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Remove unused TODO.detail functions.

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Bruce Momjian 2001-01-29 17:57:26 +00:00
parent da0e6bfeaf
commit 99f964fcc6
4 changed files with 5 additions and 1201 deletions
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10
doc/TODO
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@ -56,7 +56,7 @@ ENHANCEMENTS
URGENT
* -Add OUTER joins, left and right[outer] (Tom, Thomas)
* -Add OUTER joins, left and right (Tom, Thomas)
* -Allow long tuples by chaining or auto-storing outside db (TOAST) (Jan)
* -Fix memory leak for expressions (Tom)
* Add replication of distributed databases [replication]
@ -95,7 +95,7 @@ TYPES
o -Allow large object vacuuming
o -Tables that start with xinv confused to be large objects
* Add IPv6 capability to INET/CIDR types
* -Fix improper masking of some inet/cidr types [cidr]
* -Fix improper masking of some inet/cidr types
* Add conversion function from text to inet
* Make a separate SERIAL type?
* Store binary-compatible type information in the system
@ -224,7 +224,7 @@ EXOTIC FEATURES
* Add the concept of dataspaces/tablespaces [tablespaces]
* Allow queries across multiple databases
* Allow nested transactions (Vadim)
* Allow [INSERT/UPDATE] ... RETURNING new.col or old.col (Philip)
* Allow INSERT/UPDATE ... RETURNING new.col or old.col (Philip)
* SQL*Net listener that makes PostgreSQL appear as an Oracle database
to clients
* Incremental backups
@ -242,13 +242,13 @@ MISCELLANEOUS
* Allow cursors to be DECLAREd/OPENed/CLOSEed outside transactions
* Allow DELETE WHERE CURRENT OF cursor
* -Transaction log, so re-do log can be on a separate disk by
with after-row images (Vadim) [logging]
with after-row images (Vadim)
* Populate backend status area and write program to dump status data
* Make oid use unsigned int more reliably, pg_atoi()
* Put sort files in their own directory
* Allow autocommit so always in a transaction block
* Show location of syntax error in query [yacc]
* -Redesign the function call interface to handle NULLs better[function] (Tom)
* -Redesign the function call interface to handle NULLs better (Tom)
* Missing optimizer selectivities for date, r-tree, etc. [optimizer]
* Overhaul bufmgr/lockmgr/transaction manager
* -redesign UNION structures to have separarate target lists

519
doc/TODO.detail/function
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@ -1,519 +0,0 @@
From owner-pgsql-hackers@hub.org Wed Sep 22 20:31:02 1999
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To: pgsql-hackers@postgreSQL.org
Subject: [HACKERS] Progress report: buffer refcount bugs and SQL functions
Date: Wed, 22 Sep 1999 20:05:39 -0400
Message-ID: <6408.938045139@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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Precedence: bulk
Status: RO
I have been finding a lot of interesting stuff while looking into
the buffer reference count/leakage issue.
It turns out that there were two specific things that were camouflaging
the existence of bugs in this area:
1. The BufferLeakCheck routine that's run at transaction commit was
only looking for nonzero PrivateRefCount to indicate a missing unpin.
It failed to notice nonzero LastRefCount --- which meant that an
error in refcount save/restore usage could leave a buffer pinned,
and BufferLeakCheck wouldn't notice.
2. The BufferIsValid macro, which you'd think just checks whether
it's handed a valid buffer identifier or not, actually did more:
it only returned true if the buffer ID was valid *and* the buffer
had positive PrivateRefCount. That meant that the common pattern
if (BufferIsValid(buf))
ReleaseBuffer(buf);
wouldn't complain if it were handed a valid but already unpinned buffer.
And that behavior masks bugs that result in buffers being unpinned too
early. For example, consider a sequence like
1. LockBuffer (buffer now has refcount 1). Store reference to
a tuple on that buffer page in a tuple table slot.
2. Copy buffer reference to a second tuple-table slot, but forget to
increment buffer's refcount.
3. Release second tuple table slot. Buffer refcount drops to 0,
so it's unpinned.
