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==================================================
Frequently Asked Questions (FAQ) for Postgres95
==================================================
last updated: Sun Aug 11 01:35:34 EDT 1996
current maintainer: Bruce Momjian (maillist@candle.pha.pa.us)
original author: Jolly Chen (jolly@cs.berkeley.edu)
changes in this version (* = modified, + = new):
* 1.8) What documentation is available for Postgres95?
* 3.13) What is the maximum size for a tuple?
* 3.14) I defined indices but my queries don't seem to make use of them. Why?
* 3.37) What is the time-warp feature and how does it relate to vacuum?
+ 3.38) How do I tune the database engine for better performace?
This file is divided approximately as follows:
1.*) General questions
2.*) Installation questions
3.*) Postgres95 Features questions
4.*) Questions about extending Postgres95
5.*) Bugs
Questions answered:
1.1) What is Postgres95?
1.2) What does Postgres95 run on?
1.3) Where can I get Postgres95?
1.4) What's the copyright on Postgres95?
1.5) Support for Postgres95
1.6) Future releases of Postgres95
1.7) Is there a commercial version of Postgres95?
1.9) What version of SQL does Postgres95 use?
1.10) Does Postgres95 work with databases from earlier versions of postgres?
1.11) How many people use Postgres95?
2.1) I get the error "cpp: command not found" when I try to compile
2.2) I get 'yy_flush_buffer undefined' when I try to compile the backend
2.3) initdb doesn't run
2.4) when I start up the postmaster, I get
2.5) The system seems to be confused about commas, decimal points, and
2.6) How do I install postgres95 somewhere other than /usr/local/postgres95?
2.7) The backend compiled successfully, but compiling libpq resulted
in a complaint: "libpq/pqcomm.h" not found when compiling fe-auth.c.
2.8) Where can I find the bug fixes for postgres95?
2.9) I can't apply the patches even though everything looks like it should
work.
2.10) When I run postmaster, I get a Bad System Call core dumped message.
2.11) I get the error message "obj/fmgr.h: No such file or directory"
2.12) When I try to start the postmaster, I get IpcMemoryCreate errors.
2.13) I get the strange make errors right at the beginning:
2.14) I have changed a source file, but a recompile does not see the
3.1) How do I specify a KEY or other constraints on a column?
3.2) Does Postgres95 support nested subqueries?
3.3) How do I define a unique indices?
3.4) I've having a lot of problems with using rules.
3.5) I can't seem to write into the middle of large objects reliably.
3.6) Does postgres95 have a graphical user interface? A report
3.7) How can I write client applications to Postgres95?
3.8) How do I prevent other hosts from accessing my Postgres95
3.9) How do I set up a pg_group?
3.10) What is the exact difference between binary cursors and normal cursors?
3.11) Why doesn't the != operator work?
3.12) What is a R-tree index and what is it used for?
3.13) What is the maximum size for a tuple?
3.14) I defined indices but my queries don't seem to make use of them. Why?
3.15) Are there ODBC drivers for Postgres95?
3.16) How do I use postgres for multi-dimensional indexing (> 2 dimensions)?
3.17) How do I do regular expression searches? case-insensitive
regexp searching?
3.18) I can't access the database as the 'root' user.
3.19) I experienced a server crash during a vacuum. How do I remove the
lock file?
3.20) What is the difference between the various character types?
3.21) In a query, how do I detect if a field is NULL?
3.22) How do I see how the query optimizer is evaluating my query?
3.23) How do I create a serial field?
3.24) How do I create a multi-column index?
3.25) What are the temp_XXX files in my database directory?
3.26) Why are my table files not getting any smaller after a delete?
3.27) Why can't I connect to my database from another machine?
3.28) I get the error 'default index class unsupported' when creating an
index. How do I do it?
3.29) Why does creating an index crash the backend server?
3.30) How do I specify a decimal constant as a float8, or a string as a text?
3.31) How do I find out what indexes or operations are defined in the
database?
3.32) My database is corrupt. I can't do anything. What should I do?
3.33) Createdb, destroydb, createuser,destroyuser don't run. Why?
