Mikheev, Vadim" <vmikheev@SECTORBASE.COM>,
"'Hiroshi Inoue'" <Inoue@tpf.co.jp>,
Thomas Lockhart <lockhart@alumni.caltech.edu>,
Bruce Momjian <pgman@candle.pha.pa.us>, Jan Wieck <JanWieck@yahoo.com>,
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Subject: Re: [HACKERS] Big 7.1 open items
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Comments: In-reply-to Peter Eisentraut <peter_e@gmx.net>
message dated "Fri, 30 Jun 2000 01:32:20 +0200"
Date: Thu, 29 Jun 2000 20:43:32 -0400
Message-ID: <2517.962325812@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
Status: RO
Peter Eisentraut <peter_e@gmx.net> writes:
> Tom Lane writes:
>> You can put *user* tables from more than one database into a table space.
>> The restriction is just on *system* tables.
> More specifically, what would the user interface to this look like?
> Clearly there has to be some sort of CREATE TABLESPACE command. Now does
> CREATE DATABASE imply a CREATE TABLESPACE? I think not. Do you have to
> create a table space before creating each database? I think not.
I would say that CREATE DATABASE just implicitly creates a new
tablespace that's physically located right under the toplevel data
directory of the installation, no symlink. What's wrong with that?
You need not keep anything except the system tables of the DB there
if you don't want to. In practice, for someone who doesn't need to
worry about tablespaces (because they put the installation on a disk
with enough room for their purposes), the whole thing acts exactly
the same as it does now.
>> We could avoid it along the lines you suggest (name table files like
>> DBOID.RELOID.VERSION instead of just RELOID.VERSION) but is it really
>> worth it?
> I only intended that for pg_class and other bootstrap-sort-of tables,
> maybe all system tables. Normal heap files could look like RELOID.VERSION,
> whereas system tables would look like "name.DBOID".
That would imply that the very bottom levels of the system know all
about which tables are system tables and which are not (and, if you
are really going to insist on the "name" part of that, that they
know what name goes with each system-table OID). I'd prefer to avoid
that. The less the smgr knows about the upper levels of the system,
the better.
> Clearly there's no market for renaming system tables or dropping any
> of their columns.
No, but there is a market for compacting indexes on system relations,
and I haven't heard a good proposal for doing index compaction in place.
So we need versioning for system indexes.
>> Vadim's concerned about every byte that has to go into the WAL log,
>> and I think he's got a good point.
> True. But if you only do it for the system tables then it might take less
> space than keeping track of lots of table spaces that are unneeded. :-)
Again, WAL should not need to distinguish system and user tables.
And as for the keeping track, the tablespace OID will simply replace the
database OID in the log and in the smgr interfaces. There's no "extra"
cost, except maybe by comparison to a system with neither tablespaces
nor multiple databases.
regards, tom lane
From peter@localhost.its.uu.se Sat Jul 1 10:39:11 2000
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Date: Sat, 1 Jul 2000 17:03:42 +0200 (CEST)
From: Peter Eisentraut <peter_e@gmx.net>
To: Tom Lane <tgl@sss.pgh.pa.us>
cc: "Mikheev, Vadim" <vmikheev@SECTORBASE.COM>,
"'Hiroshi Inoue'" <Inoue@tpf.co.jp>,
Thomas Lockhart <lockhart@alumni.caltech.edu>,
Bruce Momjian <pgman@candle.pha.pa.us>, Jan Wieck <JanWieck@yahoo.com>,
PostgreSQL-development <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: Re: [HACKERS] Big 7.1 open items
In-Reply-To: <2517.962325812@sss.pgh.pa.us>
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Tom Lane writes:
> In practice, for someone who doesn't need to worry about tablespaces
> (because they put the installation on a disk with enough room for
> their purposes), the whole thing acts exactly the same as it does now.
But I'd venture the guess that for someone who wants to use tablespaces it
wouldn't work as expected. Table spaces should represent a physical
storage location. Creation of table spaces should be a restricted
operation, possibly more than, but at least differently from, databases.
Eventually, table spaces probably will have attributes, such as
optimization parameters (random_page_cost). This will not work as expected
if you intermix them with the databases.
I'd expect that if I have three disks and 50 databases, then I make three
tablespaces and assign the databases to them. I'll bet lunch that if we
don't do it that way that before long people will come along and ask for
something that does work this way.
--
Peter Eisentraut Sernanders v<>g 10:115
peter_e@gmx.net 75262 Uppsala
http://yi.org/peter-e/ Sweden
From pgsql-hackers-owner+M4066@hub.org Sat Jul 1 13:21:39 2000
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To: Peter Eisentraut <peter_e@gmx.net>
cc: "Mikheev, Vadim" <vmikheev@SECTORBASE.COM>,
"'Hiroshi Inoue'" <Inoue@tpf.co.jp>,
Thomas Lockhart <lockhart@alumni.caltech.edu>,
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Subject: Re: [HACKERS] Big 7.1 open items
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Comments: In-reply-to Peter Eisentraut <peter_e@gmx.net>
message dated "Sat, 01 Jul 2000 17:03:42 +0200"
Date: Sat, 01 Jul 2000 13:37:21 -0400
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From: Tom Lane <tgl@sss.pgh.pa.us>
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Peter Eisentraut <peter_e@gmx.net> writes:
> I'd expect that if I have three disks and 50 databases, then I make three
> tablespaces and assign the databases to them.