4. Release original tuple slot. Because of BufferIsValid behavior,
no assert happens here; in fact nothing at all happens.
This is, of course, buggy code: during the interval from 3 to 4 you
still have an apparently valid tuple reference in the original slot,
which someone might try to use; but the buffer it points to is unpinned
and could be replaced at any time by another backend.
In short, we had errors that would mask both missing-pin bugs and
missing-unpin bugs. And naturally there were a few such bugs lurking
behind them...
3. The buffer refcount save/restore stuff, which I had suspected
was useless, is not only useless but also buggy. The reason it's
buggy is that it only works if used in a nested fashion. You could
save state A, pin some buffers, save state B, pin some more
buffers, restore state B (thereby unpinning what you pinned since
the save), and finally restore state A (unpinning the earlier stuff).
What you could not do is save state A, pin, save B, pin more, then
restore state A --- that might unpin some of A's buffers, or some
of B's buffers, or some unforeseen combination thereof. If you
restore A and then restore B, you do not necessarily return to a zero-
pins state, either. And it turns out the actual usage pattern was a
nearly random sequence of saves and restores, compounded by a failure to
do all of the restores reliably (which was masked by the oversight in
BufferLeakCheck).
What I have done so far is to rip out the buffer refcount save/restore
support (including LastRefCount), change BufferIsValid to a simple
validity check (so that you get an assert if you unpin something that
was pinned), change ExecStoreTuple so that it increments the refcount
when it is handed a buffer reference (for symmetry with ExecClearTuple's
decrement of the refcount), and fix about a dozen bugs exposed by these
changes.
I am still getting Buffer Leak notices in the "misc" regression test,
specifically in the queries that invoke more than one SQL function.
What I find there is that SQL functions are not always run to
completion. Apparently, when a function can return multiple tuples,
it won't necessarily be asked to produce them all. And when it isn't,
postquel_end() isn't invoked for the function's current query, so its
tuple table isn't cleared, so we have dangling refcounts if any of the
tuples involved are in disk buffers.
It may be that the save/restore code was a misguided attempt to fix
this problem. I can't tell. But I think what we really need to do is
find some way of ensuring that Postquel function execution contexts
always get shut down by the end of the query, so that they don't leak
resources.
I suppose a straightforward approach would be to keep a list of open
function contexts somewhere (attached to the outer execution context,
perhaps), and clean them up at outer-plan shutdown.
What I am wondering, though, is whether this addition is actually
necessary, or is it a bug that the functions aren't run to completion
in the first place? I don't really understand the semantics of this
"nested dot notation". I suppose it is a Berkeleyism; I can't find
anything about it in the SQL92 document. The test cases shown in the
misc regress test seem peculiar, not to say wrong. For example:
regression=> SELECT p.hobbies.equipment.name, p.hobbies.name, p.name FROM person p;
name |name |name
-------------+-----------+-----
advil |posthacking|mike
peet's coffee|basketball |joe
hightops |basketball |sally
(3 rows)
which doesn't appear to agree with the contents of the underlying
relations:
regression=> SELECT * FROM hobbies_r;
name |person
-----------+------
posthacking|mike
posthacking|jeff
basketball |joe
basketball |sally
skywalking |
(5 rows)
regression=> SELECT * FROM equipment_r;
name |hobby
-------------+-----------
advil |posthacking
peet's coffee|posthacking
hightops |basketball
guts |skywalking
(4 rows)
I'd have expected an output along the lines of
advil |posthacking|mike
peet's coffee|posthacking|mike
hightops |basketball |joe
hightops |basketball |sally
Is the regression test's expected output wrong, or am I misunderstanding
what this query is supposed to do? Is there any documentation anywhere
about how SQL functions returning multiple tuples are supposed to
behave?
regards, tom lane
************
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To: Andreas Zeugswetter <andreas.zeugswetter@telecom.at>
cc: hackers@postgreSQL.org
Subject: Re: [HACKERS] Progress report: buffer refcount bugs and SQL functions
In-reply-to: Your message of Thu, 23 Sep 1999 10:07:24 +0200
<37E9DFBC.5C0978F@telecom.at>
Date: Thu, 23 Sep 1999 10:51:10 -0400
Message-ID: <14209.938098270@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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Andreas Zeugswetter <andreas.zeugswetter@telecom.at> writes:
> That is what I use it for. I have never used it with a
> returns setof function, but reading the comments in the regression test,
> -- mike needs advil and peet's coffee,
> -- joe and sally need hightops, and
> -- everyone else is fine.
