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Frequently Asked Questions (FAQ) for PostgreSQL <HEAD>
<TITLE>PostgreSQL FAQ</title>
Last updated: Tue May 13 23:15:59 EDT 1997 </HEAD>
Version: 6.1 <BODY BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#FF0000" VLINK="#A00000" ALINK="#0000FF">
<H1>
Current maintainer: Bruce Momjian (maillist@candle.pha.pa.us) Frequently Asked Questions (FAQ) for PostgreSQL
</H1>
The most recent version of this document can be viewed at the <P>
postgreSQL Web site, http://postgreSQL.org. Last updated: Wed Jun 11 10:44:40 EDT 1997
<BR>
Linux-specific questions are answered in Version: 6.1
http://postgreSQL.org/docs/FAQ-Linux.phtml. <P>
Current maintainer: Bruce Momjian (<a
Irix-specific questions are answered in href="mailto:maillist@candle.pha.pa.us">maillist@candle.pha.pa.us</a>)<BR>
http://postgreSQL.org/docs/FAQ-Irix.phtml. <P>
The most recent version of this document can be viewed at
Changes in this version (* = modified, + = new): the postgreSQL Web site, <a
* 3.42) What is Genetic Query Optimization? href="http://postgreSQL.org">http://postgreSQL.org</a>.
* 3.43) I am running Solaris and my dates display wrong. Why? <P>
Linux-specific questions are answered in
_________________________________________________________________ <a href="http://postgreSQL.org/docs/FAQ-Linux.phtml">http://postgreSQL.org/docs/FAQ-Linux.phtml</a>.
<P>
Questions answered: Irix-specific questions are answered in
<a href="http://postgreSQL.org/docs/FAQ-Irix.phtml">http://postgreSQL.org/docs/FAQ-Irix.phtml</a>.
1) General questions <P>
Changes in this version (* = modified, + = new):
1.1) What is PostgreSQL? <UL>
1.2) What does PostgreSQL run on? <LI>3.42) What is Genetic Query Optimization?<BR>
1.3) Where can I get PostgreSQL? <LI>3.43) I am running Solaris and my dates display wrong. Why?<BR>
1.4) What's the copyright on PostgreSQL? </UL>
1.5) Support for PostgreSQL <HR>
1.6) Latest release of PostgreSQL <P>
1.7) Is there a commercial version of PostgreSQL? <H2>Questions answered:</H2>
1.9) What version of SQL does PostgreSQL use? <H3> 1) General questions</H3>
1.10) Does PostgreSQL work with databases from earlier versions of <a href="#1.1">1.1</a>) What is PostgreSQL?<BR>
postgres? <a href="#1.2">1.2</a>) What does PostgreSQL run on?<BR>
1.11) How many people use PostgreSQL? <a href="#1.3">1.3</a>) Where can I get PostgreSQL?<BR>
<a href="#1.4">1.4</a>) What's the copyright on PostgreSQL?<BR>
2) Installation questions <a href="#1.5">1.5</a>) Support for PostgreSQL<BR>
<a href="#1.6">1.6</a>) Latest release of PostgreSQL<BR>
2.1) initdb doesn't run <a href="#1.7">1.7</a>) Is there a commercial version of PostgreSQL?<BR>
2.2) when I start up the postmaster, I get "FindBackend: could not <a href="#1.9">1.9</a>) What version of SQL does PostgreSQL use?<BR>
find a backend to execute..." "postmaster: could not find backend to <a href="#1.10">1.10</a>) Does PostgreSQL work with databases from
execute..." earlier versions of postgres?<BR>
2.3) The system seems to be confused about commas, decimal points, and <a href="#1.11">1.11</a>) How many people use PostgreSQL?<BR>
date formats. <H3> 2) Installation questions</H3>
2.4) How do I install PostgreSQL somewhere other than <a href="#2.1">2.1</a>) initdb doesn't run<BR>
/usr/local/pgsql? <a href="#2.2">2.2</a>) when I start up the postmaster, I get
2.5) When I run postmaster, I get a Bad System Call core dumped "FindBackend: could not find a backend to execute..."
message. "postmaster: could not find backend to execute..."<BR>
2.6) I get the error message "obj/fmgr.h: No such file or directory" <a href="#2.3">2.3</a>) The system seems to be confused about commas,
2.7) When I try to start the postmaster, I get IpcMemoryCreate errors. decimal points, and date formats.<BR>
2.8) I have changed a source file, but a recompile does not see the <a href="#2.4">2.4</a>) How do I install PostgreSQL somewhere other than
change? /usr/local/pgsql?<BR>
<a href="#2.5">2.5</a>) When I run postmaster, I get a Bad System Call
3) Operational questions core dumped message.<BR>
<a href="#2.6">2.6</a>) When I try to start the postmaster, I get
3.1) How do I specify a KEY or other constraints on a column? IpcMemoryCreate errors.<BR>
3.2) Does PostgreSQL support nested subqueries? <a href="#2.7">2.7</a>) I have changed a source file, but a
3.3) How do I define a unique indices? recompile does not see the change?<BR>
3.4) I've having a lot of problems using rules. <H3> 3) Operational questions</H3>
3.5) I can't seem to write into the middle of large objects reliably. <a href="#3.1">3.1</a>) How do I specify a KEY or other constraints on a
3.6) Does PostgreSQL have a graphical user interface? A report column?<BR>
generator? A embedded query language interface? <a href="#3.2">3.2</a>) Does PostgreSQL support nested subqueries?<BR>
3.7) How can I write client applications to PostgreSQL? <a href="#3.3">3.3</a>) How do I define a unique indices?<BR>
3.8) How do I prevent other hosts from accessing my PostgreSQL <a href="#3.4">3.4</a>) I've having a lot of problems using rules.<BR>
3.9) How do I set up a pg_group? <a href="#3.5">3.5</a>) I can't seem to write into the middle of large
3.10) What is the exact difference between binary cursors and normal objects reliably.<BR>
cursors? <a href="#3.6">3.6</a>) Does PostgreSQL have a graphical user interface?
3.11) Why doesn't the != operator work? A report generator? A embedded query language interface?<BR>
3.12) What is a R-tree index and what is it used for? <a href="#3.7">3.7</a>) How can I write client applications to
3.13) What is the maximum size for a tuple? PostgreSQL?<BR>
3.14) I defined indices but my queries don't seem to make use of them. <a href="#3.8">3.8</a>) How do I prevent other hosts from accessing my
Why? PostgreSQL<BR>
3.15) Are there ODBC drivers for PostgreSQL? <a href="#3.9">3.9</a>) How do I set up a pg_group?<BR>
3.16) How do I use postgres for multi-dimensional indexing (> 2 <a href="#3.10">3.10</a>) What is the exact difference between
dimensions)? binary cursors and normal cursors?<BR>
3.17) How do I do regular expression searches? case-insensitive regexp <a href="#3.11">3.11</a>) Why doesn't the != operator work?<BR>
searching? <a href="#3.12">3.12</a>) What is a R-tree index and what is it
3.18) I can't access the database as the 'root' user. used for?<BR>
3.19) I experienced a server crash during a vacuum. How do I remove <a href="#3.13">3.13</a>) What is the maximum size for a
the lock file? tuple?<BR>
3.20) What is the difference between the various character types? <a href="#3.14">3.14</a>) I defined indices but my queries don't
3.21) In a query, how do I detect if a field is NULL? seem to make use of them. Why?<BR>
3.22) How do I see how the query optimizer is evaluating my query? <a href="#3.15">3.15</a>) Are there ODBC drivers for
3.23) How do I create a serial field? PostgreSQL?<BR>
3.24) How do I create a multi-column index? <a href="#3.16">3.16</a>) How do I use postgres for
3.25) What are the temp_XXX files in my database directory? multi-dimensional indexing (&gt; 2 dimensions)?<BR>
3.26) Why are my table files not getting any smaller after a delete? <a href="#3.17">3.17</a>) How do I do regular expression searches?
