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>Appendix F. Additional Supplied Modules</TD
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><H1
CLASS="SECT1"
><A
NAME="PGSTATSTATEMENTS"
>F.27. pg_stat_statements</A
></H1
><A
NAME="AEN118825"
></A
><P
> The <TT
CLASS="FILENAME"
>pg_stat_statements</TT
> module provides a means for
tracking execution statistics of all SQL statements executed by a server.
</P
><P
> The module must be loaded by adding <TT
CLASS="LITERAL"
>pg_stat_statements</TT
> to
<A
HREF="runtime-config-resource.html#GUC-SHARED-PRELOAD-LIBRARIES"
>shared_preload_libraries</A
> in
<TT
CLASS="FILENAME"
>postgresql.conf</TT
>, because it requires additional shared memory.
This means that a server restart is needed to add or remove the module.
</P
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN118833"
>F.27.1. The <TT
CLASS="STRUCTNAME"
>pg_stat_statements</TT
> view</A
></H2
><P
> The statistics gathered by the module are made available via a system view
named <TT
CLASS="STRUCTNAME"
>pg_stat_statements</TT
>. This view contains one row for
each distinct query text, database ID, and user ID (up to the maximum
number of distinct statements that the module can track). The columns
of the view are shown in <A
HREF="pgstatstatements.html#PGSTATSTATEMENTS-COLUMNS"
>Table F-24</A
>.
</P
><DIV
CLASS="TABLE"
><A
NAME="PGSTATSTATEMENTS-COLUMNS"
></A
><P
><B
>Table F-24. <TT
CLASS="STRUCTNAME"
>pg_stat_statements</TT
> columns</B
></P
><TABLE
BORDER="1"
CLASS="CALSTABLE"
><COL><COL><COL><COL><THEAD
><TR
><TH
>Name</TH
><TH
>Type</TH
><TH
>References</TH
><TH
>Description</TH
></TR
></THEAD
><TBODY
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>userid</TT
></TD
><TD
><TT
CLASS="TYPE"
>oid</TT
></TD
><TD
><TT
CLASS="LITERAL"
><A
HREF="catalog-pg-authid.html"
><TT
CLASS="STRUCTNAME"
>pg_authid</TT
></A
>.oid</TT
></TD
><TD
>OID of user who executed the statement</TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>dbid</TT
></TD
><TD
><TT
CLASS="TYPE"
>oid</TT
></TD
><TD
><TT
CLASS="LITERAL"
><A
HREF="catalog-pg-database.html"
><TT
CLASS="STRUCTNAME"
>pg_database</TT
></A
>.oid</TT
></TD
><TD
>OID of database in which the statement was executed</TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>query</TT
></TD
><TD
><TT
CLASS="TYPE"
>text</TT
></TD
><TD
> </TD
><TD
>Text of the statement (up to <A
HREF="runtime-config-statistics.html#GUC-TRACK-ACTIVITY-QUERY-SIZE"
>track_activity_query_size</A
> bytes)</TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>calls</TT
></TD
><TD
><TT
CLASS="TYPE"
>bigint</TT
></TD
><TD
> </TD
><TD
>Number of times executed</TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>total_time</TT
></TD
><TD
><TT
CLASS="TYPE"
>double precision</TT
></TD
><TD
> </TD
><TD
>Total time spent in the statement, in seconds</TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>rows</TT
></TD
><TD
><TT
CLASS="TYPE"
>bigint</TT
></TD
><TD
> </TD
><TD
>Total number of rows retrieved or affected by the statement</TD
></TR
></TBODY
></TABLE
></DIV
><P
> This view, and the function <CODE
CLASS="FUNCTION"
>pg_stat_statements_reset</CODE
>,
are available only in databases they have been specifically installed into
by running the <TT
CLASS="FILENAME"
>pg_stat_statements.sql</TT
> install script.
However, statistics are tracked across all databases of the server
whenever the <TT
CLASS="FILENAME"
>pg_stat_statements</TT
> module is loaded
into the server, regardless of presence of the view.
</P
><P
> For security reasons, non-superusers are not allowed to see the text of
queries executed by other users. They can see the statistics, however,
if the view has been installed in their database.
</P
><P
> Note that statements are considered the same if they have the same text,
regardless of the values of any out-of-line parameters used in the
statement. Using out-of-line parameters will help to group statements
together and may make the statistics more useful.
</P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN118905"
>F.27.2. Functions</A
></H2
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><CODE
CLASS="FUNCTION"
>pg_stat_statements_reset() returns void</CODE
></DT
><DD
><P
> <CODE
CLASS="FUNCTION"
>pg_stat_statements_reset</CODE
> discards all statistics
gathered so far by <TT
CLASS="FILENAME"
>pg_stat_statements</TT
>.