3.34) Why does 'createuser' return 'unexpected last match in input()'?
3.35) All my servers crash under concurrent table access. Why?
3.36) What tools are available for hooking postgres to Web pages?
3.37) What is the time-warp feature and how does it relate to vacuum?
3.38) How do I tune the database engine for better performace?
4.1) I wrote a user-defined function and when I run it in psql, it
dumps core.
4.2) I get messages of the type NOTICE:PortalHeapMemoryFree: 0x402251d0
4.3) I've written some nifty new types and functions for Postgres95.
4.4) How do I write a C function to return a tuple?
5.1) How do I find out about bug fixes?
5.2) How do I make a bug report?
----------------------------------------------------------------------
Section 1: General Questions
----------------------------------------------------------------------
1.1) What is Postgres95?
Postgres95 is an enhancement of the POSTGRES database
management system, a next-generation DBMS research prototype.
While Postgres95 retains the powerful data model and rich data
types of POSTGRES, it replaces the PostQuel query language with an
extended subset of SQL. Postgres95 is free and the complete
source is available.
Postgres95 development is being performed by a team of Internet
developers who all subscribe to the Postgres95 development mailing
list. The current coordinator is Marc G. Fournier (scrappy@ki.net).
(See below on how to join). This team is now responsible for all
current and future development of Postgres95.
The authors of Postgres95 1.01 were Andrew Yu and Jolly Chen.
Many others have contributed to the porting, testing, debugging and
enhancement of the code. The original Postgres code, from which
Postgres95 is derived, was the effort of many graduate
students, undergraduate students, and staff programmers
working under the direction of Professor Michael Stonebraker
at the University of California, Berkeley.
1.2) What does Postgres95 run on?
The authors have compiled and tested Postgres95 on the following
platforms(some of these compiles require gcc 2.7.0):
- DEC Alpha AXP on OSF/1 2.0
- HP PA-RISC on HP-UX 9.0
- i386 Solaris
- SUN SPARC on Solaris 2.4
- SUN SPARC on SunOS 4.1.3
- DEC MIPS on Ultrix 4.4
- Intel x86 on Linux 1.2 and Linux ELF
- OSs derived from 4.4-lite BSD (NetBSD, FreeBSD)
- IBM on AIX 3.2.5
- BSD/OS 2.0, 2.01 & 2.1
- SGI MIPS on IRIX 5.3
The following ports are bundled with the Postgres95 distribution. The
authors do not have handy access to these platforms but the
ports have been tested by the others.
- Motorola MC68K or Intel x86 on NeXTSTEP 3.2
- Intel x86 on Intel SVR4
1.3) Where can I get Postgres95?
The primary anonymous ftp site for postgres95 is:
ftp://ftp.ki.net/pub/postgres95
A mirror site exists at:
ftp://postgres95.vnet.net/pub/postgres95
1.4) What's the copyright on Postgres95?
Postgres95 is subject to the following COPYRIGHT.
POSTGRES95 Data Base Management System
Copyright (c) 1994-6 Regents of the University of California
Permission to use, copy, modify, and distribute this software and its
documentation for any purpose, without fee, and without a written agreement
is hereby granted, provided that the above copyright notice and this
paragraph and the following two paragraphs appear in all copies.
IN NO EVENT SHALL THE UNIVERSITY OF CALIFORNIA BE LIABLE TO ANY PARTY FOR
DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES, INCLUDING
LOST PROFITS, ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS
DOCUMENTATION, EVEN IF THE UNIVERSITY OF CALIFORNIA HAS BEEN ADVISED OF THE
POSSIBILITY OF SUCH DAMAGE.
THE UNIVERSITY OF CALIFORNIA SPECIFICALLY DISCLAIMS ANY WARRANTIES,
INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
AND FITNESS FOR A PARTICULAR PURPOSE. THE SOFTWARE PROVIDED HEREUNDER IS
ON AN "AS IS" BASIS, AND THE UNIVERSITY OF CALIFORNIA HAS NO OBLIGATIONS TO
PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
1.5) Support for Postgres95
There is no official support for Postgres95 from the original
maintainers or from University of California, Berkeley. It is
maintained through volunteer effort only.
