Frequently Asked Questions (FAQ) for PostgreSQL
- Last updated: Sun Jan 30 21:44:35 EST 2005
+ Last updated: Mon Jan 31 15:40:24 EST 2005
Current maintainer: Bruce Momjian (pgman@candle.pha.pa.us)
By default, PostgreSQL only allows connections from the local machine
using Unix domain sockets or TCP/IP connections. Other machines will
not be able to connect unless you modify listen_addresses in the
- postgresql.conf and enable host-based authentication by modifying the
- file $PGDATA/pg_hba.conf accordingly.
+ postgresql.conf file, enable host-based authentication by modifying
+ the $PGDATA/pg_hba.conf file, and restart the server.
3.3) How do I tune the database engine for better performance?
- Certainly, indexes can speed up queries. The EXPLAIN ANALYZE command
- allows you to see how PostgreSQL is interpreting your query, and which
- indexes are being used.
-
- If you are doing many INSERTs, consider doing them in a large batch
- using the COPY command. This is much faster than individual INSERTS.
- Second, statements not in a BEGIN WORK/COMMIT transaction block are
- considered to be in their own transaction. Consider performing several
- statements in a single transaction block. This reduces the transaction
- overhead. Also, consider dropping and recreating indexes when making
- large data changes.
-
- There are several tuning options in the Administration Guide/Server
- Run-time Environment/Run-time Configuration. You can disable fsync()
- by using fsync option. This will prevent fsync()s from flushing to
- disk after every transaction.
-
- You can use the shared_buffers option to increase the number of shared
- memory buffers used by the backend processes. If you make this
- parameter too high, the postmaster may not start because you have
- exceeded your kernel's limit on shared memory space. Each buffer is 8K
- and the default is 1000 buffers.
-
- You can also use the sort_mem (from PostgreSQL 8.0: work_mem) options
- to increase the maximum amount of memory used by the backend processes
- for each temporary sort. The default is 1024 (i.e. 1MB).
-
- You can also use the CLUSTER command to group data in tables to match
- an index. See the CLUSTER manual page for more details.
+ There are three major areas for potential performance improvement:
+ Query Changes
+ This involves modifying queries to obtain better performance:
+
+ + Creation of indexes, including expression and partial indexes
+ + Use of COPY instead of multiple INSERTs
+ + Grouping of multiple statements into a single transaction to
+ reduce commit overhead
+ + Use of CLUSTER when retrieving many rows from an index
+ + Use of LIMIT for returning a subset of a query's output
+ + Use of Prepared queries
+ + Use of ANALYZE to maintain accurate optimizer statistics
+ + Regular use of VACUUM or pg_autovacuum
+ + Dropping of indexes during large data changes
+
+ Server Configuration
+ A number of postgresql.conf settings affect performance. For
+ more details, see Administration Guide/Server Run-time
+ Environment/Run-time Configuration for a full listing, and for
+ commentary see
+ http://www.varlena.com/varlena/GeneralBits/Tidbits/annotated_co
+ nf_e.html and
+ http://www.varlena.com/varlena/GeneralBits/Tidbits/perf.html.
+
+ Hardware Selection
+ The effect of hardware on performance is detailed in
+ http://candle.pha.pa.us/main/writings/pgsql/hw_performance/inde
+ x.html.
+
3.4) What debugging features are available?