3.27) Why can't I connect to my database from another machine? case-insensitive regexp searching?<BR>
3.28) I get the error 'default index class unsupported' when creating <a href="#3.18">3.18</a>) I can't access the database as the
an index. How do I do it? 'root' user.<BR>
3.29) Why does creating an index crash the backend server? <a href="#3.19">3.19</a>) I experienced a server crash during a
3.30) How do I specify a decimal constant as a float8, or a string as vacuum. How do I remove the lock file?<BR>
a text? Why am I getting poor precision? <a href="#3.20">3.20</a>) What is the difference between the
3.31) How do I find out what indexes or operations are defined in the various character types?<BR>
database? <a href="#3.21">3.21</a>) In a query, how do I detect if a field
3.32) My database is corrupt. I can't do anything. What should I do? is NULL?<BR>
3.33) Createdb, destroydb, createuser, destroyuser don't run. Why? <a href="#3.22">3.22</a>) How do I see how the query optimizer is
3.34) Why do statements require an extra character at the end? Why evaluating my query?<BR>
does 'createuser' return 'unexpected last match in input()'? Why does <a href="#3.23">3.23</a>) How do I create a serial field?<BR>
pg_dump fail? <a href="#3.24">3.24</a>) How do I create a multi-column
3.35) All my servers crash under concurrent table access. Why? index?<BR>
3.36) What tools are available for hooking postgres to Web pages? <a href="#3.25">3.25</a>) What are the temp_XXX files in my
3.37) What is the time-warp feature and how does it relate to vacuum? database directory?<BR>
3.38) How do I tune the database engine for better performance? <a href="#3.26">3.26</a>) Why are my table files not getting any
3.39) What debugging features are available in PostgreSQL? smaller after a delete?<BR>
3.40) What is an oid? What is a tid? <a href="#3.27">3.27</a>) Why can't I connect to my database from
3.41) What is the meaning of some of the terms used in Postgres? another machine?<BR>
3.42) What is Genetic Query Optimization? <a href="#3.28">3.28</a>) I get the error 'default index class
3.42) I am running Solaris and my dates display wrong. Why? unsupported' when creating an index. How do I do it?<BR>
<a href="#3.29">3.29</a>) Why does creating an index crash the
4) Questions about extending PostgreSQL backend server?<BR>
<a href="#3.30">3.30</a>) How do I find out what indexes or
4.1) I wrote a user-defined function and when I run it in psql, it operations are defined in the database?<BR>
dumps core. <a href="#3.31">3.31</a>) Why do statements require an extra character at
4.2) I get messages of the type NOTICE:PortalHeapMemoryFree: the end? Why does 'createuser' return 'unexpected last match in
0x402251d0 input()'? Why does pg_dump fail?<BR>
4.3) I've written some nifty new types and functions for PostgreSQL. <a href="#3.32">3.32</a>) All my servers crash under concurrent
4.4) How do I write a C function to return a tuple? table access. Why?<BR>
<a href="#3.33">3.33</a>) What tools are available for hooking
5) Bugs postgres to Web pages?<BR>
<a href="#3.34">3.34</a>) What is the time-warp feature and how
5.1) How do I make a bug report? does it relate to vacuum?<BR>
_________________________________________________________________ <a href="#3.35">3.35</a>) How do I tune the database engine for
better performance?<BR>
Section 1: General Questions <a href="#3.36">3.36</a>) What debugging features are available in
PostgreSQL?<BR>
1.1) What is PostgreSQL? <a href="#3.37">3.37</a>) What is an oid? What is a tid?<BR>
<a href="#3.38">3.38</a>) What is the meaning of some of the terms
PostgreSQL is an enhancement of the POSTGRES database management used in Postgres?<BR>
system, a next-generation DBMS research prototype. While PostgreSQL <a href="#3.39">3.39</a>) What is Genetic Query Optimization?<BR>
retains the powerful data model and rich data types of POSTGRES, it <a href="#3.40">3.40</a>) I am running Solaris and my dates
replaces the PostQuel query language with an extended subset of SQL. display wrong. Why?
PostgreSQL is free and the complete source is available. <a href="#3.41">3.41</a>) How do I enable more than 32 concurrent
backends?
PostgreSQL development is being performed by a team of Internet <H3> 4) Questions about extending PostgreSQL</H3>
developers who all subscribe to the PostgreSQL development mailing <a href="#4.1">4.1</a>) I wrote a user-defined function and when I run
list. The current coordinator is Marc G. Fournier it in psql, it dumps core.<BR>
(scrappy@postgreSQL.org). (See below on how to join). This team is now <a href="#4.2">4.2</a>) I get messages of the type
responsible for all current and future development of PostgreSQL. NOTICE:PortalHeapMemoryFree: 0x402251d0<BR>
<a href="#4.3">4.3</a>) I've written some nifty new types and functions
The authors of PostgreSQL 1.01 were Andrew Yu and Jolly Chen. Many for PostgreSQL.<BR>
others have contributed to the porting, testing, debugging and <a href="#4.4">4.4</a>) How do I write a C function to return a
enhancement of the code. The original Postgres code, from which tuple?<BR>
PostgreSQL is derived, was the effort of many graduate students, <H3> 5) Bugs</H3>
undergraduate students, and staff programmers working under the <a href="#5.1">5.1</a>) How do I make a bug report?
direction of Professor Michael Stonebraker at the University of
California, Berkeley. <HR> <H2> Section 1: General Questions</H2> <H3><a
name="1.1">1.1</a>) What is PostgreSQL?</H3>
The original name of the software at Berkeley was Postgres. When SQL
functionality was added in 1995, its name was changed to Postgres95. <P>
The name was changed at the end of 1996 to PostgreSQL. PostgreSQL is an enhancement of the POSTGRES database management system,
a next-generation DBMS research prototype. While PostgreSQL retains the
1.2) What does PostgreSQL run on? powerful data model and rich data types of POSTGRES, it replaces the
PostQuel query language with an extended subset of SQL. PostgreSQL is
The authors have compiled and tested PostgreSQL on the following free and the complete source is available.
platforms(some of these compiles require gcc 2.7.0): <P>
* aix - IBM on AIX 3.2.5 PostgreSQL development is being performed by a team of Internet
* alpha - DEC Alpha AXP on OSF/1 2.0 developers who all subscribe to the PostgreSQL development mailing list.
* BSD44_derived - OSs derived from 4.4-lite BSD (NetBSD, FreeBSD) The current coordinator is Marc G. Fournier (<a
* bsdi - BSD/OS 2.0, 2.01, 2.1, 3.0 href="mailto:scrappy@postgreSQL.org">scrappy@postgreSQL.org</a>). (See
* dgux - DG/UX 5.4R3.10 below on how to join). This team is now responsible for all current and
* hpux - HP PA-RISC on HP-UX 9.0 future development of PostgreSQL.
* i386_solaris - i386 Solaris <P>
* irix5 - SGI MIPS on IRIX 5.3 The authors of PostgreSQL 1.01 were Andrew Yu and Jolly Chen. Many
* linux - Intel x86 on Linux 1.2 and Linux ELF (For non-ELF Linux, others have contributed to the porting, testing, debugging and
see LINUX_ELF below). enhancement of the code. The original Postgres code, from which
* sparc_solaris - SUN SPARC on Solaris 2.4 PostgreSQL is derived, was the effort of many graduate students,
* sunos4 - SUN SPARC on SunOS 4.1.3 undergraduate students, and staff programmers working under the
* svr4 - Intel x86 on Intel SVR4 direction of Professor Michael Stonebraker at the University of
* ultrix4 - DEC MIPS on Ultrix 4.4 California, Berkeley.
<P>
The following platforms have known problems/bugs: The original name of the software at Berkeley was Postgres. When SQL
* nextstep - Motorola MC68K or Intel x86 on NeXTSTEP 3.2 functionality was added in 1995, its name was changed to Postgres95. The
name was changed at the end of 1996 to PostgreSQL.
1.3) Where can I get PostgreSQL? <P>
<H3><a name="1.2">1.2</a>) What does PostgreSQL run
The primary anonymous ftp site for PostgreSQL is: on?</H3>
* ftp://ftp.postgreSQL.org/pub <P>
The authors have compiled and tested PostgreSQL on the following
A mirror site exists at: platforms(some of these compiles require gcc 2.7.0):
* ftp://postgres95.vnet.net/pub/postgres95 <UL>
* ftp://ftp.luga.or.at/pub/postgres95 <LI> aix - IBM on AIX 3.2.5
* ftp://cal011111.student.utwente.nl/pub/postgres95 <LI> alpha - DEC Alpha AXP on OSF/1 2.0
* ftp://ftp.uni-trier.de/pub/database/rdbms/postgres/postgres95 <LI> BSD44_derived - OSs derived from 4.4-lite BSD (NetBSD, FreeBSD)
* ftp://rocker.sch.bme.hu <LI> bsdi - BSD/OS 2.0, 2.01, 2.1, 3.0
<LI> dgux - DG/UX 5.4R3.10
1.4) What's the copyright on PostgreSQL? <LI> hpux - HP PA-RISC on HP-UX 9.0
<LI> i386_solaris - i386 Solaris
PostgreSQL is subject to the following COPYRIGHT. <LI> irix5 - SGI MIPS on IRIX 5.3
<LI> linux - Intel x86 on Linux 1.2 and Linux ELF
PostgreSQL Data Base Management System (For non-ELF Linux, see LINUX_ELF below).