In our last installment, you were complaining that you didn't want to
be bothered with that ;-)
But I don't see any reason why CREATE DATABASE couldn't take optional
parameters indicating where to create the new DB's default tablespace.
We already have a LOCATION option for it that does something close to
that.
Come to think of it, it would probably make sense to adapt the existing
notion of "location" (cf initlocation script) into something meaning
"directory that users are allowed to create tablespaces (including
databases) in". If there were an explicit table of allowed locations,
it could be used to address the protection issues you raise --- for
example, a location could be restricted so that only some users could
create tablespaces/databases in it. $PGDATA/data would be just the
first location in every installation.
regards, tom lane
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To: Tom Lane <tgl@sss.pgh.pa.us>
cc: "Mikheev, Vadim" <vmikheev@SECTORBASE.COM>,
"'Hiroshi Inoue'" <Inoue@tpf.co.jp>,
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Bruce Momjian <pgman@candle.pha.pa.us>, Jan Wieck <JanWieck@yahoo.com>,
PostgreSQL-development <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: Re: [HACKERS] Big 7.1 open items
In-Reply-To: <22819.962473041@sss.pgh.pa.us>
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Tom Lane writes:
> Come to think of it, it would probably make sense to adapt the existing
> notion of "location" (cf initlocation script) into something meaning
> "directory that users are allowed to create tablespaces (including
> databases) in".
This is what I've been trying to push all along. But note that this
mechanism does allow multiple databases per location. :)
--
Peter Eisentraut Sernanders v<>g 10:115
peter_e@gmx.net 75262 Uppsala
http://yi.org/peter-e/ Sweden
From ZeugswetterA@wien.spardat.at Mon Jul 3 04:30:07 2000
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From: Zeugswetter Andreas SB <ZeugswetterA@wien.spardat.at>
To: "'Hiroshi Inoue'" <Inoue@seiren.co.jp>,
Peter Eisentraut
<peter_e@gmx.net>, Tom Lane <tgl@sss.pgh.pa.us>
Cc: Bruce Momjian <pgman@candle.pha.pa.us>, Jan Wieck <JanWieck@Yahoo.com>,
PostgreSQL-development <pgsql-hackers@postgresql.org>,
"Ross J. Reedstrom" <reedstrm@rice.edu>
Subject: AW: [HACKERS] Big 7.1 open items
Date: Mon, 3 Jul 2000 10:28:05 +0200
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> > > > > In my mind the point of the "database" concept is to
> > > provide a domain
> > > > > within which custom datatypes and functions are available.
> > > >
> > >
> > > AFAIK few users understand it and many users have wondered
> > > why we couldn't issue cross "database" queries.
> >
> > Imho the same issue is access to tables on another machine.
> > If we "fix" that, access to another db on the same instance is just
> > a variant of the above.
> >
>
> What is a difference between SCHAMA and your "database" ?
> I myself am confused about them.
"my *database*" corresponds to the current database, which is created with
"create database" in postgresql. It corresponds to the catalog concept in
SQL99.
The schema is below the database. Access to different schemas with one
connection
is mandatory. Access to different catalogs (databases) with one connection
is not mandatory,
but should imho be solved analogous to access to another catalog on a
different
(SQL99) cluster. This would be a very nifty feature.
Andreas
From pgsql-hackers-owner+M3496@hub.org Fri Jun 16 15:55:14 2000
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To: pgsql-hackers@postgresql.org
Subject: [HACKERS] OK, OK, Hiroshi's right: use a seperately-generated filename
Date: Fri, 16 Jun 2000 13:51:37 -0400
Message-ID: <7942.961177897@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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After further thought I think there's a lot of merit in Hiroshi's
opinion that physical file names should not be tied to relation OID.
If we use a separately generated value for the file name, we can
solve a lot of problems pretty nicely by means of "table versioning".
For example: VACUUM can't compact indexes at the moment, and what it
does do (scan the index and delete unused entries) is really slow.
The right thing to do is for it to generate an all-new index file,
but how do we do that without creating a risk of leaving the index
corrupted if we crash partway through? The answer is to build the
new index in a new physical file. But how do we install the new
file as the real index atomically, when it might span multiple
segments? If the physical file name is decoupled from the relation's
name *and* OID then there is no problem: the atomic event that makes
the new file(s) the real table contents is the commit of the new
pg_class row with the new value for the physical filename.
Aside from possible improvements in VACUUM, this would let us do a
robust implementation of CLUSTER, and we could do the "really change
the table" variant of ALTER TABLE DROP COLUMN the same way if anyone
wants to do it.
The only cost is that we need an additional column in pg_class to
hold the physical file name. That's not so bad, especially when
you remember that we'd surely need to add something to pg_class for
tablespace support anyway.