> it looks like the results you expected are correct, and currently the
> wrong result is given.
Yes, I have concluded the same (and partially fixed it, per my previous
message).
> Those that don't have a hobbie should return name|NULL|NULL. A hobbie
> that does'nt need equipment name|hobbie|NULL.
That's a good point. Currently (both with and without my uncommitted
fix) you get *no* rows out from ExecTargetList if there are any Iters
that return empty result sets. It might be more reasonable to treat an
empty result set as if it were NULL, which would give the behavior you
suggest.
This would be an easy change to my current patch, and I'm prepared to
make it before committing what I have, if people agree that that's a
more reasonable definition. Comments?
regards, tom lane
************
From owner-pgsql-hackers@hub.org Thu Sep 23 04:31:15 1999
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From: Andreas Zeugswetter <andreas.zeugswetter@telecom.at>
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To: hackers@postgreSQL.org
Subject: Re: [HACKERS] Progress report: buffer refcount bugs and SQL functions
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> Is the regression test's expected output wrong, or am I
> misunderstanding
> what this query is supposed to do? Is there any
> documentation anywhere
> about how SQL functions returning multiple tuples are supposed to
> behave?
They are supposed to behave somewhat like a view.
Not all rows are necessarily fetched.
If used in a context that needs a single row answer,
and the answer has multiple rows it is supposed to
runtime elog. Like in:
select * from tbl where col=funcreturningmultipleresults();
-- this must elog
while this is ok:
select * from tbl where col in (select funcreturningmultipleresults());
But the caller could only fetch the first row if he wanted.
The nested notation is supposed to call the function passing it the tuple
as the first argument. This is what can be used to "fake" a column
onto a table (computed column).
That is what I use it for. I have never used it with a
returns setof function, but reading the comments in the regression test,
-- mike needs advil and peet's coffee,
-- joe and sally need hightops, and
-- everyone else is fine.
it looks like the results you expected are correct, and currently the
wrong result is given.
But I think this query could also elog whithout removing substantial
functionality.
SELECT p.name, p.hobbies.name, p.hobbies.equipment.name FROM person p;
Actually for me it would be intuitive, that this query return one row per
person, but elog on those that have more than one hobbie or a hobbie that
needs more than one equipment. Those that don't have a hobbie should
return name|NULL|NULL. A hobbie that does'nt need equipment name|hobbie|NULL.
Andreas
************
From owner-pgsql-hackers@hub.org Wed Sep 22 22:01:07 1999
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From: wieck@debis.com (Jan Wieck)
Subject: Re: [HACKERS] Progress report: buffer refcount bugs and SQL functions
To: tgl@sss.pgh.pa.us (Tom Lane)
Date: Thu, 23 Sep 1999 03:19:39 +0200 (MET DST)
Cc: pgsql-hackers@postgreSQL.org
Reply-To: wieck@debis.com (Jan Wieck)
In-Reply-To: <6408.938045139@sss.pgh.pa.us> from "Tom Lane" at Sep 22, 99 08:05:39 pm
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Tom Lane wrote:
> [...]
>
> What I am wondering, though, is whether this addition is actually
> necessary, or is it a bug that the functions aren't run to completion
> in the first place? I don't really understand the semantics of this
> "nested dot notation". I suppose it is a Berkeleyism; I can't find
> anything about it in the SQL92 document. The test cases shown in the
> misc regress test seem peculiar, not to say wrong. For example:
>
> [...]