With the generosity of the Jason Wright and others at Vnet,
the postgres95 mailing list now has a new home --
postgres95@postgres95.vnet.net. It is available for
discussion of matters pertaining to Postgres95, including but
not limited to bug reports and fixes. For info on how to
subscribe, send a mail with the lines in the body (not the
subject line):
help
info postgres95
to
majordomo@postgres95.vnet.net
There is also a digest list available. To subscribe to this list,
send email to majordomo@postgres95.vnet.net with a BODY of:
subscribe postgres95-digest
Digests are sent out to members of this list whenever the main list has
received around 30k of messages.
Archives and digests of the new mailing list at Vnet can be found at:
ftp://postgres95.vnet.net/pub/postgres95/archives
ftp://postgres95.vnet.net/pub/postgres95/digests
There is also a developers mailing list available. To subscribe to
this list, send email to pg95-dev-request@ki.net with a BODY of:
subscribe pg95-dev
Additional information about Postgres95 can be found via the
postgres95 WWW home page at:
http://www.ki.net/postgres95
1.6) Future releases of Postgres95
The latest release of postgres95 is version 1.02.
1.7) Is there a commercial version of Postgres95?
Illustra Information Technology (a wholly owned subsidiary of
Informix Software, Inc.) sells an object-relational
DBMS called Illustra that was originally based on postgres.
Illustra has cosmetic similarities to postgres95 but has more
features, is more robust, performs better, and offers real
documentation and support. On the flip side, it costs money.
For more information, contact sales@illustra.com
1.8) What documentation is available for Postgres95?
A user manual, manual pages, and some small test examples
are included in the distribution. The www page contains
pointers to an implementation guide and five papers written
about postgres design concepts and features.
1.9) What version of SQL does Postgres95 use?
Postgres95 supports a subset of SQL-92. It has most of the
important constructs but lacks some of the functionality.
The most visible differences are:
- no support for primary keys or column constraints
- no support for nested subqueries
- no HAVING clause under a GROUP BY
On the other hand, you get to create user-defined types,
functions, inheritance etc. If you're willing to help with
postgres95 coding, eventually we can also add the missing
features listed above.
1.10) Does Postgres95 work with databases from earlier versions of postgres?
Postgres95 v1.02 is compatible with databases created with v1.01.
Those upgrading from 1.0 to 1.02 should read the directions in the
MIGRATION_1.0_TO_1.02 directory.
1.11) How many people use Postgres95?
Since we don't have any licensing or registration scheme, it's
impossible to tell. We do know hundreds copies of postgres95
v1.* have been downloaded, and that there many hundreds of
subscribers to the mailing lists.
----------------------------------------------------------------------
Section 2: Installation Questions
----------------------------------------------------------------------
2.1) I get the error "cpp: command not found" when I try to compile
the backend.
Edit the src/backend/utils/Gen_fmgrtab.sh script to include the path
for the cpp for your particular site.
2.2) I get 'yy_flush_buffer undefined' when I try to compile the backend
Use a more recent version of flex, version 2.5.2. Version 2.5.3
has a known bug.
2.3) initdb doesn't run
* check to see that you have the proper paths set
* check that the 'postgres' user owns all the right files
* ensure that there are files in $PGDATA/files, and that they
are non-empty. If they aren't, then "gmake install" failed for
some reason
2.4) when I start up the postmaster, I get
"FindBackend: could not find a backend to execute..."
"postmaster: could not find backend to execute..."
You probably do not have the right path set up. the 'postgres'
executable needs to be in your path.
2.5) The system seems to be confused about commas, decimal points, and
date formats.
Check your locale configuration. postgres95 uses the locale
settings of the user that ran the postmaster process. Set those
accordingly for your operating environment.
2.6) How do I install postgres95 somewhere other than /usr/local/postgres95?
You need to manually edit the paths in src/Makefile.global to
your site configuration.
2.7) The backend compiled successfully, but compiling libpq resulted
in a complaint: "libpq/pqcomm.h" not found when compiling fe-auth.c.