If we bite that bullet, then we could also do something to satisfy
Bruce about having legible file names ;-). The column in pg_class
could perfectly well be a string, not a pure number, and that means
that we can throw in the relname (truncated to fit of course). So
the thing would act a lot like the original-relname-plus-OID variant
that's been discussed so far. (Original relname because ALTER TABLE
RENAME would *not* change the physical file name. But we could
think about a form of VACUUM that creates a whole new table by
versioning, and that would presumably bring the physical name back
in sync with the logical relname.)
Here is a sketch of a concrete proposal. I see no need to have
separate pg_class columns for tablespace and physical relname;
instead, I suggest there be a column of type NAME that is the
file pathname (relative to the database directory). Further,
instead of the existing convention of appending .N to the base
file name to make extension segment names, I propose that we
always have a segment number in the physical file name, and that
the pg_class entry be required to contain a "%d" somewhere that
indicates where. The actual filename is manufactured by
sprintf(tempbuf, value_from_pg_class_column, segment_number);
As an example, the arrangement I was suggesting earlier today
about segments in different subdirectories of a tablespace
could be implemented by assigning physical filenames like
tablespace/%d/12345_relname
where the 12345 is a value generated separately from the table's OID.
(We would still use the OID counter to produce these numbers, and
in fact there's no reason not to use the table's OID as the initial
unique ID for the physical filename. The point is just that the
physical filename doesn't have to remain forever equal to the
relation's OID.)
If we use type NAME for this string then the tablespace part of the path
would have to be kept to no more than ~ 15 characters, but that seems
workable enough. (Anybody who really didn't like that could recompile
with larger NAMEDATALEN. Doesn't seem worth inventing a separate type.)
As Hiroshi pointed out, one of the best aspects of this approach
is that the physical table layout policy doesn't have to be hard-wired
into low-level file access routines. The low-level routines don't
need to know much of anything about the format of the pathname,
they just stuff in the right segment number and use the name. The
layout policy need only be known to one single routine that generates
the strings that go into pg_class. So it'd be really easy to change.
One thing we'd have to work out is that the critical system tables
(eg, pg_class itself, as well as its indexes) would have to have
predictable physical names. Otherwise there's no way for a new
backend to bootstrap itself up ... it can't very well read pg_class
to find out where pg_class is. A brute-force solution is to forbid
reversioning of the critical tables, but I suspect we can find a
less restrictive answer.
This seems like it'd satisfy all the concerns that have been raised.
Comments?
regards, tom lane
From pgsql-hackers-owner+M3524@hub.org Fri Jun 16 22:30:59 2000
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To: Chris Bitmead <chris@bitmead.com>
cc: pgsql-hackers@postgreSQL.org
Subject: Re: [HACKERS] OK, OK, Hiroshi's right: use a seperately-generated filename
In-reply-to: <394ACB42.C87C59B8@bitmead.com>
References: <7942.961177897@sss.pgh.pa.us> <394ACB42.C87C59B8@bitmead.com>
Comments: In-reply-to Chris Bitmead <chris@bitmead.com>
message dated "Sat, 17 Jun 2000 10:50:10 +1000"
Date: Fri, 16 Jun 2000 21:12:29 -0400
Message-ID: <10206.961204349@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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Chris Bitmead <chris@bitmead.com> writes:
> At least on UNIX, couldn't you use a hard-link and change the name in
> pg_class immediately? Let the brain-dead operating systems use the
> vacuum method.
Hmm ... maybe, but it doesn't seem worth the portability headache to
me. We do have an NT port that we don't want to break, and I don't
think RENAME TABLE is worth the trouble of testing/supporting two
implementations.
Even on Unix, aren't there filesystems that don't do hard links?
Not that I'd recommend running Postgres on such a volume, but...
regards, tom lane
From pgsql-hackers-owner+M3525@hub.org Sat Jun 17 07:01:03 2000
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From: "Hiroshi Inoue" <Inoue@tpf.co.jp>
To: "Tom Lane" <tgl@sss.pgh.pa.us>
Cc: <pgsql-hackers@postgresql.org>
Subject: RE: [HACKERS] OK, OK, Hiroshi's right: use a seperately-generated filename
Date: Sat, 17 Jun 2000 18:38:53 +0900
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> -----Original Message-----
> From: pgsql-hackers-owner@hub.org [mailto:pgsql-hackers-owner@hub.org]On
> Behalf Of Tom Lane
>
> After further thought I think there's a lot of merit in Hiroshi's
> opinion that physical file names should not be tied to relation OID.
> If we use a separately generated value for the file name, we can
> solve a lot of problems pretty nicely by means of "table versioning".
>
> For example: VACUUM can't compact indexes at the moment, and what it
> does do (scan the index and delete unused entries) is really slow.
> The right thing to do is for it to generate an all-new index file,
> but how do we do that without creating a risk of leaving the index
> corrupted if we crash partway through? The answer is to build the
> new index in a new physical file. But how do we install the new
> file as the real index atomically, when it might span multiple
> segments? If the physical file name is decoupled from the relation's
> name *and* OID then there is no problem: the atomic event that makes
> the new file(s) the real table contents is the commit of the new
> pg_class row with the new value for the physical filename.