>
> Is the regression test's expected output wrong, or am I misunderstanding
> what this query is supposed to do? Is there any documentation anywhere
> about how SQL functions returning multiple tuples are supposed to
> behave?
I've said some time (maybe too long) ago, that SQL functions
returning tuple sets are broken in general. This nested dot
notation (which I think is an artefact from the postquel
querylanguage) is implemented via set functions.
Set functions have total different semantics from all other
functions. First they don't really return a tuple set as
someone might think - all that screwed up code instead
simulates that they return something you could consider a
scan of the last SQL statement in the function. Then, on
each subsequent call inside of the same command, they return
a "tupletable slot" containing the next found tuple (that's
why their Func node is mangled up after the first call).
Second they have a targetlist what I think was originally
intended to extract attributes out of the tuples returned
when the above scan is asked to get the next tuple. But as I
read the code it invokes the function again and this might
cause the resource leakage you see.
Third, all this seems to never have been implemented
(thought?) to the end. A targetlist doesn't make sense at
this place because it could at max contain a single attribute
- so a single attno would have the same power. And if set
functions could appear in the rangetable (FROM clause), than
they would be treated as that and regular Var nodes in the
query would do it.
I think you shouldn't really care for that regression test
and maybe we should disable set functions until we really
implement stored procedures returning sets in the rangetable.
Set functions where planned by Stonebraker's team as
something that today is called stored procedures. But AFAIK
they never reached the useful state because even in Postgres
4.2 you haven't been able to get more than one attribute out
of a set function. It was a feature of the postquel
querylanguage that you could get one attribute from a set
function via
RETRIEVE (attributename(setfuncname()))
While working on the constraint triggers I've came across
another regression test (triggers :-) that's errorneous too.
The funny_dup17 trigger proc executes an INSERT into the same
relation where it get fired for by a previous INSERT. And it
stops this recursion only if it reaches a nesting level of
17, which could only occur if it is fired DURING the
execution of it's own SPI_exec(). After Vadim quouted some
SQL92 definitions about when constraint checks and triggers
are to be executed, I decided to fire regular triggers at the
end of a query too. Thus, there is absolutely no nesting
possible for AFTER triggers resulting in an endless loop.
Jan
--
#======================================================================#
# It's easier to get forgiveness for being wrong than for being right. #
# Let's break this rule - forgive me. #
#========================================= wieck@debis.com (Jan Wieck) #
************
From owner-pgsql-hackers@hub.org Thu Sep 23 11:01:06 1999
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To: wieck@debis.com (Jan Wieck)
cc: pgsql-hackers@postgreSQL.org
Subject: Re: [HACKERS] Progress report: buffer refcount bugs and SQL functions
In-reply-to: Your message of Thu, 23 Sep 1999 03:19:39 +0200 (MET DST)
<m11TxXw-0003kLC@orion.SAPserv.Hamburg.dsh.de>
Date: Thu, 23 Sep 1999 10:18:01 -0400
Message-ID: <13251.938096281@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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wieck@debis.com (Jan Wieck) writes:
> Tom Lane wrote:
>> What I am wondering, though, is whether this addition is actually
>> necessary, or is it a bug that the functions aren't run to completion
>> in the first place?
> I've said some time (maybe too long) ago, that SQL functions
> returning tuple sets are broken in general.
Indeed they are. Try this on for size (using the regression database):
SELECT p.name, p.hobbies.equipment.name FROM person p;
SELECT p.hobbies.equipment.name, p.name FROM person p;
You get different result sets!?
The problem in this example is that ExecTargetList returns the isDone
flag from the last targetlist entry, regardless of whether there are
incomplete iterations in previous entries. More generally, the buffer
leak problem that I started with only occurs if some Iter nodes are not
run to completion --- but execQual.c has no mechanism to make sure that
they have all reached completion simultaneously.
What we really need to make functions-returning-sets work properly is
an implementation somewhat like aggregate functions. We need to make
a list of all the Iter nodes present in a targetlist and cycle through
the values returned by each in a methodical fashion (run the rightmost
through its full cycle, then advance the next-to-rightmost one value,
run the rightmost through its cycle again, etc etc). Also there needs
to be an understanding of the hierarchy when an Iter appears in the
arguments of another Iter's function. (You cycle the upper one for
*each* set of arguments created by cycling its sub-Iters.)