<LI> sparc_solaris - SUN SPARC on Solaris 2.4
Copyright (c) 1994-6 Regents of the University of California <LI> sunos4 - SUN SPARC on SunOS 4.1.3
<LI> svr4 - Intel x86 on Intel SVR4
Permission to use, copy, modify, and distribute this software and its <LI> ultrix4 - DEC MIPS on Ultrix 4.4
documentation for any purpose, without fee, and without a written </UL>
agreement is hereby granted, provided that the above copyright notice The following platforms have known problems/bugs:
and this paragraph and the following two paragraphs appear in all <UL>
copies. <LI> nextstep - Motorola MC68K or Intel x86 on NeXTSTEP 3.2
</UL>
IN NO EVENT SHALL THE UNIVERSITY OF CALIFORNIA BE LIABLE TO ANY PARTY <P>
FOR DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES, <H3><a name="1.3">1.3</a>) Where can I get PostgreSQL?</H3>
INCLUDING LOST PROFITS, ARISING OUT OF THE USE OF THIS SOFTWARE AND <P> The primary anonymous ftp site for PostgreSQL is:
ITS DOCUMENTATION, EVEN IF THE UNIVERSITY OF CALIFORNIA HAS BEEN <UL>
ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. <LI> <a
href="ftp://ftp.postgreSQL.org/pub">ftp://ftp.postgreSQL.org/pub</a>
THE UNIVERSITY OF CALIFORNIA SPECIFICALLY DISCLAIMS ANY WARRANTIES, </UL>
INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF <P> A mirror site exists at:
MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE SOFTWARE <UL>
PROVIDED HEREUNDER IS ON AN "AS IS" BASIS, AND THE UNIVERSITY OF <LI> <a
CALIFORNIA HAS NO OBLIGATIONS TO PROVIDE MAINTENANCE, SUPPORT, href="ftp://postgres95.vnet.net/pub/postgres95">ftp://postgres95.vnet.net/pub/postgres95</a>
UPDATES, ENHANCEMENTS, OR MODIFICATIONS. <LI> <a
href="ftp://ftp.luga.or.at/pub/postgres95">ftp://ftp.luga.or.at/pub/postgres95</a>
1.5) Support for PostgreSQL <LI> <a
href="ftp://cal011111.student.utwente.nl/pub/postgres95">ftp://cal011111.student.utwente.nl/pub/postgres95</a>
There is no official support for PostgreSQL from the original <LI> <a
maintainers or from University of California, Berkeley. It is href="ftp://ftp.uni-trier.de/pub/database/rdbms/postgres/postgres95">ftp://ftp.uni-trier.de/pub/database/rdbms/postgres/postgres95</a>
maintained through volunteer effort only. <LI> <a
href="ftp://rocker.sch.bme.hu">ftp://rocker.sch.bme.hu</a>
The main mailing list is: questions@postgreSQL.org. It is available </UL>
for discussion o f matters pertaining to PostgreSQL, including but not <H3><a name="1.4">1.4</a>) What's the copyright on
limited to bug reports and fixes. For info on how to subscribe, send a PostgreSQL?</H3>
mail with the lines in the body (not the subject line) <P>
PostgreSQL is subject to the following COPYRIGHT.
<P>
PostgreSQL Data Base Management System
<P>
Copyright (c) 1994-6 Regents of the University of California
<P>
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.
<P>
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.
<P>
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.
<P>
<H3><a name="1.5">1.5</a>) Support for PostgreSQL </H3>
<P>
There is no official support for PostgreSQL from the original
maintainers or from University of California, Berkeley. It is
maintained through volunteer effort only.
<P>
The main mailing list is: <a
href="mailto:questions@postgreSQL.org">questions@postgreSQL.org</a>. It
is available for discussion o f matters pertaining to PostgreSQL,
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)
<PRE>
<CODE>
subscribe subscribe
end end
</CODE>
to questions-request@postgreSQL.org. </PRE>
<P>
There is also a digest list available. To subscribe to this list, send to <a
email to: questions-digest-request@postgreSQL.org with a BODY of: href="mailto:questions-request@postgreSQL.org">questions-request@postgreSQL.org</a>.
<P>
There is also a digest list available. To subscribe to this list, send
email to:
<a
href="mailto:questions-digest-request@postgreSQL.org">
questions-digest-request@postgreSQL.org</a> with a BODY of:
<PRE>
<KBD>
subscribe subscribe
end end
</KBD>
Digests are sent out to members of this list whenever the main list </PRE>
has received around 30k of messages. Digests are sent out to members of this list whenever the main list has
received around 30k of messages.
There is a bugs mailing list available. To subscribe to this list, <P>
send email to bugs-request@postgreSQL.org with a BODY of: There is a bugs mailing list available. To subscribe to this
list, send email to <a
There is also a developers discussion mailing list available. To href="mailto:bugs-request@postgreSQL.org">bugs-request@postgreSQL.org</a>
subscribe to this list, send email to hackers-request@postgreSQL.org with a BODY of:
with a BODY of: <P>
There is also a developers discussion mailing list available. To subscribe to this
list, send email to <a
href="mailto:hackers-request@postgreSQL.org">hackers-request@postgreSQL.org</a>
with a BODY of:
<P>
<PRE>
<KBD>
subscribe subscribe
end end
</KBD>
Additional information about PostgreSQL can be found via the </PRE>
PostgreSQL WWW home page at: <P>
Additional information about PostgreSQL can be found via the PostgreSQL
http://postgreSQL.org WWW home page at:
<BLOCKQUOTE>
1.6) Latest release of PostgreSQL <a
href="http://postgreSQL.org">http://postgreSQL.org</a>
The latest release of PostgreSQL is version 6.0, which was released on </BLOCKQUOTE>
January 31, 1997. 6.1 is scheduled for release soon. For information <P>
about what is new in 6.1, see our TODO list on our WWW page. <H3><a name="1.6">1.6</a>) Latest release of PostgreSQL</H3>
<P>
We expect a 7.0 release in several months that will remove time-travel The latest release of PostgreSQL is version 6.0, which was released on
and reduce by 50% the size of on-disk system columns maintained for January 31, 1997. 6.1 is scheduled for release soon. For information
each row in a table. This release will also require a dump and about what is new in 6.1, see our TODO list on our WWW page.
restore. <P>
We expect a 7.0 release in several months that will remove time-travel
1.7) Is there a commercial version of PostgreSQL? and reduce by 50% the size of on-disk system columns maintained for each
row in a table. This release will also require a dump and restore.
Illustra Information Technology (a wholly owned subsidiary of Informix <P>
Software, Inc.) sells an object-relational DBMS called Illustra that <H3><a name="1.7">1.7</a>) Is there a commercial version of PostgreSQL?</H3>
was originally based on postgres. Illustra has cosmetic similarities <P>
to PostgreSQL but has more features, is more robust, performs better, Illustra Information Technology (a wholly owned subsidiary of Informix
and offers real documentation and support. On the flip side, it costs Software, Inc.) sells an object-relational DBMS called Illustra that was
money. For more information, contact sales@illustra.com originally based on postgres. Illustra has cosmetic similarities to
PostgreSQL but has more features, is more robust, performs better, and
1.8) What documentation is available for PostgreSQL? offers real documentation and support. On the flip side, it costs
money. For more information, contact <a
A user manual, manual pages, and some small test examples are included href="mailto:sales@illustra.com">sales@illustra.com</a>
in the distribution. The sql and built-in manual pages are <P>
particularly important. <H3><a name="1.8">1.8</a>) What documentation is available for PostgreSQL?</H3>
<P>
The www page contains pointers to an implementation guide and five A user manual, manual pages, and some small test examples are included
papers written about postgres design concepts and features. in the distribution. The sql and built-in manual pages are particularly
important.
1.9) What version of SQL does PostgreSQL use? <P>
The www page contains pointers to an implementation guide and five
PostgreSQL supports a subset of SQL-92. It has most of the important papers written about postgres design concepts and features.
constructs but lacks some of the functionality. The most visible <P>
differences are: <H3><a name="1.9">1.9</a>) What version of SQL does PostgreSQL use?</H3>
* no support for nested subqueries <P>
* no HAVING clause under a GROUP BY PostgreSQL supports a subset of SQL-92. It has most of the important
constructs but lacks some of the functionality. The most visible
On the other hand, you get to create user-defined types, functions, differences are:
inheritance etc. If you're willing to help with PostgreSQL coding, <UL>
eventually we can also add the missing features listed above. <LI> no support for nested subqueries
<LI> no HAVING clause under a GROUP BY
1.10) Does PostgreSQL work with databases from earlier versions of postgres? </UL>
<P>
PostgreSQL v1.09 is compatible with databases created with v1.01. On the other hand, you get to create user-defined types, functions,
Those upgrading from 1.0 should read the directions in the inheritance etc. If you're willing to help with PostgreSQL coding,
MIGRATION_1.0_TO_1.02 directory. eventually we can also add the missing features listed above.