>
> Aside from possible improvements in VACUUM, this would let us do a
> robust implementation of CLUSTER, and we could do the "really change
> the table" variant of ALTER TABLE DROP COLUMN the same way if anyone
> wants to do it.
>
Yes,I've wondered how do we implement column_is_really_dropped
ALTER TABLE DROP COLUMN feature without this kind of mechanism.
> The only cost is that we need an additional column in pg_class to
> hold the physical file name. That's not so bad, especially when
> you remember that we'd surely need to add something to pg_class for
> tablespace support anyway.
>
> If we bite that bullet, then we could also do something to satisfy
> Bruce about having legible file names ;-). The column in pg_class
> could perfectly well be a string, not a pure number, and that means
> that we can throw in the relname (truncated to fit of course). So
> the thing would act a lot like the original-relname-plus-OID variant
> that's been discussed so far. (Original relname because ALTER TABLE
> RENAME would *not* change the physical file name. But we could
> think about a form of VACUUM that creates a whole new table by
> versioning, and that would presumably bring the physical name back
> in sync with the logical relname.)
>
> As Hiroshi pointed out, one of the best aspects of this approach
> is that the physical table layout policy doesn't have to be hard-wired
> into low-level file access routines. The low-level routines don't
> need to know much of anything about the format of the pathname,
> they just stuff in the right segment number and use the name. The
> layout policy need only be known to one single routine that generates
> the strings that go into pg_class. So it'd be really easy to change.
>
Ross's approach is fundamentally same though he is using relname+OID
naming rule. I've said his trial is most practical one.
> One thing we'd have to work out is that the critical system tables
> (eg, pg_class itself, as well as its indexes) would have to have
> predictable physical names.
The only limitation of the relation filename is the uniqueness.
So it doesn't introduce any inconsistency that system tables
have fixed name.
As for system relations it wouldn't be so bad because CLUSTER/
ALTER TABLE DROP COLUMN ... would be unnecessary(maybe).
But as for system indexes,it is preferable that VACUUM/REINDEX
could rebuild them safely. System indexes never shrink currently.
Regards.
Hiroshi Inoue
Inoue@tpf.co.jp
From pgsql-hackers-owner+M3529@hub.org Sat Jun 17 10:01:24 2000
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Date: Sat, 17 Jun 2000 15:01:53 +0200 (CEST)
From: Peter Eisentraut <peter_e@gmx.net>
To: Tom Lane <tgl@sss.pgh.pa.us>
cc: pgsql-hackers@postgreSQL.org
Subject: Re: [HACKERS] OK, OK, Hiroshi's right: use a seperately-generated
filename
In-Reply-To: <7942.961177897@sss.pgh.pa.us>
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Tom Lane writes:
> tablespace/%d/12345_relname
Throwing table spaces and relation names into one pot doesn't excite me
very much. For example, before long people will want to
* Query what tables are in what space (without using string operations)
Consider for example creating a new table and choosing where to put it.
* Rename table spaces
* Assign attributes of some sort to table spaces (permissions, etc.)
* Use table space names with more than 15 characters. :)
Somehow table spaces need to be catalogued. You could still make the
physical file name 'tablespaceoid/rest' without actually having to look up
anything, although that depends on your symlink idea which is still under
discussion.
Then, why are all nth segments of tables in one directory in that
proposal?
Also, you said before that an old relname (after rename) is worse than
none at all. I couldn't agree more.
Why not use OID.[SEGMENT.]VERSION for the physical relname (different
order possible)? That way you at least have some guaranteed correspondence
between files and tables. Version could probably be an INT2, so you save
some space.
--
Peter Eisentraut Sernanders v<>g 10:115
peter_e@gmx.net 75262 Uppsala
http://yi.org/peter-e/ Sweden
From pgsql-hackers-owner+M3534@hub.org Sat Jun 17 13:31:11 2000
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To: "Hiroshi Inoue" <Inoue@tpf.co.jp>
cc: pgsql-hackers@postgreSQL.org
Subject: Re: [HACKERS] OK, OK, Hiroshi's right: use a seperately-generated filename
In-reply-to: <EKEJJICOHDIEMGPNIFIJIEAKCCAA.Inoue@tpf.co.jp>
References: <EKEJJICOHDIEMGPNIFIJIEAKCCAA.Inoue@tpf.co.jp>
Comments: In-reply-to "Hiroshi Inoue" <Inoue@tpf.co.jp>
message dated "Sat, 17 Jun 2000 18:38:53 +0900"
Date: Sat, 17 Jun 2000 12:24:56 -0400
Message-ID: <18936.961259096@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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"Hiroshi Inoue" <Inoue@tpf.co.jp> writes:
>> One thing we'd have to work out is that the critical system tables
>> (eg, pg_class itself, as well as its indexes) would have to have
>> predictable physical names.
> The only limitation of the relation filename is the uniqueness.