I am not particularly interested in working on this feature right now,
since AFAIK it's a Berkeleyism not found in SQL92. What I've done
is to hack ExecTargetList so that it behaves semi-sanely when there's
more than one Iter at the top level of the target list --- it still
doesn't really give the right answer, but at least it will keep
generating tuples until all the Iters are done at the same time.
It happens that that's enough to give correct answers for the examples
shown in the misc regress test. Even when it fails to generate all
the possible combinations, there will be no buffer leaks.
So, I'm going to declare victory and go home ;-). We ought to add a
TODO item along the lines of
* Functions returning sets don't really work right
in hopes that someone will feel like tackling this someday.
regards, tom lane
************

285
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@ -1,285 +0,0 @@
From owner-pgsql-hackers@hub.org Fri Nov 13 13:24:37 1998
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From: jwieck@debis.com (Jan Wieck)
Subject: [HACKERS] shmem limits and redolog
To: pgsql-hackers@postgreSQL.org (PostgreSQL HACKERS)
Date: Fri, 13 Nov 1998 19:46:20 +0100 (MET)
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Hi,
I'm currently hacking around on a solution for logging all
database operations at query level that can recover a crashed
database from the last successful backup by redoing all the
commands.
Well, I wanted it to be as flexible as can. So I decided to
make it per database configurable. One could say which
databases are logged and if a database is, if it is logged
sync or async (in sync mode, every COMMIT forces an fsync of
the actual logfile and controlfiles).
To make async mode as fast as can, I'm using a shared memory
of 32K per database (not per backend) that is used as a wrap
around buffer from the backends to place their query
information. So the log writer can fall a little behind if
there are many backends doing different things that don't
lock each other.
Now I'm a little in doubt about the shared memory limits
reported. Was it a good decision to use shared memory? Am I
better off using socket's?
The bad thing in what I have up to now (it's far from
complete) is, that even if a database isn't currently logged,
a redolog writer is started and creates the 32K shmem segment
(plus a semaphore set with 5 semaphores). This is because I
plan to create commands like
ALTER DATABASE LOG MODE=ASYNC LOGDIR='/somewhere/dbname';
and the like that can be used at runtime (while more than one
backend is connected to the database) to turn logging on/off,
switch to/from backup mode (all other activity is stopped)
etc.
So every 32 databases will require another megabyte of shared
memory. The logging master controls which databases have
activity and kills redolog writers after some time of
inactivity, and the shmem is freed then. But it can hurt if
someone really has many many databases that are all used at
the same time.
What do the others say?
Jan
--
#======================================================================#
# It's easier to get forgiveness for being wrong than for being right. #
# Let's break this rule - forgive me. #
#======================================== jwieck@debis.com (Jan Wieck) #
From owner-pgsql-hackers@hub.org Wed Dec 16 15:46:41 1998
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From: jwieck@debis.com (Jan Wieck)
Subject: Re: [HACKERS] redolog - for discussion
To: vadim@krs.ru (Vadim Mikheev)
Date: Wed, 16 Dec 1998 21:07:00 +0100 (MET)
Cc: jwieck@debis.com, pgsql-hackers@postgreSQL.org
Reply-To: jwieck@debis.com (Jan Wieck)
In-Reply-To: <3677B71D.C67462B3@krs.ru> from "Vadim Mikheev" at Dec 16, 98 08:35:25 pm
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Vadim wrote:
>
> Jan Wieck wrote:
> >
> > RECOVER DATABASE {ALL | UNTIL 'datetime' | RESET};
> >
> ...