You've probably installed postgres95 somewhere other than
/usr/local/postgres, but didn't edit the src/Makefile.global
accordingly. See question 2.6.
2.8) Where can I find the bug fixes for postgres95?
The patches should be applied in the order listed. The patch files
can be ftp'ed directly from the directory:
ftp://ftp.ki.net/pub/postgres95
2.9) I can't apply the patches even though everything looks like it should
work.
If you cut and paste directly off your web browser, tabs and
whitespaces may not be preserved properly. Use the 'save as file'
option from your web browser instead.
2.10) When I run postmaster, I get a Bad System Call core dumped message.
It could be a variety of problems, but first check to see that you
have system V extensions installed on your kernel. Postgres95
requires kernel support for shared memory.
2.11) I get the error message "obj/fmgr.h: No such file or directory"
This indicates that you did not generate the file fmgr.h
properly. Something failed in the running of the
src/backend/utils/Gen_fmgrtab.sh script. Check to see the
paths used in that script is appropriate to your system.
2.12) When I try to start the postmaster, I get IpcMemoryCreate errors.
You either do not have shared memory configured properly in kernel
or you need to enlarge the shared memory available in the kernel.
The exact amount you need depends on your architecture and how
many buffers you configure postmaster to run with. For most
systems, with default buffer sizes, you need a minimum of ~760K.
2.13) I get the strange make errors right at the beginning:
warning: NUL character seen; rest of line ignored
*** missing separator. Stop.
or
Is a directory. Stop.
Eliminate any whitespaces at the end of the PORTNAME line in
Makefile.global. Extraneous tabs or spaces will confuse the make
templates.
2.14) I have changed a source file, but a recompile does not see the
change?
The Makefiles do not have the proper dependencies. You have to
do a 'make clean' and then another 'make'.
----------------------------------------------------------------------
Section 3: Postgres95 Features
----------------------------------------------------------------------
3.1) How do I specify a KEY or other constraints on a column?
Column constraints are not supported in postgres95.
As a consequence, the system does not check for duplicates.
3.2) Does Postgres95 support nested subqueries?
Subqueries are not implemented, but they can be simulated using sql
functions.
3.3) How do I define a unique indices?
Postgres95 does not support unique indices. Defining an index does
not preclude insertion of duplicate index key values.
3.4) I've having a lot of problems with using rules.
Currently, the rule system in postgres95 is mostly broken. It
works enough to support the view mechanism, but that's about it. Use
postgres95 rules at your own peril.
3.5) I can't seem to write into the middle of large objects reliably.
The Inversion large object system in postgres95 is also
mostly broken. It works well enough for storing large wads
of data and reading them back out, but the implementation has
some underlying problems. Use postgres95 large objects at
your own peril.
3.6) Does postgres95 have a graphical user interface? A report
generator? A embedded query language interface?
No. No. No. Not in the official distribution at least. Some
users have reported some success at using 'pgbrowse' and 'onyx' as
frontends to postgres95. Several contributions are working on
tk based frontend tools. Ask on the mailing list.
3.7) How can I write client applications to Postgres95?
Postgres95 supports a C-callable library interface called libpq
as well as a Tcl-based library interface called libtcl.
Others have contributed a perl interface and a WWW gateway
to postgres95. See the postgres95 home pages for more details.
3.8) How do I prevent other hosts from accessing my Postgres95
backend?
Use host-based authentication by modifying the file
$PGDATA/pg_hba accordingly.
3.9) How do I set up a pg_group?
Currently, there is no easy interface to set up user groups.
You have to explicitly insert/update the pg_group table. For example:
jolly=> insert into pg_group (groname, grosysid, grolist)
jolly=> values ('posthackers', '1234', '{5443, 8261}');
INSERT 548224
jolly=> grant insert on foo to group posthackers;
CHANGE
jolly=>
The fields in pg_group are:
groname: the group name. This a char16 and should
be purely alphanumeric. Do not include underscores
or other punctuation.
grosysid: the group id. This is an int4.