<P>
Upgrading to 6.0 requires a dump and restore from previous releases. <H3><a name="1.10">1.10</a>) Does PostgreSQL work with databases from
earlier versions of postgres?</H3>
1.11) How many people use PostgreSQL? <P>
PostgreSQL v1.09 is compatible with databases created with v1.01. Those
Since we don't have any licensing or registration scheme, it's upgrading from 1.0 should read the directions in the
impossible to tell. We do know hundreds copies of PostgreSQL v1.* have MIGRATION_1.0_TO_1.02 directory.
been downloaded, and that there many hundreds of subscribers to the <P>
mailing lists. Upgrading to 6.0 requires a dump and restore from previous releases.
<P>
_________________________________________________________________ Upgrading to 6.1 requires a dump and restore from previous releases.
<P>
Section 2: Installation Questions Those ugrading from versions earlier than 1.09 must upgrade to 1.09
first without a dump/reload, then dump the data from 1.09, and then load
2.1) initdb doesn't run it into 6.0 or 6.1.
<P>
* check to see that you have the proper paths set <H3><a name="1.11">1.11</a>) How many people use PostgreSQL?</H3>
* check that the 'postgres' user owns all the right files <P>
* ensure that there are files in $PGDATA/files, and that they are Since we don't have any licensing or registration scheme, it's
non-empty. If they aren't, then "gmake install" failed for some impossible to tell. We do know hundreds copies of PostgreSQL v1.* have
reason been downloaded, and that there many hundreds of subscribers to the
mailing lists.
2.2) when I start up the postmaster, I get "FindBackend: could not find a <P>
backend to execute..." "postmaster: could not find backend to execute..." <HR>
<H2> Section 2: Installation Questions
You probably do not have the right path set up. The 'postgres' </H2>
executable needs to be in your path. <P>
<H3><a name="2.1">2.1</a>) initdb doesn't run</H3>
2.3) The system seems to be confused about commas, decimal points, and date <P>
formats. <UL>
<LI> check to see that you have the proper paths set
Check your locale configuration. PostgreSQL uses the locale settings <LI> check that the 'postgres' user owns all the right files
of the user that ran the postmaster process. Set those accordingly for <LI> ensure that there are files in $PGDATA/files, and that they
your operating environment. are non-empty. If they aren't, then "gmake install" failed for
some reason
2.4) How do I install PostgreSQL somewhere other than /usr/local/pgsql? </UL>
<P>
You need to edit Makefile.global and change POSTGRESDIR accordingly, <H3><a name="2.2">2.2</a>) when I start up the postmaster, I get
or create a Makefile.custom and define POSTGRESDIR there. "FindBackend: could not find a backend to execute..."
"postmaster: could not find backend to execute..."</H3>
2.5) When I run postmaster, I get a Bad System Call core dumped message. <P>
You probably do not have the right path set up. The 'postgres'
It could be a variety of problems, but first check to see that you executable needs to be in your path.
have system V extensions installed on your kernel. PostgreSQL requires <P>
kernel support for shared memory. <H3><a name="2.3">2.3</a>) The system seems to be confused about commas,
decimal points, and date formats.</H3>
2.6) I get the error message "obj/fmgr.h: No such file or directory" <P>
Check your locale configuration. PostgreSQL uses the locale settings of
This indicates that you did not generate the file fmgr.h properly. the user that ran the postmaster process. Set those accordingly for
Something failed in the running of the your operating environment.
src/backend/utils/Gen_fmgrtab.sh script. Check to see the paths used <P>
in that script is appropriate to your system. <H3><a name="2.4">2.4</a>) How do I install PostgreSQL somewhere other than
/usr/local/pgsql?</H3>
2.7) When I try to start the postmaster, I get IpcMemoryCreate errors. <P>
You need to edit Makefile.global and change POSTGRESDIR accordingly, or
You either do not have shared memory configured properly in kernel or create a Makefile.custom and define POSTGRESDIR there.
you need to enlarge the shared memory available in the kernel. The <P>
exact amount you need depends on your architecture and how many <H3><a name="2.5">2.5</a>) When I run postmaster, I get a Bad System
buffers you configure postmaster to run with. For most systems, with Call core dumped message.</H3>
default buffer sizes, you need a minimum of ~760K. <P>
It could be a variety of problems, but first check to see that you have
2.8) I have changed a source file, but a recompile does not see the change? system V extensions installed on your kernel. PostgreSQL requires kernel
support for shared memory.
The Makefiles do not have the proper dependencies for include files. <P>
You have to do a 'make clean' and then another 'make'. <H3><a name="2.6">2.6</a>) When I try to start the postmaster, I get
IpcMemoryCreate errors.</H3>
_________________________________________________________________ <P>
You either do not have shared memory configured properly in kernel or
Section 3: PostgreSQL Features you need to enlarge the shared memory available in the kernel. The
exact amount you need depends on your architecture and how many buffers
3.1) How do I specify a KEY or other constraints on a column? you configure postmaster to run with. For most systems, with default
buffer sizes, you need a minimum of ~760K.
Column constraints are not supported in PostgreSQL. As a consequence, <P>
the system does not check for duplicates. <H3><a name="2.7">2.7</a>) I have changed a source file, but a
recompile does not see the change?</H3>
Under 6.0, create a unique index on the column. Attempts to create <P>
duplicate of that column will report an error. The Makefiles do not have the proper dependencies for include files. You
have to do a 'make clean' and then another 'make'.
3.2) Does PostgreSQL support nested subqueries? <P>
<HR>
Subqueries are not implemented, but they can be simulated using sql <H2> Section 3: PostgreSQL Features
functions. </H2>
3.3) How do I define a unique indices? <P>
<H3><a name="3.1">3.1</a>) How do I specify a KEY or other constraints on a
PostgreSQL 6.0 supports unique indices. column?</H3>
<P>
3.4) I've having a lot of problems using rules. Column constraints are not supported in PostgreSQL. As a consequence,
the system does not check for duplicates.
Currently, the rule system in PostgreSQL is mostly broken. It works <P>
enough to support the view mechanism, but that's about it. Use Under 6.0, create a unique index on the column. Attempts to create
PostgreSQL rules at your own peril. duplicate of that column will report an error.
<P>
3.5) I can't seem to write into the middle of large objects reliably. <H3><a name="3.2">3.2</a>) Does PostgreSQL support nested subqueries?</H3>
<P>
The Inversion large object system in PostgreSQL is also mostly broken. Subqueries are not implemented, but they can be simulated using sql
It works well enough for storing large wads of data and reading them functions.
back out, but the implementation has some underlying problems. Use <P>
PostgreSQL large objects at your own peril. <H3><a name="3.3">3.3</a>) How do I define a unique indices?</H3>
<P>
3.6) Does PostgreSQL have a graphical user interface? A report generator? A PostgreSQL 6.0 supports unique indices.
embedded query language interface? <P>
<H3><a name="3.4">3.4</a>) I've having a lot of problems using rules.</H3>
No. No. No. Not in the official distribution at least. Some users have <P>
reported some success at using 'pgbrowse' and 'onyx' as frontends to Currently, the rule system in PostgreSQL is mostly broken. It works
PostgreSQL. Several contributions are working on tk based frontend enough to support the view mechanism, but that's about it. Use
tools. Ask on the mailing list. PostgreSQL rules at your own peril.
<P>
3.7) How can I write client applications to PostgreSQL? <H3><a name="3.5">3.5</a>) I can't seem to write into the middle of large
objects reliably.</H3>
PostgreSQL supports a C-callable library interface called libpq as <P>
well as a Tcl-based library interface called libtcl. The Inversion large object system in PostgreSQL is also mostly broken.
It works well enough for storing large wads of data and reading them
Others have contributed a perl interface and a WWW gateway to back out, but the implementation has some underlying problems. Use
PostgreSQL. See the PostgreSQL home pages for more details. PostgreSQL large objects at your own peril.
<P>
3.8) How do I prevent other hosts from accessing my PostgreSQL backend? <H3><a name="3.6">3.6</a>) Does PostgreSQL have a graphical user interface?
A report generator? A embedded query language interface?</H3>
Use host-based authentication by modifying the file $PGDATA/pg_hba <P>
accordingly. No. No. No. Not in the official distribution at least. Some users have
reported some success at using 'pgbrowse' and 'onyx' as frontends to
3.9) How do I set up a pg_group? PostgreSQL. Several contributions are working on tk based frontend
tools. Ask on the mailing list.
Currently, there is no easy interface to set up user groups. You have <P>
to explicitly insert/update the pg_group table. For example: <H3><a name="3.7">3.7</a>) How can I write client applications to PostgreSQL?</H3>
<P>
PostgreSQL supports a C-callable library interface called libpq as well
jolly=> insert into pg_group (groname, grosysid, grolist) as a Tcl-based library interface called libtcl.
jolly=> values ('posthackers', '1234', '{5443, 8261}'); <P>
Others have contributed a perl interface and a WWW gateway to
PostgreSQL. See the PostgreSQL home pages for more details.