PostgreSQL has several features that report status information that
alink="#0000ff">
<H1>Frequently Asked Questions (FAQ) for PostgreSQL</H1>
- <P>Last updated: Sun Jan 30 21:44:35 EST 2005</P>
+ <P>Last updated: Mon Jan 31 15:40:24 EST 2005</P>
<P>Current maintainer: Bruce Momjian (<A href=
"mailto:pgman@candle.pha.pa.us">pgman@candle.pha.pa.us</A>)
RHDB Admin (<a
href="http://sources.redhat.com/rhdb/">http://sources.redhat.com/rhd
b/ </a>), TORA (<a
- href="http://www.globecom.net/tora/">http://www.globecom.net/tora/</
-
a>, partly commercial), and Rekall (<a
+ href="http://www.globecom.net/tora/">http://www.globecom.net/tora/</a>,
+ partly commercial), and Rekall (<a
href="http://www.rekallrevealed.org/">
http://www.rekallrevealed.org/</a>). There is also PhpPgAdmin (<a
href="http://phppgadmin.sourceforge.net/">
<P>By default, PostgreSQL only allows connections from the local
machine using Unix domain sockets or TCP/IP connections. Other
machines will not be able to connect unless you modify
- listen_addresses in the postgresql.conf <B>and</B> enable
- host-based authentication by modifying the file
- <I>$PGDATA/pg_hba.conf</I> accordingly.</P>
+ <I>listen_addresses</I> in the <I>postgresql.conf</I> file, enable
+ host-based authentication by modifying the
+ <I>$PGDATA/pg_hba.conf</I> file, and restart the server.</P>
<H4><A name="3.3">3.3</A>) How do I tune the database engine for
better performance?</H4>
- <P>Certainly, indexes can speed up queries. The
- <SMALL>EXPLAIN ANALYZE</SMALL> command allows you to see how
- PostgreSQL is interpreting your query, and which indexes are
- being used.</P>
-
- <P>If you are doing many <SMALL>INSERTs</SMALL>, consider doing
- them in a large batch using the <SMALL>COPY</SMALL> command. This
- is much faster than individual <SMALL>INSERTS</SMALL>. Second,
- statements not in a <SMALL>BEGIN WORK/COMMIT</SMALL> transaction
- block are considered to be in their own transaction. Consider
- performing several statements in a single transaction block. This
- reduces the transaction overhead. Also, consider dropping and
- recreating indexes when making large data changes.</P>
-
- <P>There are several tuning options in the <a href=
+ <P>There are three major areas for potential performance
+ improvement:</P>
+
+ <DL>
+ <DT><B>Query Changes</B></DT>
+
+ <DD>This involves modifying queries to obtain better
+ performance:
+ <ul>
+ <li>Creation of indexes, including expression and partial
+ indexes</li>
+ <li>Use of COPY instead of multiple <SMALL>INSERT</SMALL>s</li>
+ <li>Grouping of multiple statements into a single transaction to
+ reduce commit overhead</li>
+ <li>Use of <SMALL>CLUSTER</SMALL> when retrieving many rows from an
+ index</li>
+ <li>Use of <SMALL>LIMIT</SMALL> for returning a subset of a query's
+ output</li>
+ <li>Use of Prepared queries</li>
+ <li>Use of <SMALL>ANALYZE</SMALL> to maintain accurate optimizer
+ statistics</li>
+ <li>Regular use of <SMALL>VACUUM</SMALL> or <I>pg_autovacuum</I>
+ <li>Dropping of indexes during large data changes</li>
+ </ul><BR>
+ <BR>
+ </DD>
+
+ <DT><B>Server Configuration</B></DT>
+
+ <DD>A number of <I>postgresql.conf</I> settings affect performance.
+ For more details, see <a href=
"http://www.postgresql.org/docs/current/static/runtime.html">
- Administration Guide/Server Run-time Environment/Run-time Configuration</a>.
- You can disable <I>fsync()</I> by using <i>fsync</I> option. This will
- prevent <I>fsync()</I>s from flushing to disk after every
- transaction.</P>
-
- <P>You can use the <I>shared_buffers</I> option to
- increase the number of shared memory buffers used by the backend
- processes. If you make this parameter too high, the
- <I>postmaster</I> may not start because you have exceeded your
- kernel's limit on shared memory space. Each buffer is 8K and the
- default is 1000 buffers.</P>
-
- <P>You can also use the <I>sort_mem</I> (from PostgreSQL 8.0: <I>work_mem</I>)
- options to increase the maximum amount of memory used by the backend
- processes for each temporary sort. The default is 1024 (i.e. 1MB).</P>
-
- <P>You can also use the <SMALL>CLUSTER</SMALL> command to group
- data in tables to match an index. See the <SMALL>CLUSTER</SMALL>
- manual page for more details.</P>
+ Administration Guide/Server Run-time Environment/Run-time
+ Configuration</a> for a full listing, and for commentary see <a
+ href="http://www.varlena.com/varlena/GeneralBits/Tidbits/annotated_conf_e.html">
+ http://www.varlena.com/varlena/GeneralBits/Tidbits/annotated_conf_e.html</a>
+ and <a href="http://www.varlena.com/varlena/GeneralBits/Tidbits/perf.html">
+ http://www.varlena.com/varlena/GeneralBits/Tidbits/perf.html</a>.
+ <BR>
+ <BR>
+ </DD>
+
+ <DT><B>Hardware Selection</B></DT>
+
+ <DD>The effect of hardware on performance is detailed in <a
+ href="http://candle.pha.pa.us/main/writings/pgsql/hw_performance/index.html">
+ http://candle.pha.pa.us/main/writings/pgsql/hw_performance/index.html</a>.
+ <BR>
+ <BR>
+ </DD>
+ </DL>
<H4><A name="3.4">3.4</A>) What debugging features are
available?</H4>
compiler compute the dependencies automatically.</P>
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