Frequently Asked Questions (FAQ) for PostgreSQL

Last updated: Sat Apr 2311:22:46 EDT 2005

Last updated: Sat Apr 2314:56:41 EDT 2005

Current maintainer: Bruce Momjian (pgman@candle.pha.pa.us)

PostgreSQL. The platforms that had received explicit testing at the

time of release are listed in the installation instructions.

Starting with version 8.0,PostgreSQLnow runs natively on Microsoft

Windows NT-based operatingsystems like Win2000, WinXP, and Win2003. A

prepackaged installer isavailable at

http://pgfoundry.org/projects/pginstaller. MSDOS-basedversions of

Windows (Win95, Win98, WinMe) can run PostgreSQL usingCygwin.

PostgreSQLalso runs natively on Microsoft Windows NT-based operating

systems like Win2000, WinXP, and Win2003. A prepackaged installer is

available at http://pgfoundry.org/projects/pginstaller. MSDOS-based

versions of Windows (Win95, Win98, WinMe) can run PostgreSQL using

Cygwin.

There is also a Novell Netware 6 port at http://forge.novell.com, and

an OS/2 (eComStation) version at

1.4) Where can I get PostgreSQL?

The primary anonymous ftp site for PostgreSQL is

ftp://ftp.PostgreSQL.org/pub/. For mirror sites, see our main web

site.

Via web browser, use http://www.postgresql.org/ftp/, and via ftp, use

ftp://ftp.PostgreSQL.org/pub/.

1.5) Where can I get support?

The major IRC channel is #postgresql on Freenode (irc.freenode.net).

To connect you can use the Unix program irc -c '#postgresql' "$USER"

irc.freenode.net or use any of the other popular IRC clients. A

Spanish one also exists on the same network, (#postgresql-es), and a

French one, (#postgresqlfr). There is also a PostgreSQL channel on

EFNet.

irc.freenode.net or use any other IRC clients. A Spanish one also

exists on the same network, (#postgresql-es), and a French one,

(#postgresqlfr). There is also a PostgreSQL channel on EFNet.

A list of commercial support companies is available at

http://techdocs.postgresql.org/companies.php.

The latest release of PostgreSQL is version 8.0.2.

We plan to have major releases every ten to twelve months.

We plan to have a major release every year, with minor releases every

few months.

1.8) What documentation is available?

1.10) How can I learn SQL?

The PostgreSQL book at

http://www.postgresql.org/docs/books/awbook.html teaches SQL. There is

another PostgreSQL book at http://www.commandprompt.com/ppbook. There

is a nice tutorial at

http://www.intermedia.net/support/sql/sqltut.shtm, at

http://ourworld.compuserve.com/homepages/graeme_birchall/HTM_COOK.HTM,

and at http://sqlcourse.com.

Another one is "Teach Yourself SQL in 21 Days, Second Edition" at

First, consider the PostgreSQL-specific books mentioned above. Another

one is "Teach Yourself SQL in 21 Days, Second Edition" at

http://members.tripod.com/er4ebus/sql/index.htm

Many of our users like The Practical SQL Handbook, Bowman, Judith S.,

et al., Addison-Wesley. Others like The Complete Reference SQL, Groff

et al., McGraw-Hill.

et al., McGraw-Hill. There is also a nice tutorial at

http://www.intermedia.net/support/sql/sqltut.shtm, at

http://ourworld.compuserve.com/homepages/graeme_birchall/HTM_COOK.HTM,

and at http://sqlcourse.com.

1.11) How do I join the development team?

First, download the latest source and read the PostgreSQL Developers

FAQ and documentation on our web site, or in the distribution. Second,

subscribe to the pgsql-hackers and pgsql-patches mailing lists. Third,

submit high quality patches to pgsql-patches.

There are about a dozen people who have commit privileges to the

PostgreSQL CVS archive. They each have submitted so many high-quality

patches that it was impossible for the existing committers to keep up,

and we had confidence that patches they committed were of high

quality.

See the Developer's FAQ.