<P>
<H3><a name="3.8">3.8</a>) How do I prevent other hosts from accessing my
PostgreSQL backend?</H3>
<P>
Use host-based authentication by modifying the file $PGDATA/pg_hba
accordingly.
<P>
<H3><a name="3.9">3.9</a>) How do I set up a pg_group?</H3>
<P>
Currently, there is no easy interface to set up user groups. You have to
explicitly insert/update the pg_group table. For example:
<PRE>
<CODE>
jolly=&gt; insert into pg_group (groname, grosysid, grolist)
jolly=&gt; values ('posthackers', '1234', '{5443, 8261}');
INSERT 548224 INSERT 548224
jolly=> grant insert on foo to group posthackers; jolly=&gt; grant insert on foo to group posthackers;
CHANGE CHANGE
jolly=> jolly=&gt;
</CODE>
</PRE>
<P>
The fields in pg_group are: The fields in pg_group are:
* groname: the group name. This a char16 and should be purely <UL>
alphanumeric. Do not include underscores or other punctuation. <LI> groname: the group name. This a char16 and should
* grosysid: the group id. This is an int4. This should be unique for be purely alphanumeric. Do not include underscores
each group. or other punctuation.
* grolist: the list of pg_user id's that belong in the group. This <LI> grosysid: the group id. This is an int4.
is an int4[]. This should be unique for each group.
<LI> grolist: the list of pg_user id's that belong in the group.
3.10) What is the exact difference between binary cursors and normal cursors? This is an int4[].
</UL>
Normal cursors return data back in ASCII format. Since data is stored <P>
natively in binary format, the system must do a conversion to produce <H3><a name="3.10">3.10</a>) What is the exact difference between binary
the ASCII format. In addition, ASCII formats are often large in size cursors and normal cursors?</H3>
than binary format. Once the attributes come back in ASCII, often the <P>
client application then has to convert it to a binary format to Normal cursors return data back in ASCII format. Since data is stored
manipulate it anyway. natively in binary format, the system must do a conversion to produce
the ASCII format. In addition, ASCII formats are often large in size
Binary cursors give you back the data in the native binary than binary format. Once the attributes come back in ASCII, often the
representation. Thus, binary cursors will tend to be a little faster client application then has to convert it to a binary format to
since there's less overhead of conversion. manipulate it anyway.
<P>
However, ASCII is architectural neutral whereas binary representation Binary cursors give you back the data in the native binary
can differ between different machine architecture. Thus, if your representation. Thus, binary cursors will tend to be a little faster
client machine uses a different representation than you server since there's less overhead of conversion.
machine, getting back attributes in binary format is probably not what <P>
you want. Also, if your main purpose is displaying the data in ASCII, However, ASCII is architectural neutral whereas binary representation
then getting it back in ASCII will save you some effort on the client can differ between different machine architecture. Thus, if your client
side. machine uses a different representation than you server machine, getting
back attributes in binary format is probably not what you want. Also, if
3.11) Why doesn't the != operator work? your main purpose is displaying the data in ASCII, then getting it back
in ASCII will save you some effort on the client side.
SQL specifies <> as the inequality operator, and that is what we have <P>
defined for the built-in types. <H3><a name="3.11">3.11</a>) Why doesn't the != operator work?</H3>
<P>
In 6.0, != is equivalent to <>. SQL specifies &lt;&gt; as the inequality operator, and that is what we
have defined for the built-in types.
3.12) What is a R-tree index and what is it used for? <P>
In 6.0, != is equivalent to &lt;&gt;.
An r-tree index is used for indexing spatial data. A hash index can't <P>
handle range searches. A B-tree index only handles range searches in a <H3><a name="3.12">3.12</a>) What is a R-tree index and what is it used for?</H3>
single dimension. R-tree's can handle multi-dimensional data. For <P>
example, if a R-tree index can be built on an attribute of type An r-tree index is used for indexing spatial data. A hash index can't
'point', the system can more efficient answer queries like select all handle range searches. A B-tree index only handles range searches in a
points within a bounding rectangle. 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 canonical paper that describes the original R-Tree design is: the system can more efficient answer queries like select all points
within a bounding rectangle.
Guttman, A. "R-Trees: A Dynamic Index Structure for Spatial <P>
Searching." Proc of the 1984 ACM SIGMOD Int'l Conf on Mgmt of Data, The canonical paper that describes the original R-Tree design is:
45-57. <P>
Guttman, A. "R-Trees: A Dynamic Index Structure for Spatial Searching."
You can also find this paper in Stonebraker's "Readings in Database Proc of the 1984 ACM SIGMOD Int'l Conf on Mgmt of Data, 45-57.
Systems" <P>
You can also find this paper in Stonebraker's "Readings in Database
3.13) What is the maximum size for a tuple? Systems"
<P>
Tuples are limited to 8K bytes. Taking into account system attributes <H3><a name="3.13">3.13</a>) What is the maximum size for a tuple?</H3>
and other overhead, one should stay well shy of 8,000 bytes to be on <P>
the safe side. To use attributes larger than 8K, try using the large Tuples are limited to 8K bytes. Taking into account system attributes
objects interface. 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
Tuples do not cross 8k boundaries so a 5k tuple will require 8k of objects interface.
storage. <P>
Tuples do not cross 8k boundaries so a 5k tuple will require 8k of
3.14) I defined indices but my queries don't seem to make use of them. Why? storage.
<P>
PostgreSQL does not automatically maintain statistics. One has to make <H3><a name="3.14">3.14</a>) I defined indices but my queries don't seem
an explicit 'vacuum' call to update the statistics. After statistics to make use of them. Why?</H3>
are updated, the optimizer has a better shot at using indices. Note <P>
that the optimizer is limited and does not use indices in some PostgreSQL does not automatically maintain statistics. One has to make
circumstances (such as OR clauses). an explicit 'vacuum' call to update the statistics. After statistics
are updated, the optimizer has a better shot at using indices. Note
If the system still does not see the index, it is probably because you that the optimizer is limited and does not use indices in some
have created an index on a field with the improper *_ops type. For circumstances (such as OR clauses).
example, you have created a CHAR(4) field, but have specified a <P>
char_ops index type_class. 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
See the create_index manual page for information on what type classes example, you have created a CHAR(4) field, but have specified a char_ops
are available. It must match the field type. index type_class.
<P>
Postgres does not warn the user when the improper index is created. See the create_index manual page for information on what type classes
are available. It must match the field type.
Indexes not used for ORDER BY operations. <P>
Postgres does not warn the user when the improper index is created.
3.15) Are there ODBC drivers for PostgreSQL? <P>
Indexes not used for ORDER BY operations.
There are two ODBC drivers available, PostODBC and OpenLink ODBC. <P>
<H3><a name="3.15">3.15</a>) Are there ODBC drivers for PostgreSQL?</H3>
For all people being interested in PostODBC, there are now two mailing <P>
lists devoted to the discussion of PostODBC. The mailing lists are: There are two ODBC drivers available, PostODBC and OpenLink ODBC.
* postodbc-users@listserv.direct. net <P>
* postodbc-developers@listse rv.direct.net For all people being interested in PostODBC, there are now two mailing
lists devoted to the discussion of PostODBC. The mailing lists are:
these lists are ordinary majordomo mailing lists. You can subscribe by <UL>
sending a mail to: <LI> <a
* majordomo@listserv.direct.net href="mailto:postodbc-users@listserv.direct.net">postodbc-users@listserv.direct.
net</a>
OpenLink ODBC is currently in beta under Linux. You can get it from <LI> <a
http://www.openlinksw.com/postgres.html. It works with our standard href="mailto:postodbc-developers@listserv.direct.net">postodbc-developers@listse
ODBC client software so you'll have Postgres ODBC available on every rv.direct.net</a>
client platform we support (Win, Mac, Unix, VMS). </UL>
<P>
We will probably be selling this product to people who need these lists are ordinary majordomo mailing lists. You can subscribe by
commercial-quality support, but a freeware version will always be sending a mail to:
available. Questions to postgres95@openlink.co.uk. <UL>
<LI> <a
3.16) How do I use postgres for multi-dimensional indexing (> 2 dimensions)? href="mailto:majordomo@listserv.direct.net">majordomo@listserv.direct.net</a>
</UL>
Builtin R-Trees can handle polygons and boxes. In theory, R-trees can <P>
be extended to handle higher number of dimensions. In practice, OpenLink ODBC is currently in beta under Linux. You can get it from <a
extending R-trees require a bit of work and we don't currently have href="http://www.openlinksw.com/postgres.html">
any documentation on how to do it. http://www.openlinksw.com/postgres.html</a>. It works with our standard
ODBC client software so you'll have Postgres ODBC available on every
3.17) How do I do regular expression searches? case-insensitive regexp client platform we support (Win, Mac, Unix, VMS).
searching? <P>
We will probably be selling this product to people who need
PostgreSQL supports the SQL LIKE syntax as well as more general commercial-quality support, but a freeware version will always be
regular expression searching with the ~ operator. The !~ is the available. Questions to <a
negated regexp operator. ~* and !~* are the case-insensitive regular href="mailto:postgres95@openlink.co.uk">postgres95@openlink.co.uk</a>.
expression operators. <P>
<H3><a name="3.16">3.16</a>) How do I use postgres for multi-dimensional
3.18) I can't access the database as the 'root' user. indexing (&gt; 2 dimensions)?</H3>
<P>
You should not create database users with user id 0(root). They will Builtin R-Trees can handle polygons and boxes. In theory, R-trees can
be unable to access the database. This is a security precaution be extended to handle higher number of dimensions. In practice,
because of the ability of any user to dynamically link object modules extending R-trees require a bit of work and we don't currently have any
into the database engine. documentation on how to do it.