> So it doesn't introduce any inconsistency that system tables
> have fixed name.
> As for system relations it wouldn't be so bad because CLUSTER/
> ALTER TABLE DROP COLUMN ... would be unnecessary(maybe).
> But as for system indexes,it is preferable that VACUUM/REINDEX
> could rebuild them safely. System indexes never shrink currently.
Right, it's the index-shrinking business that has me worried.
Most of the other reasons for swapping in a new file don't apply
to system tables, but that one does.
One possibility is to say that system *tables* can't be reversioned
(at least not the critical ones) but system *indexes* can be.
Then we'd have to use your ignore-system-indexes stuff during backend
startup, until we'd found out where the indexes are. Might be too big
a time penalty however... not sure. Shared cache inval of a system
index could be a little tricky too; I don't think the catcache routines
are prepared to fall back to non-index scan are they?
On the whole it might be better to cheat by using a side data structure
like the pg_internal.init file, that a backend could consult to find out
where the indexes are now.
regards, tom lane
From pgsql-hackers-owner+M3553@hub.org Sun Jun 18 18:31:03 2000
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From: Peter Eisentraut <peter_e@gmx.net>
To: Tom Lane <tgl@sss.pgh.pa.us>
cc: PostgreSQL Development <pgsql-hackers@postgresql.org>
Subject: Re: [HACKERS] OK, OK, Hiroshi's right: use a seperately-generated
filename
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Tom Lane writes:
> I don't think it's a good idea to have to consult pg_tablespace to find
> out where a table actually is --- I think the pathname (or smgr access
> token as Ross would call it ;-)) ought to be determinable from just the
> pg_class entry.
That's why I suggested the table space oid. That would be readily
available from pg_class.
> Tablespaces can have logical names stored in pg_tablespace; they just
> can't contribute more than a dozen or so characters to file pathnames
> under the implementation I'm proposing. That doesn't seem too
> unreasonable; the pathname part can be some sort of abbreviated name.
Since the abbreviated name is really only used internally it might as well
be the oid. Otherwise you create a weird functional dependency like the
pg_shadow.usesysid field that's just an extra layer of maintenance.
> this implementation mechanism will support either policy choice ---
> original relname in the filename, or just a numeric ID for the
> filename
But when you look at a file name `12345_accounts_recei' you know neither
* whether the table name was really `accounts_recei' or whether the name
was truncated
* whether the table still has that name, whatever it was
* what table this is at all
So in the aggregate you really know less than nothing. :-)
> > Why not use OID.[SEGMENT.]VERSION for the physical relname (different
> > order possible)?
>
> Doesn't give you a manageable way to split segments across different
> disks.
Okay, so maybe ${base}/TABLESPACEOID/SEGMENT/RELOID.VERSION.
This doesn't need any catalog lookup outside of pg_class, yet it's still
easy to resolve to human-readable names by simple admin tools (SELECT *
FROM pg_foo WHERE oid = xxx). VERSION would be unique within a conceptual
relation, so you could even see how many times the relation was altered in
major ways (kind of).
--
Peter Eisentraut Sernanders v<>g 10:115
peter_e@gmx.net 75262 Uppsala
http://yi.org/peter-e/ Sweden
From pgsql-hackers-owner+M3561@hub.org Sun Jun 18 21:31:03 2000
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From: "Hiroshi Inoue" <Inoue@tpf.co.jp>
To: "Chris Bitmead" <chris@bitmead.com>, "Tom Lane" <tgl@sss.pgh.pa.us>
Cc: "Peter Eisentraut" <peter_e@gmx.net>, <pgsql-hackers@postgresql.org>
Subject: RE: [HACKERS] OK, OK, Hiroshi's right: use a seperately-generated filename
Date: Mon, 19 Jun 2000 09:24:56 +0900
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> -----Original Message-----
> From: pgsql-hackers-owner@hub.org [mailto:pgsql-hackers-owner@hub.org]On
> Behalf Of Chris Bitmead
>
> Tom Lane wrote:
>
> > > Also, you said before that an old relname (after rename) is worse than
> > > none at all. I couldn't agree more.
> >
> > I'm not the one who wants relnames in the physical names ;-). However,
> > this implementation mechanism will support either policy choice ---
> > original relname in the filename, or just a numeric ID for the filename
> > --- and that seems like a good sign to me.
> >
> > > Why not use OID.[SEGMENT.]VERSION for the physical relname (different
> > > order possible)?
>
> Unless VERSION is globally unique like an oid is, having RELNAME.VERSION
> would be a problem if you created a table with the same name as a
> recently renamed table.
>
In my proposal(relname+unique-id),the unique-id is globally unique
and relname is only for dba's convenience. I've said many times that
we should be free from the rule of file naming as far as possible.
I myself don't mind the name of relation files except that they should
be globally unique. I had to propose my opinion for file naming
because people have been so enthusiastic about globally_not_unique
file naming.
Regards.