This should be unique for each group.
grolist: the list of pg_user id's that belong in the group.
This is an int4[].
3.10) What is the exact difference between binary cursors and normal cursors?
Normal cursors return data back in ASCII format. Since data is stored
natively in binary format, the system must do a conversion to produce
the ASCII format. In addition, ASCII formats are often large in size
than binary format. Once the attributes come back in ASCII, often the
client application then has to convert it to a binary format to
manipulate it anyway.
Binary cursors give you back the data in the native binary
representation. Thus, binary cursors will tend to be a little faster
since there's less overhead of conversion.
However, ASCII is architectural neutral whereas binary representation
can differ between different machine architecture. Thus, if your client
machine uses a different representation than you server machine, getting
back attributes in binary format is probably not what you want. Also,
if your main purpose is displaying the data in ASCII, then getting it
back in ASCII will save you some effort on the client side.
3.11) Why doesn't the != operator work?
SQL specifies <> as the inequality operator, and that is what
we have defined for the built-in types. You are free, however, to
extend postgres95 to include the != operator if you like.
3.12) What is a R-tree index and what is it used for?
An r-tree index is used for indexing spatial data. A hash index can't
handle range searches. A B-tree index only handles range searches in a
single dimension. R-tree's can handle multi-dimensional data. For
example, if a R-tree index can be built on an attribute of type
'point', the system can more efficient answer queries like select all
points within a bounding rectangle.
The canonical paper that describes the original R-Tree design is:
Guttman, A. "R-Trees: A Dynamic Index Structure for Spatial Searching."
Proc of the 1984 ACM SIGMOD Int'l Conf on Mgmt of Data, 45-57.
You can also find this paper in Stonebraker's "Readings in Database
Systems"
3.13) What is the maximum size for a tuple?
Tuples are limited to 8K bytes. Taking into account system attributes
and other overhead, one should stay well shy of 8,000 bytes to be on
the safe side. To use attributes larger than 8K, try using the large
objects interface.
Tuples do not cross 8k boundaries so a 5k tuple will require 8k
of storage.
3.14) I defined indices but my queries don't seem to make use of them. Why?
Postgres95 does not automatically maintain statistics. One has to
make an explicit 'vacuum' call to update the statistics. After
statistics are updated, the optimizer has a better shot at using
indices. Note that the optimizer is limited and does not use indices
in some circumstances (such as OR clauses).
If the system still does not see the index, it is probably because you
have created an index on a field with the improper *_ops type. For
example, you have created a CHAR(4) field, but have specified a
char_ops index type_class.
See the create_index manual page for information on what type classes
are available. It must match the field type.
Postgres does not warn the user when the improper index is created.
Indexes not used for ORDER BY operations.
3.15) Are there ODBC drivers for Postgres95?
PostODBC is available as an ODBC driver for Postgres95.
For all people being interested in PostODBC, a freely available ODBC
driver for Postgres95, there are now two mailing lists devoted to the
discussion of PostODBC. The mailing lists are:
postodbc-users@listserv.direct.net
and
postodbc-developers@listserv.direct.net
these lists are ordinary majordomo mailing lists. You can subscribe
by sending a mail to
majordomo@listserv.direct.net
3.16) How do I use postgres for multi-dimensional indexing (> 2 dimensions)?
Builtin R-Trees can handle polygons and boxes. In theory, R-trees can
be extended to handle higher number of dimensions. In practice,
extending R-trees require a bit of work and we don't currently have
any documentation on how to do it.
3.17) How do I do regular expression searches? case-insensitive
regexp searching?
Postgres95 supports the SQL LIKE syntax as well as more general
regular expression searching with the ~ operator. The !~ is the
negated regexp operator. ~* and !~* are the case-insensitive regular
expression operators.
3.18) I can't access the database as the 'root' user.
You should not create database users with user id 0(root). They will
be unable to access the database. This is a security precaution
because of the ability of any user to dynamically link object modules
into the database engine.
3.19) I experienced a server crash during a vacuum. How do I remove the
lock file?