<P>
3.19) I experienced a server crash during a vacuum. How do I remove the lock <H3><a name="3.17">3.17</a>) How do I do regular expression searches?
file? case-insensitive regexp searching?</H3>
<P>
If the server crashes during a vacuum command, chances are it will PostgreSQL supports the SQL LIKE syntax as well as more general regular
leave a lock file hanging around. Attempts to re-run the vacuum expression searching with the ~ operator. The !~ is the negated regexp
command result in operator. ~* and !~* are the case-insensitive regular expression
operators.
<P>
<H3><a name="3.18">3.18</a>) I can't access the database as the 'root' user.</H3>
<P>
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.
<P>
<H3><a name="3.19">3.19</a>) I experienced a server crash during a
vacuum. How do I remove the lock file?</H3>
<P>
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
<PRE>
<SAMP>
WARN:can't create lock file -- another vacuum cleaner running? WARN:can't create lock file -- another vacuum cleaner running?
</SAMP>
If you are sure that no vacuum is actually running, you can remove the </PRE>
file called "pg_vlock" in your database directory (which is <P>
$PGDATA/base/<dbName>) If you are sure that no vacuum is actually running, you can remove the
file called "pg_vlock" in your database directory (which is
3.20) What is the difference between the various character types? $PGDATA/base/&lt;dbName&gt;)
<P>
<H3><a name="3.20">3.20</a>) What is the difference between the various
character types?</H3>
<PRE>
Type Internal Name Notes Type Internal Name Notes
-------------------------------------------------- --------------------------------------------------
CHAR char 1 character } CHAR char 1 character }
...@@ -592,343 +676,368 @@ CHAR(#) bpchar blank padded to the specified fixed length ...@@ -592,343 +676,368 @@ CHAR(#) bpchar blank padded to the specified fixed length
VARCHAR(#) varchar size specifies maximum length, no padding VARCHAR(#) varchar size specifies maximum length, no padding
TEXT text length limited only by maximum tuple length TEXT text length limited only by maximum tuple length
BYTEA bytea variable-length array of bytes BYTEA bytea variable-length array of bytes
</PRE>
Remember, you need to use the internal name when creating indexes on <P>
these fields or when doing other internal operations. 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 <P>
bytes is the length, followed by the data). CHAR(#) and VARCHAR(#) The last four types above are "varlena" types (i.e. the first four bytes
allocate the maximum number of bytes no matter how much data is stored is the length, followed by the data). CHAR(#) and VARCHAR(#) allocate
in the field. TEXT and BYTEA are the only character types that have the maximum number of bytes no matter how much data is stored in the
variable length on the disk. 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? <P>
<H3><a name="3.21">3.21</a>) In a query, how do I detect if a field is NULL?</H3>
PostgreSQL has two builtin keywords, "isnull" and "notnull" (note no <P>
spaces). Version 1.05 and later and 6.* understand IS NULL and IS NOT PostgreSQL has two builtin keywords, "isnull" and "notnull" (note no
NULL. spaces). Version 1.05 and later and 6.* understand IS NULL and IS NOT
NULL.
3.22) How do I see how the query optimizer is evaluating my query? <P>
<H3><a name="3.22">3.22</a>) How do I see how the query optimizer is
Place the word 'EXPLAIN' at the beginning of the query, for example: evaluating my query?</H3>
<P>
Place the word 'EXPLAIN' at the beginning of the query, for example:
<PRE>
<CODE>
EXPLAIN SELECT * FROM table1 WHERE age = 23; EXPLAIN SELECT * FROM table1 WHERE age = 23;
</CODE>
3.23) How do I create a serial field? </PRE>
<P>
Postgres does not allow the user to specifiy a user column as type <H3><a name="3.23">3.23</a>) How do I create a serial field?</H3>
SERIAL. Instead, you can use each row's oid field as a unique value. <P>
However, if you need to dump and reload the database, you need to be Postgres does not allow the user to specifiy a user column as type
using postgres version 1.07 or later or 6.* with pgdump's -o option or SERIAL. Instead, you can use each row's oid field as a unique value.
COPY's WITH OIDS option to preserver the oids. However, if you need to dump and reload the database, you need to be
using postgres version 1.07 or later or 6.* with pgdump's -o option or
Another valid way of doing this is to create a function: COPY's WITH OIDS option to preserver the oids.
<P>
Another valid way of doing this is to create a function:
<PRE>
<CODE>
create table my_oids (f1 int4); create table my_oids (f1 int4);
insert into my_oids values (1); insert into my_oids values (1);
create function new_oid () returns int4 as create function new_oid () returns int4 as
'update my_oids set f1 = f1 + 1; select f1 from my_oids; ' 'update my_oids set f1 = f1 + 1; select f1 from my_oids; '
language 'sql'; language 'sql';
</CODE>
then: </PRE>
<P>
then:
<PRE>
<CODE>
create table my_stuff (my_key int4, value text); create table my_stuff (my_key int4, value text);
insert into my_stuff values (new_oid(), 'hello'); insert into my_stuff values (new_oid(), 'hello');
</CODE>
However, keep in mind there is a race condition here where one server </PRE>
could do the update, then another one do an update, and they both <P>
could select the same new id. This statement should be performed However, keep in mind there is a race condition here where one server
within a transaction. 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
3.24) How do I create a multi-column index? transaction.
<P>
In 6.0, you can not directly create a multi-column index using create Sequences are implemented in 6.1
index. You need to define a function which acts on the multiple <P>
columns, then use create index with that function. <H3><a name="3.24">3.24</a>) How do I create a multi-column index?</H3>
<P>
In 6.1, this feature is available.
In 6.0, you can not directly create a multi-column index using create
3.25) What are the temp_XXX files in my database directory? index. You need to define a function which acts on the multiple columns,
then use create index with that function.
They are temp_ files generated by the query executor. For example, if <P>
a sort needs to be done to satisfy an ORDER BY, some temp files are In 6.1, this feature is available.
generated as a result of the sort. <P>
<H3><a name="3.25">3.25</a>) What are the temp_XXX files in my database
If you have no transactions or sorts running at the time, it is safe directory?</H3>
to delete the temp_ files. <P>
They are temp_ files generated by the query executor. For example, if a
3.26) Why are my table files not getting any smaller after a delete? sort needs to be done to satisfy an ORDER BY, some temp files are
generated as a result of the sort.
If you run vacuum in pre-6.0, unused rows will be marked for reuse, <P>
but the file blocks are not released. If you have no transactions or sorts running at the time, it is safe to
delete the temp_ files.
In 6.0, vacuum properly shrinks tables. <P>
<H3><a name="3.26">3.26</a>) Why are my table files not getting any
3.27) Why can't I connect to my database from another machine? smaller after a delete?</H3>
<P>
The default configuration allows only connections from tcp/ip host If you run vacuum in pre-6.0, unused rows will be marked for reuse, but
localhost. You need to add a host entry to the file pgsql/data/pg_hba. the file blocks are not released.
<P>
3.28) I get the error 'default index class unsupported' when creating an In 6.0, vacuum properly shrinks tables.
index. How do I do it? <P>
<H3><a name="3.27">3.27</a>) Why can't I connect to my database from
You probably used: another machine?</H3>
<P>
The default configuration allows only connections from tcp/ip host
localhost. You need to add a host entry to the file pgsql/data/pg_hba.