Hiroshi Inoue
Inoue@tpf.co.jp
From pgsql-hackers-owner+M3523@hub.org Fri Jun 16 22:01:00 2000
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To: Tom Lane <tgl@sss.pgh.pa.us>
CC: pgsql-hackers@postgreSQL.org
Subject: Re: [HACKERS] OK, OK, Hiroshi's right: use a seperately-generated
filename
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Tom Lane wrote:
So
> the thing would act a lot like the original-relname-plus-OID variant
> that's been discussed so far. (Original relname because ALTER TABLE
> RENAME would *not* change the physical file name. But we could
> think about a form of VACUUM that creates a whole new table by
> versioning, and that would presumably bring the physical name back
> in sync with the logical relname.)
At least on UNIX, couldn't you use a hard-link and change the name in
pg_class immediately? Let the brain-dead operating systems use the
vacuum method.
From pgsql-hackers-owner+M3576@hub.org Mon Jun 19 01:58:35 2000
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From: "Hiroshi Inoue" <Inoue@tpf.co.jp>
To: "Peter Eisentraut" <peter_e@gmx.net>
Cc: "PostgreSQL Development" <pgsql-hackers@postgresql.org>,
"Tom Lane" <tgl@sss.pgh.pa.us>
Subject: RE: [HACKERS] OK, OK, Hiroshi's right: use a seperately-generatedfilename
Date: Mon, 19 Jun 2000 13:52:34 +0900
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> -----Original Message-----
> From: pgsql-hackers-owner@hub.org [mailto:pgsql-hackers-owner@hub.org]On
> Behalf Of Peter Eisentraut
>
> Tom Lane writes:
>
> > I don't think it's a good idea to have to consult pg_tablespace to find
> > out where a table actually is --- I think the pathname (or smgr access
> > token as Ross would call it ;-)) ought to be determinable from just the
> > pg_class entry.
>
> That's why I suggested the table space oid. That would be readily
> available from pg_class.
>
It seems to me that the following 1)2) has always been mixed up.
IMHO,they should be distinguished clearly.
1) Where the table is stored
Currently PostgreSQL relies on relname -> filename mapping
rule to access *existent* relations and doesn't have this
information in its database. Our(Tom,Ross,me) proposal is to
keep the information(token) in pg_class and provide a standard
transactional control mechanism for the change of table file
allocation. By doing it we would be able to be free from table
allocation(naming) rule.
Isn't it a kind of thing why we haven't had it from the first ?
2) Where to store the table
Yes,TABLE(DATA)SPACE should encapsulate this concept.
I want the decision about 1) first. Ross has already tried it without
2).
Comments ?
As for 2) every one seems to have each opinion and the discussion
has always been divergent. Please don't discard 1) together.
Regards.
Hiroshi Inoue
Inoue@tpf.co.jp
From pgsql-hackers-owner+M3591@hub.org Mon Jun 19 11:01:19 2000
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From: Zeugswetter Andreas SB <ZeugswetterA@wien.spardat.at>
To: "'Tom Lane'" <tgl@sss.pgh.pa.us>, Peter Eisentraut <peter_e@gmx.net>
Cc: pgsql-hackers@postgresql.org
Subject: AW: [HACKERS] OK, OK, Hiroshi's right: use a seperately-generated
filename
Date: Mon, 19 Jun 2000 15:46:22 +0200
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> It's better than *all* segments of tables in one directory, which is
> what you get if the segment number is just a component of a flat file
> name. We have to have a better answer than that for people who need
> to cope with tables bigger than a disk. Perhaps someone can
> think of a
> better answer than subdirectory-per-segment-number, but I think that
> will work well enough; and it doesn't add any complexity for file
> access.
I do not see this connection between a filesystem and a disk ?
Modern systems have the ability to join more than one disk into
one filesystem.
Also if we think about separating large tables into smaller parts
we imho want something where the optimizer has knowledge
what data it finds in what part of the table.
Andreas
From pgsql-hackers-owner+M4680@hub.org Mon Jul 10 11:16:07 2000
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Date: Mon, 10 Jul 2000 10:03:54 -0400
From: Mike Mascari <mascarm@mascari.com>
Organization: Mascari Development Inc
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To: Bruce Momjian <pgman@candle.pha.pa.us>
CC: Tom Lane <tgl@sss.pgh.pa.us>, Philip Warner <pjw@rhyme.com.au>,
Chris Bitmead <chrisb@nimrod.itg.telstra.com.au>,
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Subject: Re: [HACKERS] Re: [GENERAL] PostgreSQL vs. MySQL
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Bruce Momjian wrote:
>
> > And of course the major problem with *that* is how do you get the
> > connection request to arrive at a backend that's been prestarted in
> > the right database? If you don't commit to a database then there's
> > not a whole lot of prestarting that can be done.
> >
> > It occurs to me that this'd get a whole lot more feasible if one
> > postmaster == one database, which is something we *could* do if we
> > implemented schemas. Hiroshi's been arguing that the current hard
> > separation between databases in an installation should be done away
> > with in favor of schemas, and I'm starting to see his point...
>
> This is interesting. You believe schema's would allow a pool of
> backends to connect to any database? That would clearly be a win.