If the server crashes during a vacuum command, chances are it will
leave a lock file hanging around. Attempts to re-run the vacuum
command result in
WARN:can't create lock file -- another vacuum cleaner running?
If you are sure that no vacuum is actually running, you can remove the
file called "pg_vlock" in your database directory (which is
$PGDATA/base/<dbName>)
3.20) What is the difference between the various character types?
Type Internal Name Notes
--------------------------------------------------
CHAR char 1 character }
CHAR2 char2 2 characters }
CHAR4 char4 4 characters } optimized for a fixed length
CHAR8 char8 8 characters }
CHAR16 char16 16 characters }
CHAR(#) bpchar blank padded to the specified fixed length
VARCHAR(#) varchar size specifies maximum length, no padding
TEXT text length limited only by maximum tuple length
BYTEA bytea variable-length array of bytes
Remember, you need to use the internal name when creating indexes
on these fields or when doing other internal operations.
The last four types above are "varlena" types (i.e. the first
four bytes is the length, followed by the data). CHAR(#) and
VARCHAR(#) allocate the maximum number of bytes no matter how
much data is stored in the field. TEXT and BYTEA are the only
character types that have variable length on the disk.
3.21) In a query, how do I detect if a field is NULL?
Postgres95 has two builtin keywords, "isnull" and "notnull" (note no
spaces). For example:
select * from tbl where field isnull
will return rows from tbl where the field is null valued.
3.22) How do I see how the query optimizer is evaluating my query?
Place the word 'EXPLAIN' at the beginning of the query, for example:
EXPLAIN SELECT * FROM table1 WHERE age = 23;
3.23) How do I create a serial field?
There is no way to create a serial or unique field in Postgres95. You
can use each row's oid field as a unique value. However, if you need
to dump and reload the database, you will be assigned new oid's.
There is no way to restore the original oids.
One valid way of doing this is to create a function:
create table my_oids (f1 int4);
insert into my_oids values (1);
create function new_oid () returns int4 as
'update my_oids set f1 = f1 + 1; select f1 from my_oids; '
language 'sql';
then:
create table my_stuff (my_key int4, value text);
insert into my_stuff values (new_oid(), 'hello');
However, keep in mind there is a race condition here where one
server could do the update, then another one do an update, and
they both could select the same new id. This statement should
be performed within a transaction.
3.24) How do I create a multi-column index?
You can not directly create a multi-column index using create index.
You need to define a function which acts on the multiple columns, then
use create index with that function.
3.25) What are the temp_XXX files in my database directory?
They are temp_ files generated by the query executor. For example,
if a sort needs to be done to satisfy an ORDER BY, some temp files are
generated as a result of the sort.
If you have no transactions or sorts running at the time, it is safe to
delete the temp_ files.
3.26) Why are my table files not getting any smaller after a delete?
If you run vacuum, unused rows will be marked for reuse, but the file
blocks are not released. We could move the unused rows to the end of
the file and use ftruncate() to decrease the file size, but no one has
implemented this yet.
3.27) Why can't I connect to my database from another machine?
The default configuration allows only connections from tcp/ip host
localhost. You need to add a host entry to the file
postgres95/data/pg_hba.
3.28) I get the error 'default index class unsupported' when creating an
index. How do I do it?
You probably used:
create index idx1 on person using btree (name);
Postgres95 indexes are extensible, and therefore you must specify a
class_type when creating an index. Read the manual page for create
index (called create_index).
3.29) Why does creating an index crash the backend server?
You have probably defined an incorrect *_ops type class for the field
you are indexing.
3.30) How do I specify a decimal constant as a float8, or a string as a text?
Use the :: operator. It is needed only when the default promotion
rules fail. i.e.:
insert into tab1 values (4.23::float8, '2343'::text)
3.31) How do I find out what indexes or operations are defined in the
database?
Run the file postgres95/src/tutorial/syscat.source. It illustrates
many of the 'select's needed to get information out of the database
system tables.
3.32) My database is corrupt. I can't do anything. What should I do?
The 1.02 release has a README file and utility that describes a
possible cause of the problem and a workaround. See the file
postgres95/contrib/zap_ltv/README for more information. Also
please contact the README author to help generate a complete
fix for this bug.