<P>
<H3><a name="3.28">3.28</a>) I get the error 'default index class
unsupported' when creating an index. How do I do it?</H3>
<P>
You probably used:
<PRE>
<CODE>
create index idx1 on person using btree (name); create index idx1 on person using btree (name);
</CODE>
PostgreSQL indexes are extensible, and therefore in pre-6.0, you must </PRE>
specify a class_type when creating an index. Read the manual page for <P>
create index (called create_index). PostgreSQL indexes are extensible, and therefore in pre-6.0, you must
specify a class_type when creating an index. Read the manual page for
Version 6.0, if you do not specify a class_type, it defaults to the create index (called create_index).
proper type for the column. <P>
Version 6.0, if you do not specify a class_type, it defaults to the
3.29) Why does creating an index crash the backend server? proper type for the column.
<P>
You have probably defined an incorrect *_ops type class for the field <H3><a name="3.29">3.29</a>) Why does creating an index crash the
you are indexing. backend server?</H3>
<P>
3.30) How do I specify a decimal constant as a float8, or a string as a text? You have probably defined an incorrect *_ops type class for the field
Why am I getting poor precision? you are indexing.
<P>
Use the :: operator. It is needed only when the default promotion <H3><a name="3.30">3.30</a>) How do I find out what indexes or
rules fail. i.e.: operations are defined in the database?</H3>
<P>
Run the file pgsql/src/tutorial/syscat.source. It illustrates many of
insert into tab1 values (4.23::float8, '2343'::text) the 'select's needed to get information out of the database system
tables.
The default floating-point constant is a float4 in releases prior to <P>
1.05. Later releases default to float8. <H3><a name="3.31">3.31</a>) Why do statements require an extra character at
the end? Why does 'createuser' return 'unexpected last match in input()'?
3.31) How do I find out what indexes or operations are defined in the Why does pg_dump fail?</H3>
database? <P>
You have compile postgres with flex version 2.5.3. There is bug in this
Run the file pgsql/src/tutorial/syscat.source. It illustrates many of version of flex. Use flex version 2.5.2 or flex 2.5.4 instead. There
the 'select's needed to get information out of the database system is a doc/README.flex file which will properly patch the flex 2.5.3
tables. source code.
<P>
3.32) My database is corrupt. I can't do anything. What should I do? <H3><a name="3.32">3.32</a>) All my servers crash under concurrent table
access. Why?</H3>
The 1.02 release has a README file and utility that describes a <P>
possible cause of the problem and a workaround. This problem can be caused by a kernel that is not configured to support
semaphores.
This bug is fixed in 1.02.1. <P>
<H3><a name="3.33">3.33</a>) What tools are available for hooking
3.33) Createdb, destroydb, createuser,destroyuser don't run. Why? postgres to Web pages?</H3>
<P>
Release 1.02 does not have this problem. For web integration, PHP/FI is an excellent interface. The URL for that
is <a href="http://www.vex.net/php/">http://www.vex.net/php/</a>
The 1.01 release of PostgreSQL uses a variable called PAGER to filter <P>
the output of SELECT statements. Unfortunately, this PAGER is used PHP is great for simple stuff, but for more complex stuff, some still
even when the standard output is not a terminal. use the perl interface and CGI.pm.
<P>
3.34) Why do statements require an extra character at the end? Why does An example of using WWW with C to talk to Postgres is can be tried at:
'createuser' return 'unexpected last match in input()'? Why does pg_dump <UL>
fail? <LI>
<a href="http://postgreSQL.org/%7Emlc">http://postgreSQL.org/~mlc</a>
You have compile postgres with flex version 2.5.3. There is bug in </UL>
this version of flex. Use flex version 2.5.2 or flex 2.5.4 instead. <P>
There is a doc/README.flex file which will properly patch the flex An WWW gatway based on WDB using perl can be downloaded from:
2.5.3 source code. <UL>
<LI>
3.35) All my servers crash under concurrent table access. Why? <a
href="http://www.eol.ists.ca/~dunlop/wdb-p95">http://www.eol.ists.ca/~dunlop/wdb
This problem can be caused by a kernel that is not configured to -p95</a>
support semaphores. </UL>
<H3><a name="3.34">3.34</a>) What is the time-warp feature and how does
3.36) What tools are available for hooking postgres to Web pages? it relate to vacuum?</H3>
<P>
For web integration, PHP/FI is an excellent interface. The URL for PostgreSQL handles data changes differently than most database systems.
that is http://www.vex.net/php/ 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
PHP is great for simple stuff, but for more complex stuff, some still default, only current rows are used in a table. If you specify a
use the perl interface and CGI.pm. date/time after the table name in a FROM clause, you can access the data
that was current at that time, i.e.
An example of using WWW with C to talk to Postgres is can be tried at: <PRE>
* http://postgreSQL.org/~mlc <CODE>
An WWW gatway based on WDB using perl can be downloaded from:
* http://www.eol.ists.ca/~dunlop/wdb -p95
3.37) What is the time-warp feature and how does it relate to vacuum?
PostgreSQL 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 * SELECT *
FROM employees ['July 24, 1996 09:00:00'] FROM employees ['July 24, 1996 09:00:00']
</CODE>
displays employee rows in the table at the specified time. You can </PRE>
specify intervals like [date,date], [date,], [,date], or [,]. This <P>
last option accesses all rows that ever existed. displays employee rows in the table at the specified time. You can
specify intervals like [date,date], [date,], [,date], or [,]. This last
INSERTed rows get a timestamp too, so rows that were not in the table option accesses all rows that ever existed.
at the desired time will not appear. <P>
INSERTed rows get a timestamp too, so rows that were not in the table at
Vacuum removes rows that are no longer current. This time-warp feature the desired time will not appear.
is used by the engine for rollback and crash recovery. Expiration <P>
times can be set with purge. Vacuum removes rows that are no longer current. This time-warp feature
is used by the engine for rollback and crash recovery. Expiration times
In 6.0, once a table is vacuumed, the creation time of a row may be can be set with purge.
incorrect, causing time-traval to fail. <P>
In 6.0, once a table is vacuumed, the creation time of a row may be
The time-travel feature will be removed in 7.0. incorrect, causing time-traval to fail.
<P>
3.38) How do I tune the database engine for better performance? The time-travel feature will be removed in 7.0.
<P>
There are two things that can be done. You can use Openlink's option <H3><a name="3.35">3.35</a>) How do I tune the database engine for
to disable fsync() by starting the postmaster with a '-o -F' option. better performance?</H3>
This will prevent fsync()'s from flushing to disk after every <P>
transaction. 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
You can also use the postmaster -B option to increase the number of will prevent fsync()'s from flushing to disk after every transaction.
shared memory buffers shared among the backend processes. If you make <P>
this parameter too high, the process will not start or crash You can also use the postmaster -B option to increase the number of
unexpectedly. Each buffer is 8K and the defualt is 64 buffers. shared memory buffers shared among the backend processes. If you make
this parameter too high, the process will not start or crash
3.39) What debugging features are available in PostgreSQL? unexpectedly. Each buffer is 8K and the defualt is 64 buffers.
<P>
PostgreSQL has several features that report status information that <H3><a name="3.36">3.36</a>) What debugging features are available in
can be valuable for debugging purposes. PostgreSQL?</H3>
<P>
First, by compiling with DEBUG defined, many assert()'s monitor the PostgreSQL has several features that report status information that can
progress of the backend and halt the program when something unexpected be valuable for debugging purposes.
occurs. <P>
First, by compiling with DEBUG defined, many assert()'s monitor the
Both postmaster and postgres have several debug options available. progress of the backend and halt the program when something unexpected
First, whenever you start the postmaster, make sure you send the occurs.
standard output and error to a log file, like: <P>
Both postmaster and postgres have several debug options available.
First, whenever you start the postmaster, make sure you send the
standard output and error to a log file, like:
<PRE>
<KBD>
cd /usr/local/pgsql cd /usr/local/pgsql
./bin/postmaster >server.log 2>&1 & ./bin/postmaster &gt;server.log 2&gt;&1 &
</KBD>
This will put a server.log file in the top-level PostgreSQL directory. </PRE>
This file can contain useful information about problems or errors <P>
encountered by the server. Postmaster has a -d option that allows even This will put a server.log file in the top-level PostgreSQL directory.
more detailed information to be reported. The -d option takes a number This file can contain useful information about problems or errors
1-3 that specifies the debug level. The query plans in a verbose debug encountered by the server. Postmaster has a -d option that allows even
file can be formatted using the 'indent' program. (You may need to more detailed information to be reported. The -d option takes a number
remove the '====' lines in 1.* releases.) Be warned that a debug level 1-3 that specifies the debug level. The query plans in a verbose debug
greater than one generates large log files in 1.* releases. file can be formatted using the 'indent' program. (You may need to
remove the '====' lines in 1.* releases.) Be warned that a debug level
You can actuall run the postgres backend from the command line, and greater than one generates large log files in 1.* releases.
type your SQL statement directly. This is recommended ONLY for <P>
debugging purposes. Note that a newline terminates the query, not a You can actuall run the postgres backend from the command line, and type
semicolon. If you have compiled with debugging symbols, you can your SQL statement directly. This is recommended ONLY for debugging
perhaps use a debugger to see what is happening. Because the backend purposes. Note that a newline terminates the query, not a semicolon. If
was not started from the postmaster, it is not running in an identical you have compiled with debugging symbols, you can perhaps use a debugger
environment and locking/backend interaction problems may not be to see what is happening. Because the backend was not started from the
duplicated. Some operating system can attach to a running backend postmaster, it is not running in an identical environment and
directly to diagnose problems. locking/backend interaction problems may not be duplicated. Some
operating system can attach to a running backend directly to diagnose
The postgres program has a -s, -A, -t options that can be very usefull problems.
for debugging and performance measurements. <P>
The postgres program has a -s, -A, -t options that can be very usefull
The EXPLAIN command (see this FAQ) allows you to see how PostgreSQL is for debugging and performance measurements.
iterpreting your query. <P>
The EXPLAIN command (see this FAQ) allows you to see how PostgreSQL is
3.40) What is an oid? What is a tid? iterpreting your query.
