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Change default of pg_stat_statements.track_planning to off.

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Since v13 pg_stat_statements is allowed to track the planning time of
statements when track_planning option is enabled. Its default was on.

But this feature could cause more terrible spinlock contentions in
pg_stat_statements. As a result of this, Robins Tharakan reported that
v13 beta1 showed ~45% performance drop at high DB connection counts
(when compared with v12.3) during fully-cached SELECT-only test using
pgbench.

To avoid this performance regression by the default setting,
this commit changes default of pg_stat_statements.track_planning to off.

Back-patch to v13 where pg_stat_statements.track_planning was introduced.

Reported-by: Robins Tharakan
Author: Fujii Masao
Reviewed-by: Julien Rouhaud
Discussion: https://postgr.es/m/2895b53b033c47ccb22972b589050dd9@EX13D05UWC001.ant.amazon.com
This commit is contained in:
Fujii Masao
2020-07-03 11:35:22 +09:00
parent 947456a823
commit d1763ea8c9
4 changed files with 18 additions and 3 deletions
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17
doc/src/sgml/pgstatstatements.sgml
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@ -101,6 +101,8 @@
</para>
<para>
Number of times the statement was planned
(if <varname>pg_stat_statements.track_planning</varname> is enabled,
otherwise zero)
</para></entry>
</row>
@ -110,6 +112,8 @@
</para>
<para>
Total time spent planning the statement, in milliseconds
(if <varname>pg_stat_statements.track_planning</varname> is enabled,
otherwise zero)
</para></entry>
</row>
@ -119,6 +123,8 @@
</para>
<para>
Minimum time spent planning the statement, in milliseconds
(if <varname>pg_stat_statements.track_planning</varname> is enabled,
otherwise zero)
</para></entry>
</row>
@ -128,6 +134,8 @@
</para>
<para>
Maximum time spent planning the statement, in milliseconds
(if <varname>pg_stat_statements.track_planning</varname> is enabled,
otherwise zero)
</para></entry>
</row>
@ -137,6 +145,8 @@
</para>
<para>
Mean time spent planning the statement, in milliseconds
(if <varname>pg_stat_statements.track_planning</varname> is enabled,
otherwise zero)
</para></entry>
</row>
@ -145,7 +155,10 @@
<structfield>stddev_plan_time</structfield> <type>double precision</type>
</para>
<para>
Population standard deviation of time spent planning the statement, in milliseconds
Population standard deviation of time spent planning the statement,
in milliseconds
(if <varname>pg_stat_statements.track_planning</varname> is enabled,
otherwise zero)
</para></entry>
</row>
@ -594,7 +607,7 @@
<para>
<varname>pg_stat_statements.track_planning</varname> controls whether
planning operations and duration are tracked by the module.
The default value is <literal>on</literal>.
The default value is <literal>off</literal>.
Only superusers can change this setting.
</para>
</listitem>