By default, this function can only be executed by superusers.
</P
></DD
></DL
></DIV
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN118915"
>F.27.3. Configuration parameters</A
></H2
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="VARNAME"
>pg_stat_statements.max</TT
> (<TT
CLASS="TYPE"
>integer</TT
>)</DT
><DD
><P
> <TT
CLASS="VARNAME"
>pg_stat_statements.max</TT
> is the maximum number of
statements tracked by the module (i.e., the maximum number of rows
in the <TT
CLASS="STRUCTNAME"
>pg_stat_statements</TT
> view). If more distinct
statements than that are observed, information about the least-executed
statements is discarded.
The default value is 1000.
This parameter can only be set at server start.
</P
></DD
><DT
><TT
CLASS="VARNAME"
>pg_stat_statements.track</TT
> (<TT
CLASS="TYPE"
>enum</TT
>)</DT
><DD
><P
> <TT
CLASS="VARNAME"
>pg_stat_statements.track</TT
> controls which statements
are counted by the module.
Specify <TT
CLASS="LITERAL"
>top</TT
> to track top-level statements (those issued
directly by clients), <TT
CLASS="LITERAL"
>all</TT
> to also track nested statements
(such as statements invoked within functions), or <TT
CLASS="LITERAL"
>none</TT
> to
disable.
The default value is <TT
CLASS="LITERAL"
>top</TT
>.
Only superusers can change this setting.
</P
></DD
><DT
><TT
CLASS="VARNAME"
>pg_stat_statements.save</TT
> (<TT
CLASS="TYPE"
>boolean</TT
>)</DT
><DD
><P
> <TT
CLASS="VARNAME"
>pg_stat_statements.save</TT
> specifies whether to
save statement statistics across server shutdowns.
If it is <TT
CLASS="LITERAL"
>off</TT
> then statistics are not saved at
shutdown nor reloaded at server start.
The default value is <TT
CLASS="LITERAL"
>on</TT
>.
This parameter can only be set in the <TT
CLASS="FILENAME"
>postgresql.conf</TT
>
file or on the server command line.
</P
></DD
></DL
></DIV
><P
> The module requires additional shared memory amounting to about
<TT
CLASS="VARNAME"
>pg_stat_statements.max</TT
> <TT
CLASS="LITERAL"
>*</TT
>
<A
HREF="runtime-config-statistics.html#GUC-TRACK-ACTIVITY-QUERY-SIZE"
>track_activity_query_size</A
> bytes. Note that this
memory is consumed whenever the module is loaded, even if
<TT
CLASS="VARNAME"
>pg_stat_statements.track</TT
> is set to <TT
CLASS="LITERAL"
>none</TT
>.
</P
><P
> In order to set any of these parameters in your
<TT
CLASS="FILENAME"
>postgresql.conf</TT
> file,
you will need to add <TT
CLASS="LITERAL"
>pg_stat_statements</TT
> to
<A
HREF="runtime-config-custom.html#GUC-CUSTOM-VARIABLE-CLASSES"
>custom_variable_classes</A
>. Typical usage might be:
</P
><PRE
CLASS="PROGRAMLISTING"
># postgresql.conf
shared_preload_libraries = 'pg_stat_statements'
custom_variable_classes = 'pg_stat_statements'
pg_stat_statements.max = 10000
pg_stat_statements.track = all
</PRE
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN118958"
>F.27.4. Sample output</A
></H2
><PRE
CLASS="PROGRAMLISTING"
>$ pgbench -i bench
postgres=# SELECT pg_stat_statements_reset();
$ pgbench -c10 -t300 -M prepared bench
postgres=# \x
postgres=# SELECT * FROM pg_stat_statements ORDER BY total_time DESC LIMIT 3;
-[ RECORD 1 ]------------------------------------------------------------
userid | 10
dbid | 63781
query | UPDATE branches SET bbalance = bbalance + $1 WHERE bid = $2;
calls | 3000
total_time | 20.716706
rows | 3000
-[ RECORD 2 ]------------------------------------------------------------
userid | 10
dbid | 63781
query | UPDATE tellers SET tbalance = tbalance + $1 WHERE tid = $2;
calls | 3000
total_time | 17.1107649999999
rows | 3000
-[ RECORD 3 ]------------------------------------------------------------
userid | 10
dbid | 63781
query | UPDATE accounts SET abalance = abalance + $1 WHERE aid = $2;
calls | 3000
total_time | 0.645601
rows | 3000
</PRE
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN118961"
>F.27.5. Author</A
></H2
><P
> Takahiro Itagaki <CODE
CLASS="EMAIL"
><<A
HREF="mailto:itagaki.takahiro@oss.ntt.co.jp"
>itagaki.takahiro@oss.ntt.co.jp</A
>></CODE
>
</P
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