I'm just curious, but did a consensus ever develop on schemas? It
seemed that the schemas/tablespace thread just ran out of steam.
For what its worth, I like the idea of:
1. PostgreSQL installation -> SQL cluster of catalogs
2. PostgreSQL database -> SQL catalog
3. PostgreSQL schema -> SQL schema
This correlates nicely with the current representation of
DATABASE. People can run multiple SQL clusters by running
multiple postmasters on different ports. Today, most people
achieve a logical separation of data by issuing multiple CREATE
DATABASE commands. But under the above, most sites would run with
a single PostgreSQL database (SQL catalog), since:
"Catalogs are named collections of schemas in an SQL-environment"
This would mirror the behavior of Oracle, where most people run
with a single Oracle SID. The logical separation would be
achieved with SCHEMA's a level under the current DATABASE (a.k.a.
catalog). This eliminates the problem of using softlinks and
creating various subdirectories to mirror *logical* parititioning
of data. It also alleviates the problem people currently
encounter when they've built their data model around multiple
DATABASE's but learn later that they need access to more than one
simultaneously. Instead, they'll model their design around
multiple SCHEMA's which exist within a single DATABASE instance.
It seems that the discussion of tablespaces shouldn't be mixed
with SCHEMA's except to note that a DATABASE (catalog) should
have a default TABLESPACE whose path matches the current one:
../pgsql/data/base/<mydatabase>
Later, users might be able to create a hierarchy of default
TABLESPACE's where the location of the object is found with logic
like:
1. Is there a object-specified tablespace?
(ex: CREATE TABLE payroll IN TABLESPACE...)
2. Is there a user-specified default tablespace?
(ex: CREATE USER mike DEFAULT TABLESPACE...)
2. Is there a schema-specified default tablespace?
(ex: CREATE SCHEMA accounting DEFAULT TABLESPACE..)
3. Use the catalog-default tablespace
(ex: CREATE DATABASE postgres DEFAULT LOCATION '/home/pgsql')
with the last example creating the system tablespace,
'system_tablespace', with '/home/pgsql' as the location.
Anyways, it seems a consensus should be developed on the whole
Cluster/Catalog/Schema scenario.
Mike Mascari
From Albert.Langer@Directory-Designs.org Sun Apr 15 12:57:07 2001
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From: "Albert Langer" <Albert.Langer@Directory-Designs.org>
To: "'Bruce Momjian'" <pgman@candle.pha.pa.us>,
"'Hiroshi Inoue'" <Inoue@tpf.co.jp>,
"'Ross J. Reedstrom'" <reedstrm@wallace.ece.rice.edu>,
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"'Vadim Mikheev'" <vmikheev@SECTORBASE.COM>
Subject: Tablespaces - checkout SAP DB
Date: Mon, 16 Apr 2001 02:56:04 +1000
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Hi everyone,
Sorry about the long To list - this is to everyone I noticed commenting in:
http://www.postgresql.org/docs/pgsql/doc/TODO.detail/tablespaces
I strongly recommend checkout of approach used in SAP DB:
http://www.sap.com/solutions/technology/sapdb/sap_db_documentation.htm
Their glossy 2 page brochure emphasizes the way they handle
tablespaces as strongest point for ease of administration:
http://www.sap.com/solutions/technology/sapdb/pdf/50033321.pdf
Directory distribution explained in:
http://www.sap.com/solutions/technology/sapdb/pdf/directorydistrib_72eng.pdf
Architecture and tablespace/devspace concepts explained in:
http://www.sap.com/solutions/technology/sapdb/pdf/dbmgui_73eng.pdf
(721K)
A good short overview can be obtained from the Glossary:
http://www.sap.com/solutions/technology/sapdb/sap_db_glossary.htm
(not .pdf - ordinary html)
vvvvvvv
data devspace
The user data (tables, indexes) and the SQL catalog are stored in the data
devspaces. A table or an index needs one page (minimum); a table can use all
the data devspaces that is the whole database (maximum). A table increases
or decreases in size automatically without administrative intervention.
As a rule, a database internal striping algorithm distributes the data
belonging to a table evenly across all the data devspaces. An assignment of
tables to data devspaces is not possible nor is it necessary.
When installing the database instance you can configure one or more data
devspaces and while the database is running you can also add new data
devspaces. The disk storage space defined by all the data devspaces is the
total size of the database.
devspace
This term denotes a physical disk or part of a physical disk. This can be a
raw device or a file.
log devspace
What is recorded in a log devspace is all the changes in the contents of the
database, to enable the contents to be recovered or restored after hardware
faults. The complete log can consist of a number of devspaces. You can
define the number of log devspaces required when installing the database
instance and can add new log devspaces even while the database is operating.
To ensure that the data on the database is kept safe, you have the option of
mirroring the log devspace(s) (set parameter LOG_MODE to DUAL).
In log backups the contents of the log devspace(s) is copied to a file and
the space originally occupied by it is released for log data. The backup
files are numbered by the system in sequence. The selected size of the
archive log devspace should therefore be sufficient for all the changes
occurring between two backups to be recorded there.
serverdb
A Serverdb consists of the system devspace, one or more log devspaces, and
one or more data devspaces.