> >
> > For the others, the backend starts the recovery program
> > which reads the redolog files, establishes database
> > connections as required and reruns all the commands in
> ^^^^^^^^^^^^^^^^^^^^^^^^^^
> > them. If a required logfile isn't found, it tells the
> ^^^^^
>
> I foresee problems with using _commands_ logging for
> recovery/replication -:((
>
> Let's consider two concurrent updates in READ COMMITTED mode:
>
> update test set x = 2 where y = 1;
>
> and
>
> update test set x = 3 where y = 1;
>
> The result of both committed transaction will be x = 2
> if the 1st transaction updated row _after_ 2nd transaction
> and x = 3 if the 2nd transaction gets row after 1st one.
> Order of updates is not defined by order in which commands
> begun and so order in which commands should be rerun
> will be unknown...
Yepp, the order in which commands begun is absolutely not of
interest. Locking could already delay the execution of one
command until another one started later has finished and
released the lock. It's a classic race condition.
Thus, my plan was to log the queries just before the call to
CommitTransactionCommand() in tcop. This has the advantage,
that queries which bail out with errors don't get into the
log at all and must not get rerun. And I can set a static
flag to false before starting the command, which is set to
true in the buffer manager when a buffer is written (marked
dirty), so filtering out queries that do no updates at all is
easy.
Unfortunately query level logging get's hit by the current
implementation of sequence numbers. If a query that get's
aborted somewhere in the middle (maybe by a trigger) called
nextval() for rows processed earlier, the sequence number
isn't advanced at recovery time, because the query is
suppressed at all. And sequences aren't locked, so for
concurrently running queries getting numbers from the same
sequence, the results aren't reproduceable. If some
application selects a value resulting from a sequence and
uses that later in another query, how could the redolog know
that this has changed? It's a Const in the query logged, and
all that corrupts the whole thing.
All that is painful and I don't see another solution yet than
to hook into nextval(), log out the numbers generated in
normal operation and getting back the same numbers in redo
mode.
The whole thing gets more and more complicated :-(
Jan
--
#======================================================================#
# It's easier to get forgiveness for being wrong than for being right. #
# Let's break this rule - forgive me. #
#======================================== jwieck@debis.com (Jan Wieck) #
From owner-pgsql-hackers@hub.org Wed Jun 16 09:29:31 1999
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From: Vadim Mikheev <vadim@krs.ru>
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To: PostgreSQL Developers List <hackers@postgreSQL.org>
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To have them I need to add tuple id (6 bytes) to heap tuple
header. Are there objections? Though it's not good to increase
tuple header size, subj is, imho, very nice feature...
Implementation is , hm, "easy":
- heap_insert/heap_delete/heap_replace/heap_mark4update will
remember updated tid (and current command id) in relation cache
and store previously updated tid (remembered in relation cache)
in additional heap header tid;
- lmgr will remember command id when lock was acquired;
- for a savepoint we will just store command id when
the savepoint was setted;
- when going to sleep due to concurrent the-same-row update,
backend will store MyProc and tuple id in shmem hash table.
When rolling back to a savepoint, backend will:
- release locks acquired after savepoint;
- for a relation updated after savepoint, get last updated tid
from relation cache, walk through relation, set
HEAP_XMIN_INVALID/HEAP_XMAX_INVALID in all tuples updated
after savepoint and wake up concurrent writers blocked
on these tuples (using shmem hash table mentioned above).
The last feature (waking up of concurrent writers) is most hard
part to implement. AFAIK, Oracle 7.3 was not able to do it.
Can someone comment is this feature implemented in Oracle 8.X,
other DBMSes?
Now about implicit savepoints. Backend will place them before
user statements execution. In the case of failure, transaction
state will be rolled back to the one before execution of query.
As side-effect, this means that we'll get rid of complaints
about entire transaction abort in the case of mistyping
causing abort due to parser errors...
Comments?
Vadim

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From lockhart@alumni.caltech.edu Thu Jan 7 13:31:08 1999
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From: "Thomas G. Lockhart" <lockhart@alumni.caltech.edu>
Organization: Caltech/JPL
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To: Bruce Momjian <maillist@candle.pha.pa.us>
CC: Postgres Hackers List <hackers@postgresql.org>
Subject: Outer Joins (and need CASE help)
References: <199901071747.MAA07054@candle.pha.pa.us>
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Status: RO
> Thomas, do you need help on outer joins?
