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Add contrib/pg_stat_statements for server-wide tracking of statement execution
statistics. Takahiro Itagaki
This commit is contained in:
Tom Lane
@ -1,4 +1,4 @@
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<!-- $PostgreSQL: pgsql/doc/src/sgml/contrib.sgml,v 1.10 2008/11/19 02:59:28 tgl Exp $ -->
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<!-- $PostgreSQL: pgsql/doc/src/sgml/contrib.sgml,v 1.11 2009/01/04 22:19:59 tgl Exp $ -->
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<appendix id="contrib">
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<title>Additional Supplied Modules</title>
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@ -103,6 +103,7 @@ psql -d dbname -f <replaceable>SHAREDIR</>/contrib/<replaceable>module</>.sql
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&pgfreespacemap;
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&pgrowlocks;
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&pgstandby;
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&pgstatstatements;
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&pgstattuple;
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&pgtrgm;
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&seg;
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@ -1,4 +1,4 @@
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<!-- $PostgreSQL: pgsql/doc/src/sgml/filelist.sgml,v 1.58 2008/11/19 02:59:28 tgl Exp $ -->
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<!-- $PostgreSQL: pgsql/doc/src/sgml/filelist.sgml,v 1.59 2009/01/04 22:19:59 tgl Exp $ -->
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<!entity history SYSTEM "history.sgml">
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<!entity info SYSTEM "info.sgml">
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@ -116,6 +116,7 @@
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<!entity pgfreespacemap SYSTEM "pgfreespacemap.sgml">
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<!entity pgrowlocks SYSTEM "pgrowlocks.sgml">
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<!entity pgstandby SYSTEM "pgstandby.sgml">
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<!entity pgstatstatements SYSTEM "pgstatstatements.sgml">
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<!entity pgstattuple SYSTEM "pgstattuple.sgml">
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<!entity pgtrgm SYSTEM "pgtrgm.sgml">
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<!entity seg SYSTEM "seg.sgml">
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265
doc/src/sgml/pgstatstatements.sgml
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265
doc/src/sgml/pgstatstatements.sgml
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@ -0,0 +1,265 @@
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<!-- $PostgreSQL: pgsql/doc/src/sgml/pgstatstatements.sgml,v 1.1 2009/01/04 22:19:59 tgl Exp $ -->
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<sect1 id="pgstatstatements">
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<title>pg_stat_statements</title>
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<indexterm zone="pgstatstatements">
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<primary>pg_stat_statements</primary>
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</indexterm>
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<para>
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The <filename>pg_stat_statements</filename> module provides a means for
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tracking execution statistics of all SQL statements executed by a server.
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</para>
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<para>
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The module must be loaded by adding <literal>pg_stat_statements</> to
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<xref linkend="guc-shared-preload-libraries"> in
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<filename>postgresql.conf</>, because it requires additional shared memory.
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This means that a server restart is needed to add or remove the module.
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</para>
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<sect2>
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<title>The <structname>pg_stat_statements</structname> view</title>
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<para>
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The statistics gathered by the module are made available via a system view
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named <structname>pg_stat_statements</>. This view contains one row for
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each distinct query text, database ID, and user ID (up to the maximum
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number of distinct statements that the module can track). The columns
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of the view are:
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</para>
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<table>
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<title><structname>pg_stat_statements</> columns</title>
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<tgroup cols="4">
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<thead>
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<row>
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<entry>Name</entry>
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<entry>Type</entry>
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<entry>References</entry>
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<entry>Description</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry><structfield>userid</structfield></entry>
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<entry><type>oid</type></entry>
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<entry><literal><link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.oid</literal></entry>
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<entry>OID of user who executed the statement</entry>
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</row>
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<row>
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<entry><structfield>dbid</structfield></entry>
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<entry><type>oid</type></entry>
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<entry><literal><link linkend="catalog-pg-database"><structname>pg_database</structname></link>.oid</literal></entry>
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<entry>OID of database in which the statement was executed</entry>
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</row>
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<row>
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<entry><structfield>query</structfield></entry>
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<entry><type>text</type></entry>
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<entry></entry>
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<entry>Text of the statement (up to <xref linkend="guc-track-activity-query-size"> bytes)</entry>
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</row>
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<row>
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<entry><structfield>calls</structfield></entry>
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<entry><type>bigint</type></entry>
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<entry></entry>
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<entry>Number of times executed</entry>
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</row>
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<row>
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<entry><structfield>total_time</structfield></entry>
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<entry><type>double precision</type></entry>
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<entry></entry>
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<entry>Total time spent in the statement, in seconds</entry>
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</row>
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<row>
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<entry><structfield>rows</structfield></entry>
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<entry><type>bigint</type></entry>
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<entry></entry>
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<entry>Total number of rows retrieved or affected by the statement</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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<para>
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This view, and the function <function>pg_stat_statements_reset</>,
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are available only in databases they have been specifically installed into
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by running the <filename>pg_stat_statements.sql</> install script.