1.12) How does PostgreSQL compare to other DBMSs?

Performance

PostgreSQL's performance is comparable to other commercial and

open source databases. It is faster for some things, slower for

others. In comparison to MySQL or leaner database systems, we

are faster for multiple users, complex queries, and a

read/write query load. MySQL is faster for simple SELECT

queries done by a few users. Of course, MySQL does not have

most of the features mentioned in the Features section above.

We are built for reliability and features, and we continue to

improve performance in every release.

others. Our performance is usually +/-10% compared to other

databases.

Reliability

We realize that a DBMS must be reliable, or it is worthless. We

2.3) Does PostgreSQL have a graphical user interface?

Yes, there are several graphical interfaces to PostgreSQL available.

These include pgAdmin III (http://www.pgadmin.org, PgAccess

http://www.pgaccess.org), RHDB Admin (http://sources.redhat.com/rhdb/

), TORA ( http://www.globecom.net/tora/, partly commercial), and

Rekall ( http://www.rekallrevealed.org/). There is also PhpPgAdmin (

http://phppgadmin.sourceforge.net/ ), a web-based interface to

PostgreSQL.

See http://techdocs.postgresql.org/guides/GUITools for a more detailed

Yes, see http://techdocs.postgresql.org/guides/GUITools for a detailed

list.

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printing of query and process statistics which can be very useful for

debugging and performance measurements.

The following detailed debug instructions are to be used to provide

more detailed information for server developers debugging a problem.

It is also possible to debug the server if it isn't operating

properly. First, by running configure with the --enable-cassert

option, many assert()s monitor the progress of the backend and halt

the program when something unexpected occurs.

The postmaster has a -d option that allows even more detailed

information to be reported. The -d option takes a number that

specifies the debug level. Be warned that high debug level values

generate large log files.

If postmaster is not running, you can actually run the postgres

backend from the command line, and type your SQL statement directly.

This is recommended only for debugging purposes. Note that a newline

terminates the query, not a semicolon. If you have compiled with

debugging symbols, you can use a debugger to see what is happening.

Because the backend was not started from postmaster, it is not running

in an identical environment and locking/backend interaction problems

may not be duplicated.

If postmaster is running, start psql in one window, then find the PID

of the postgres process used by psql using SELECT pg_backend_pid().

Use a debugger to attach to the postgres PID. You can set breakpoints

in the debugger and issue queries from psql. If you are debugging

postgres startup, you can set PGOPTIONS="-W n", then start psql. This

will cause startup to delay for n seconds so you can attach to the

process with the debugger, set any breakpoints, and continue through

the startup sequence.

You can also compile with profiling to see what functions are taking

execution time. The backend profile files will be deposited in the

pgsql/data/base/dbname directory. The client profile file will be put

in the client's current directory. Linux requires a compile with

-DLINUX_PROFILE for proper profiling.

3.5) Why do I get "Sorry, too many clients" when trying to connect?

You have reached the default limit is 100 database sessions. You need

PostgreSQL releases?

The PostgreSQL team makes only small changes between minor releases,

so upgrading from 7.4 to 7.4.1 does not require a dump and restore.

so upgrading from 7.4.0 to 7.4.1 does not require a dump and restore.

However, major releases (e.g. from 7.3 to 7.4) often change the

internal format of system tables and data files. These changes are

often complex, so we don't maintain backward compatibility for data

4.6) Why are my queries slow? Why don't they use my indexes?

Indexes are notautomaticallyused by every query. Indexes are only

used if thetable is larger than a minimum size, and the query selects

only asmall percentage of the rows in the table. This is because the

randomdisk access caused by an index scan can be slower than a

straight readthrough the table, or sequential scan.

Indexes are not used by every query. Indexes areusedonly if the

table is larger than a minimum size, and the query selects only a

small percentage of the rows in the table. This is because the random

disk access caused by an index scan can be slower than a straight read

through the table, or sequential scan.

To determine if an index should be used, PostgreSQL must have

statistics about the table. These statistics are collected using