Yes. I'm going slowly partly because I get distracted with other
Postgres stuff like docs, and partly because I don't understand all of
the pieces I'm working with.
I've identified the place in the MergeJoin code where the null filling
for outer joins needs to happen, and have the "merge walk" code done.
But I don't have the supporting code which actually would know how to
null-fill a result tuple from the left or right. I thought you might be
interested in that?
I've done some work in the parser, and can now do things like:
postgres=> select * from t1 join t2 using (i);
NOTICE: JOIN not yet implemented
i|j|i|k
-+-+-+-
1|2|1|3
(1 row)
But this is just an inner join, and the result isn't quite right since
the second "i" column should probably be omitted. At the moment I
transform it from the syntax above into existing parse nodes, and
everything from there on works.
I don't yet pass an explicit join node into the planner/optimizer, and
that will be the hardest part I assume. Perhaps we can work on that
together.
So, what I'll try to do (soon, in the next few days?) is put in
#ifdef ENABLE_OUTER_JOINS
conditional code into the parser area (already there for the executor)
and commit everything to the development tree. Does that sound OK?
Oh, and if anyone is looking for something to do, I've got a couple of
CASE statements in the case.sql regression test which are commented out
because they crash the backend. They involve references to multiple
tables within a single result column, and in other contexts that
construct works. It would be great if someone had time to track it
down...
- Tom
From lockhart@alumni.caltech.edu Mon Feb 22 02:01:13 1999
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From: "Thomas G. Lockhart" <lockhart@alumni.caltech.edu>
Organization: Caltech/JPL
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To: Bruce Momjian <maillist@candle.pha.pa.us>
CC: hackers@postgreSQL.org
Subject: Re: start on outer join
References: <199902220304.WAA10066@candle.pha.pa.us>
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Bruce Momjian wrote:
>
> > Will apply ... some other changes laying a bit of
> > groundwork for outer joins so you can start on the planner/optimizer
> > parts :)
> Those will be a synch now that I understand the optimizer. In fact, I
> think it all will happen in the executor.
I've modified executor/nodeMergeJoin.c to walk a left/right/both outer
join, but didn't fill in the part which actually creates the result
tuple (which will be the current left- or right-side tuple plus nulls
for filler). I hope this is up your alley :)
So far, I'm not certain what to pass to the planner. The syntax leads me
to pass a select structure from gram.y with a "JoinExpr" structure in
the "fromClause" list. I need to expand that with a combination of
column names and qualifications, but at the time I see the JoinExpr I
don't have access to the top query structure itself. So I may just keep
a modestly transformed JoinExpr to expand later or to pass to the
planner.
btw, the EXCEPT/INTERSECT stuff from Stefan has some ugliness in gram.y
which needs to be fixed (the shift/reduce conflict is not acceptable for
our release version) and some of that code clearly needs to move to
analyze.c or some other module.
- Tom
From maillist Wed Feb 24 05:27:08 1999
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From: Bruce Momjian <maillist>
Message-Id: <199902241027.FAA09648@candle.pha.pa.us>
Subject: Re: [HACKERS] OUTER joins
In-Reply-To: <199902240953.EAA08561@candle.pha.pa.us> from Bruce Momjian at "Feb 24, 1999 4:53:21 am"
To: maillist@candle.pha.pa.us (Bruce Momjian)
Date: Wed, 24 Feb 1999 05:27:07 -0500 (EST)
Cc: lockhart@alumni.caltech.edu, hackers@postgreSQL.org
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>
> How do you propose doing outer joins in non-mergejoin situations?
> Mergejoins can only be used currently in equal joins.
Is your solution going to be to make sure the OUTER table is always a
MergeJoin, or on the outside of a join loop? That could work.
That could get tricky if the table is joined to _two_ other tables.
With the cleaned-up optimizer, we can disable non-merge joins in certain
circumstances, and prevent OUTER tables from being inner in the others.
Is that the plan?