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However, statistics are tracked across all databases of the server
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whenever the <filename>pg_stat_statements</filename> module is loaded
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into the server, regardless of presence of the view.
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</para>
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<para>
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For security reasons, non-superusers are not allowed to see the text of
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queries executed by other users. They can see the statistics, however,
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if the view has been installed in their database.
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</para>
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<para>
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Note that statements are considered the same if they have the same text,
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regardless of the values of any out-of-line parameters used in the
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statement. Using out-of-line parameters will help to group statements
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together and may make the statistics more useful.
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</para>
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</sect2>
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<sect2>
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<title>Functions</title>
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<variablelist>
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<varlistentry>
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<term>
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<function>pg_stat_statements_reset() returns void</function>
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</term>
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<listitem>
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<para>
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<function>pg_stat_statements_reset</function> discards all statistics
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gathered so far by <filename>pg_stat_statements</>.
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By default, this function can only be executed by superusers.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</sect2>
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<sect2>
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<title>Configuration parameters</title>
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<variablelist>
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<varlistentry>
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<term>
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<varname>pg_stat_statements.max</varname> (<type>integer</type>)
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</term>
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<listitem>
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<para>
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<varname>pg_stat_statements.max</varname> is the maximum number of
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statements tracked by the module (i.e., the maximum number of rows
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in the <structname>pg_stat_statements</> view). If more distinct
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statements than that are observed, information about the least-executed
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statements is discarded.
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The default value is 1000.
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This parameter can only be set at server start.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<varname>pg_stat_statements.track</varname> (<type>enum</type>)
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</term>
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<listitem>
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<para>
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<varname>pg_stat_statements.track</varname> controls which statements
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are counted by the module.
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Specify <literal>top</> to track top-level statements (those issued
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directly by clients), <literal>all</> to also track nested statements
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(such as statements invoked within functions), or <literal>none</> to
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disable.
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The default value is <literal>top</>.
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Only superusers can change this setting.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<varname>pg_stat_statements.save</varname> (<type>boolean</type>)
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</term>
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<listitem>
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<para>
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<varname>pg_stat_statements.save</varname> specifies whether to
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save statement statistics across server shutdowns.
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If it is <literal>off</> then statistics are not saved at
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shutdown nor reloaded at server start.
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The default value is <literal>on</>.
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This parameter can only be set in the <filename>postgresql.conf</>
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file or on the server command line.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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<para>
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The module requires additional shared memory amounting to about
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<varname>pg_stat_statements.max</varname> <literal>*</>
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<xref linkend="guc-track-activity-query-size"> bytes. Note that this
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memory is consumed whenever the module is loaded, even if
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<varname>pg_stat_statements.track</> is set to <literal>none</>.
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</para>
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<para>
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In order to set any of these parameters in your
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<filename>postgresql.conf</> file,
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you will need to add <literal>pg_stat_statements</> to
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<xref linkend="guc-custom-variable-classes">. Typical usage might be:
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</para>
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<programlisting>
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# postgresql.conf
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shared_preload_libraries = 'pg_stat_statements'
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custom_variable_classes = 'pg_stat_statements'
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pg_stat_statements.max = 10000
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pg_stat_statements.track = all
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</programlisting>
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</sect2>
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<sect2>
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<title>Sample output</title>
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<programlisting>
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$ pgbench -i bench
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postgres=# SELECT pg_stat_statements_reset();
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$ pgbench -c10 -t300 -M prepared bench
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postgres=# \x
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postgres=# SELECT * FROM pg_stat_statements ORDER BY total_time DESC LIMIT 3;
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-[ RECORD 1 ]------------------------------------------------------------
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userid | 10
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dbid | 63781
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query | UPDATE branches SET bbalance = bbalance + $1 WHERE bid = $2;
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calls | 3000
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total_time | 20.716706
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rows | 3000
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-[ RECORD 2 ]------------------------------------------------------------
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userid | 10
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dbid | 63781
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query | UPDATE tellers SET tbalance = tbalance + $1 WHERE tid = $2;
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calls | 3000
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total_time | 17.1107649999999
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rows | 3000
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-[ RECORD 3 ]------------------------------------------------------------
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userid | 10
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dbid | 63781
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query | UPDATE accounts SET abalance = abalance + $1 WHERE aid = $2;
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calls | 3000
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total_time | 0.645601
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rows | 3000
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</programlisting>
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</sect2>
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<sect2>
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<title>Author</title>
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<para>
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Takahiro Itagaki <email>itagaki.takahiro@oss.ntt.co.jp</email>
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</para>
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</sect2>
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</sect1>
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