For security and performance reasons, each devspace type should be kept on a
different disk. The log devspaces of a serverdb can also be mirrored to
obtain a higher degree of availability. The disks used should present
uniform performance data (especially access speeds) because this is the only
way that equal usage of the devspaces can be achieved. If necessary, a
database instance can be expanded by additional data devspaces while the
database is running.
The devspace usage level of a database instance is therefore a critical
parameter of database operation and must be monitored. If the data devspaces
become full, database operation stops. Further data devspaces can be defined
in this state to allow database operation to continue.
system devspace
The restart information and the mapping of the logical page numbers to
physical page addresses are administered in the system devspace. The size of
the system devspace therefore depends directly on the database size and is
determined by the database kernel.
^^^^^^^^^^^^^^^^^
Concept of just flexibly assigning space to databases,
with only two types of space that should be kept on
different spindlesets, plus the ability to add space
*while running* is what justifies their claim to much
easier admin than Oracle.
Many Postgresql sites run with far too few spindles anyway
and don't have DBAs with a clue what to do with tablespaces.
Now that SAP DB is also open source, making it easy for them
could be critically important.
I'm not even subscribed to pgsql-hacker and don't understand
the internals enough to have any view on whether it's possible
or how.
But if it is possible to present similar *concepts* to DBAs
from the "outside", with whatever actually goes on internally,
that would be really *great*.
Once the internals are done, others could more easily add
admin tools and documentation comparable to SAP DB. Given
the overwhelming advantages of PostgreSQL from all other
points of view, this could be critically important.
I was surprised to find no discussion of comparisons with
SAP DB and what could be learned from it's source release
in a quick search of the web site and mailing lists.
Seeya, Albert
From pgsql-general-owner+M14288@postgresql.org Mon Aug 27 10:31:19 2001
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Date: Mon, 27 Aug 2001 23:38:15 +1000
From: Martijn van Oosterhout <kleptog@svana.org>
To: newsreader@mediaone.net
cc: Jeff Davis <list-pgsql-general@dynworks.com>, pgsql-general@postgresql.org
Subject: Re: [GENERAL] raw partition
Message-ID: <20010827233815.B32309@svana.org>
Reply-To: Martijn van Oosterhout <kleptog@svana.org>
References: <20010826125450.A11535@dragon.universe> <0GIP004VTV1MTO@mta7.pltn13.pbi.net> <20010827091141.A3208@dragon.universe>
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On Mon, Aug 27, 2001 at 09:11:41AM -0400, newsreader@mediaone.net wrote:
> On Mon, Aug 27, 2001 at 12:46:16AM -0700, Jeff Davis wrote:
> > On Sunday 26 August 2001 09:54 am, you wrote:
> >
> > Obviously, if done properly, it couldn't hurt. However, is it really worth
> > the extra trouble to set it up, and more so, to debug an extra form that disk
>
> I think it's only a matter of getting rid
> of file system layer.
But that won't work. Postgres currently stores each table in its own file.
Thus, to implement raw access postgres would have to implement it's own
filesystem within the raw partition.
By using the filesystems built into the OS, it can take advantage of
filesystem smarts already there. No to mention people just being able to use
normal system commands to view what's there e.g. symlinks to relocate
tables. I beleive that filesystem technology within the OS will advance much
faster than anything the postgres developers could come up with.
For example, by running your database on an ext3 partition, all file
metadata is automatically journalled, with no additional effort from the
postgres developers. You could even choose to journal all database access
(though I have no idea how that interacts with WAL).
> > marginal utility for integrated functionality? Consider this: should postgres
> > be it's own OS; bootable and everything (get rid of all that OS overhead)? I
>
> file system overhead is all, I think.
> The only thing I am sure about is that
> whether pg (and developers) will have to be
> aware of the disk technology since it is
> evolving continuosly. Or is there another
> layer provided by the OS: a layer
> between physical disk and the filesystem?
> That layer will have to understand UDMA technology,
> SCSI technology? I have no idea.
Well, a raw partition provided by the OS would hide such details. However,
postgres would have to make assumptions about what kind of access patterns
are optimal. The kernel is in a much better position to make such decisions
about resource usage. Which is precisly why we have OS's in the first place.
> > oracle allows this behaviour you speak of, but I have never used it. Does
> > someone have experience (or benchmarks or whatever) with oracle's
> > implementation?
>
> I have never used an oracle
I beleive (someone correct me if I'm wrong) that even when used on a
filesystem, oracle still places all it's tables in a single file i.e. it has
a filesystem layer builtin. I think that's why it's a clear win for oracle
because you *are* actually removing a layer.
IMHO it's something postgres should stay well away from.
--
Martijn van Oosterhout <kleptog@svana.org>
http://svana.org/kleptog/
> It would be nice if someone came up with a certification system that
> actually separated those who can barely regurgitate what they crammed over
> the last few weeks from those who command secret ninja networking powers.
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