--
Bruce Momjian | http://www.op.net/~candle
maillist@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 lockhart@alumni.caltech.edu Mon Mar 1 13:01:08 1999
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From: "Thomas G. Lockhart" <lockhart@alumni.caltech.edu>
Organization: Caltech/JPL
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To: Bruce Momjian <maillist@candle.pha.pa.us>
CC: PostgreSQL-development <hackers@postgreSQL.org>
Subject: Re: OUTER joins
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(back from a short vacation...)
> How do you propose doing outer joins in non-mergejoin situations?
> Mergejoins can only be used currently in equal joins.
Hadn't thought about it, other than figuring that implementing the
equi-join first was a good start. There is a class of outer join syntax
(the USING clause) which is implicitly an equi-join...
- Tom
From lockhart@alumni.caltech.edu Mon Mar 8 21:55:02 1999
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Organization: Caltech/JPL
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To: Bruce Momjian <maillist@candle.pha.pa.us>
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Subject: Re: OUTER joins
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> > Hadn't thought about it, other than figuring that implementing the
> > equi-join first was a good start. There is a class of outer join
> > syntax (the USING clause) which is implicitly an equi-join...
> Not that easy. You don't automatically get a mergejoin from an
> equijoin. I will have to force outer's to be either mergejoins, or
> inners of non-merge joins. Can you add code to non-merge joins in the
> executor to throw out a null row if it does not find an inner match
> for the outer row, and I will handle the optimizer so it doesn't throw
> a non-conforming plan to the executor.
So far I don't have enough info in the parser to get the
planner/optimizer going. Should we work from the front to the back, or
should I go ahead and look at the non-merge joins? It's painfully
obvious that I don't know anything about the middle parts of this to
proceed without lots more research.
- Tom
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> select *
> from outer tab1, tab2, tab3
> where tab1.col1 = tab2.col1 and
> tab1.col1 = tab3.col1
select *
from t1 left join t2 using (c1)
join t3 on (c1 = t3.c1)
Result:
t1.c1 t1.c2 t2.c2 t3.c1
2 12 NULL 32
t1:
c1 c2
1 11
2 12
3 13
4 14
t2:
c1 c2
1 21
3 23
t3:
c1 c2
2 32
From lockhart@alumni.caltech.edu Wed Mar 10 10:48:54 1999
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Subject: Re: SQL outer
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Just thinking...
If the initial RelOptInfo groupings are derived from the WHERE clause
expressions, how about marking the "outer" property in those expressions
in the parser? istm that is where the parser knows about two tables in
one place, and I'm generating those expressions anyway. We could add a
field(s) to the expression structure, or pass along a slightly different
structure...
- Tom
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> Thomas, what do you think is needed for outer joins?
Bruce and I have talked about it some already:
For outer joins, tables must be combined in a particular order. For
example, a left outer join requires that any entries in the left-side
table which do not have a corresponding entry in the right-side table
be expanded with nulls during the join. The information on the outer
join can't be carried by the rte since the same table can appear twice
in an outer join expression:
select * from t1 left join t2 using (i)
left join t1 on (i = t1.j);
For a query like
select * from t1 left join t2 using (i) where t2.j = 3;
istm that the outer join must be done before the t2 qualification is
applied, and that another ordering may produce the wrong result.
>From what I understand Bruce to say, the planner/optimizer is allowed
to try all kinds of permutations of plans, choosing the one with the
lowest cost. But if the info for the join is carried in a
qualification node, then the planner/optimizer must know that it can't
reorder the query as freely as it does now.
I was thinking of having a new qualification node to carry this info,
and it could be transformed into a mergejoin node which has a couple
of new fields indicating left and/or right outer join behavior.
A hashjoin method may be possible for queries which are structured as
a left outer join; other outer joins will need to use the mergejoin
method. Also, some poorly-qualified outer joins reduce to inner joins,
and perhaps the optimizer can be smart enough to realize this.
- Thomas
--
Thomas Lockhart lockhart@alumni.caltech.edu
South Pasadena, California