pg_stat_statementspg_stat_statements
The pg_stat_statements module provides a means for
tracking execution statistics of all SQL statements executed by a server.
The module must be loaded by adding pg_stat_statements> to
in
postgresql.conf>, because it requires additional shared memory.
This means that a server restart is needed to add or remove the module.
The pg_stat_statements view
The statistics gathered by the module are made available via a system view
named pg_stat_statements>. 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 .
pg_stat_statements> columnsNameTypeReferencesDescriptionuseridoidpg_authid.oidOID of user who executed the statementdbidoidpg_database.oidOID of database in which the statement was executedquerytextText of the statement (up to bytes)callsbigintNumber of times executedtotal_timedouble precisionTotal time spent in the statement, in secondsrowsbigintTotal number of rows retrieved or affected by the statement
This view, and the function pg_stat_statements_reset>,
are available only in databases they have been specifically installed into
by running the pg_stat_statements.sql> install script.
However, statistics are tracked across all databases of the server
whenever the pg_stat_statements module is loaded
into the server, regardless of presence of the view.
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.
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.
Functionspg_stat_statements_reset() returns voidpg_stat_statements_reset discards all statistics
gathered so far by pg_stat_statements>.
By default, this function can only be executed by superusers.
Configuration parameterspg_stat_statements.max (integer)
pg_stat_statements.max is the maximum number of
statements tracked by the module (i.e., the maximum number of rows
in the pg_stat_statements> 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.
pg_stat_statements.track (enum)
pg_stat_statements.track controls which statements
are counted by the module.
Specify top> to track top-level statements (those issued
directly by clients), all> to also track nested statements
(such as statements invoked within functions), or none> to
disable.
The default value is top>.
Only superusers can change this setting.
pg_stat_statements.save (boolean)
pg_stat_statements.save specifies whether to
save statement statistics across server shutdowns.
If it is off> then statistics are not saved at
shutdown nor reloaded at server start.
The default value is on>.
This parameter can only be set in the postgresql.conf>
file or on the server command line.
The module requires additional shared memory amounting to about
pg_stat_statements.max*>
bytes. Note that this
memory is consumed whenever the module is loaded, even if
pg_stat_statements.track> is set to none>.
In order to set any of these parameters in your
postgresql.conf> file,
you will need to add pg_stat_statements> to
. Typical usage might be:
# postgresql.conf
shared_preload_libraries = 'pg_stat_statements'
custom_variable_classes = 'pg_stat_statements'
pg_stat_statements.max = 10000
pg_stat_statements.track = all
Sample output
$ 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
Author
Takahiro Itagaki itagaki.takahiro@oss.ntt.co.jp