This bug may be fixed in 1.02.
3.33) Createdb, destroydb, createuser,destroyuser don't run. Why?
Release 1.02 does not have this problem.
The 1.01 release of postgres95 uses a variable called PAGER to
filter the output of SELECT statements. Unfortunately, this
PAGER is used even when the standard output is not a terminal.
Upgrade to 1.02, due out August 1996, or undefine your PAGER
variable. There is also a patch located in the July archives of
the mailing list that fixes this problem on 1.01.
3.34) Why does 'createuser' return 'unexpected last match in input()'?
You have compile postgres with flex version 2.5.3. There is bug
in this version of flex. Use flex version 2.5.2 instead. There
is a doc/README.flex file which will properly patch the flex 2.5.3
source code.
3.35) All my servers crash under concurrent table access. Why?
This problem can be caused by a kernel that is not configured to
support semaphores.
3.36) What tools are available for hooking postgres to Web pages?
For web integration, PHP/FI is an excellent interface. The URL for
that is http://www.vex.net/php/
PHP is great for simple stuff, but for more complex stuff, some
still use the perl interface and CGI.pm.
An example of using WWW with C to talk to Postgres is can be
tried at:
http://www.ki.net/~mlc
3.37) What is the time-warp feature and how does it relate to vacuum?
Postgres95 handles data changes differently than most database
systems. When a row is changed in a table, the original row
is marked with the time it was changed, and a new row is created
with the current data. By default, only current rows are used
in a table. If you specify a date/time after the table name in
a FROM clause, you can access the data that was current at that
time, i.e.
SELECT *
FROM employees ['July 24, 1996 09:00:00']
displays employee rows in the table at the specified time.
You can specify intervals like [date,date], [date,], [,date],
or [,]. This last option accesses all rows that ever existed.
INSERTed rows get a timestamp too, so rows that were not in
the table at the desired time will not appear.
Vacuum removes rows that are no longer current. This time-warp
feature is used by the engine for rollback and crash recovery.
3.38) How do I tune the database engine for better performace?
There are two things that can be done. You can use Openlink's
option to disable fsync() by starting the postmaster with a
'-o -F' option. This will prevent fsync()'s from flushing to
disk after every transaction.
You can also use the postmaster -B option to increase the number
of shared memory buffers shared among the backend processes. If
you make this parameter too high, the process will not start or
crash unexpectedly. Each buffer is 8K and the defualt is 64
buffers.
----------------------------------------------------------------------
Section 4: Extending Postgres95
----------------------------------------------------------------------
4.1) I wrote a user-defined function and when I run it in psql, it
dumps core.
The problem could be a number of things. Try testing your
user-defined function in a stand alone test program first.
Also, make sure you are not sending elog NOTICES when the front-end
is expecting data, such as during a type_in() or type_out()
functions
4.2) I get messages of the type
NOTICE:PortalHeapMemoryFree: 0x402251d0 not in alloc set!
You are pfree'ing something that was not palloc'ed. When writing
user-defined functions, do not include the file
"libpq-fe.h". Doing so will cause your palloc to be a malloc
instead of a free. Then, when the backend pfrees the storage,
you get the notice message.
4.3) I've written some nifty new types and functions for Postgres95.
Please share them with other postgres95 users. Send your
extensions to mailing list, and they will eventually end up in
the contrib/ subdirectory.
4.4) How do I write a C function to return a tuple?
This requires extreme wizardry, so extreme that the authors
have not ever tried it, though in principle it can be done.
The short answer is ... you can't. This capability is
forthcoming in the future.
----------------------------------------------------------------------
Section 5: Bugs
----------------------------------------------------------------------
5.1) How do I find out about bug fixes?
The directory ftp.ki.net:/pub/postgres95 contains patches for
the latest release.
5.2) How do I make a bug report?
First, check to see that your bug is not one that has already
been fixed (question 5.1). Then, fill out the "bug-template"
file and send it to:
pg95-dev@ki.net
This is the address of the developers mailing list.
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