<P>
Oids are Postgres's answer to unique row ids or serial columns. Every <H3><a name="3.37">3.37</a>) What is an oid? What is a tid?</H3>
row that is created in Postgres gets a unique oid. All oids generated <P>
by initdb are less than 16384 (from backend/access/transam.h). All Oids are Postgres's answer to unique row ids or serial columns. Every
post-initdb (user-created) oids are equal or greater that this. All row that is created in Postgres gets a unique oid. All oids generated
these oids are unique not only within a table, or database, but unique by initdb are less than 16384 (from backend/access/transam.h). All
within the entire postgres installation. post-initdb (user-created) oids are equal or greater that this. All
these oids are unique not only within a table, or database, but unique
Postgres uses oids in its internal system tables to link rows in within the entire postgres installation.
separate tables. These oids can be used to identify specific user rows <P>
and used in joins. It is recommended you use column type oid to store Postgres uses oids in its internal system tables to link rows in
oid values. See the sql(l) manual page to see the other internal separate tables. These oids can be used to identify specific user rows
columns. and used in joins. It is recommended you use column type oid to store
oid values. See the sql(l) manual page to see the other internal
Tids are used to indentify specific physical rows with block and columns.
offset values. Tids change after rows are modified or reloaded. They <P>
are used by index entries to point to physical rows. They can not be Tids are used to indentify specific physical rows with block and offset
accessed through sql. values. Tids change after rows are modified or reloaded. They are used
by index entries to point to physical rows. They can not be accessed
3.41) What is the meaning of some of the terms used in Postgres? through sql.
<P>
Some of the source code and older documentation use terms that have <H3><a name="3.38">3.38</a>) What is the meaning of some of the terms
more common usage. Here are some: used in Postgres?</H3>
* row, record, tuple <P>
* attribute, field, column Some of the source code and older documentation use terms that have more
* table, class common usage. Here are some:
* retrieve, select <UL>
* replace, update <LI> row, record, tuple
* append, insert <LI> attribute, field, column
* oid, serial value <LI> table, class
* portal, cursor <LI> retrieve, select
* range variable, table name, table alias <LI> replace, update
<LI> append, insert
Please let me know if you think of any more. <LI> oid, serial value
<LI> portal, cursor
3.42) What is Genetic Query Optimization? <LI> range variable, table name, table alias
</UL>
The GEQO module in PostgreSQL is intended to solve the query <P>
optimization problem of joining many tables by means of a Genetic Please let me know if you think of any more.
Algorithm (GA). It allows the handling of large join queries through <P>
non-exhaustive search. <H3><a name="3.39">3.39</a>) What is Genetic Query Optimization?</H3>
<P>
For further information see README.GEQO <utesch@aut.tu-freiberg.de>. The GEQO module in PostgreSQL is intended to solve the query
optimization problem of joining many tables by means of a Genetic
3.43) I am running Solaris and my dates display wrong. Why? Algorithm (GA). It allows the handling of large join queries through
non-exhaustive search.
Gcc under Solaris has an bug when compiled with optimization level 2. <P>
Edit 'configure', and change -O2 to -O, and recompile. If 'configure' For further information see README.GEQO &lt;utesch@aut.tu-freiberg.de&gt;.
does not exist in your top level source directory, make the change to <P>
Makefile.global. <H3><a name="3.40">3.40</a>) I am running Solaris and my dates
display wrong. Why?</H3>
_________________________________________________________________ <P>
There was a bug in 6.0 that caused this problem under Solaris with -O2
Section 4: Extending PostgreSQL optimization.
Upgrade to 6.1.
4.1) I wrote a user-defined function and when I run it in psql, it dumps <P>
core. <H3><a name="3.41">3.41</a>) How do I enable more than 32 concurrent
backends?</H3>
The problem could be a number of things. Try testing your user-defined <P>
function in a stand alone test program first. Also, make sure you are Edit include/storage/sinvaladt.h, and change the value of MaxBackendId.
not sending elog NOTICES when the front-end is expecting data, such as In the future, we plan to make this a configurable prameter.
during a type_in() or type_out() functions <P>
<HR>
4.2) I get messages of the type NOTICE:PortalHeapMemoryFree: 0x402251d0 not <H2> Section 4: Extending PostgreSQL
in alloc set! </H2>
<P>
You are pfree'ing something that was not palloc'ed. When writing <H3><a name="4.1">4.1</a>) I wrote a user-defined function and when I run it
user-defined functions, do not include the file "libpq-fe.h". Doing so in psql, it dumps core.</H3>
will cause your palloc to be a malloc instead of a free. Then, when <P>
the backend pfrees the storage, you get the notice message. 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
4.3) I've written some nifty new types and functions for PostgreSQL. not sending elog NOTICES when the front-end is expecting data, such as
during a type_in() or type_out() functions
Please share them with other PostgreSQL users. Send your extensions to <P>
mailing list, and they will eventually end up in the contrib/ <H3><a name="4.2">4.2</a>) I get messages of the type
subdirectory. NOTICE:PortalHeapMemoryFree: 0x402251d0 not in alloc set!</H3>
<P>
4.4) How do I write a C function to return a tuple? 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
This requires extreme wizardry, so extreme that the authors have not will cause your palloc to be a malloc instead of a free. Then, when the
ever tried it, though in principle it can be done. The short answer is backend pfrees the storage, you get the notice message.
... you can't. This capability is forthcoming in the future. <P>
<H3><a name="4.3">4.3</a>) I've written some nifty new types and functions for
_________________________________________________________________ PostgreSQL.</H3>
<P>
Section 5: Bugs Please share them with other PostgreSQL users. Send your extensions to
mailing list, and they will eventually end up in the contrib/
5.1) How do I make a bug report? subdirectory.
<P>
Check the current FAQ at http://postgreSQL.org <H3><a name="4.4">4.4</a>) How do I write a C function to return a tuple?</H3>
<P>
Also check out our ftp site ftp://ftp.postgreSQL.org/pub to see if This requires extreme wizardry, so extreme that the authors have not
there is a more recent PostgreSQL version. ever tried it, though in principle it can be done. The short answer is
... you can't. This capability is forthcoming in the future.
You can also fill out the "bug-template" file and send it to: <P>
* bugs@postgreSQL.org <HR>
<H2> Section 5: Bugs
This is the address of the developers mailing list. </H2>
<P>
<H3><a name="5.1">5.1</a>) How do I make a bug report?</H3>
<P>
Check the current FAQ at <a
href="http://postgreSQL.org">http://postgreSQL.org</a>
<P>
Also check out our ftp site <a
href="ftp://ftp.postgreSQL.org/pub">ftp://ftp.postgreSQL.org/pub</a> to
see if there is a more recent PostgreSQL version.
<P>
You can also fill out the "bug-template" file and send it to:
<UL>
<LI> <a href="mailto:bugs@postgreSQL.org">bugs@postgreSQL.org</a>
</UL>
<P>
This is the address of the developers mailing list.
</BODY>
</HTML>
doc/TODO
View file @ 9b22846e
...@@ -122,6 +122,8 @@ add pg_type attribute to identify types that need length (bpchar, varchar) ...@@ -122,6 +122,8 @@ add pg_type attribute to identify types that need length (bpchar, varchar)
add UNIQUE capability to non-btree indexes add UNIQUE capability to non-btree indexes
make pg_dumpall preserve table ownership, not just database ownership make pg_dumpall preserve table ownership, not just database ownership
make large objects have their own reltype make large objects have their own reltype
make number of backends a config parameter, storage/sinvaladt.h:MaxBackendId
certain indexes will not shrink, i.e. oid indexes with many inserts
PERFORMANCE PERFORMANCE
----------- -----------
......
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