From 8d459762b10372e48845a49b305f4e1e165fe173 Mon Sep 17 00:00:00 2001
From: Fujii Masao <fujii@postgresql.org>
Date: Fri, 3 Jul 2020 11:35:22 +0900
Subject: [PATCH] Change default of pg_stat_statements.track_planning to off.

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
---
 .../expected/pg_stat_statements.out             |  1 +
 contrib/pg_stat_statements/pg_stat_statements.c |  2 +-
 .../sql/pg_stat_statements.sql                  |  1 +
 doc/src/sgml/pgstatstatements.sgml              | 17 +++++++++++++++--
 4 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/contrib/pg_stat_statements/expected/pg_stat_statements.out b/contrib/pg_stat_statements/expected/pg_stat_statements.out
index f615f8c2bf..c3f013860a 100644
--- a/contrib/pg_stat_statements/expected/pg_stat_statements.out
+++ b/contrib/pg_stat_statements/expected/pg_stat_statements.out
@@ -3,6 +3,7 @@ CREATE EXTENSION pg_stat_statements;
 -- simple and compound statements
 --
 SET pg_stat_statements.track_utility = FALSE;
+SET pg_stat_statements.track_planning = TRUE;
 SELECT pg_stat_statements_reset();
  pg_stat_statements_reset 
 --------------------------
diff --git a/contrib/pg_stat_statements/pg_stat_statements.c b/contrib/pg_stat_statements/pg_stat_statements.c
index cef8bb5a49..65ac301b99 100644
--- a/contrib/pg_stat_statements/pg_stat_statements.c
+++ b/contrib/pg_stat_statements/pg_stat_statements.c
@@ -442,7 +442,7 @@ _PG_init(void)
 							 "Selects whether planning duration is tracked by pg_stat_statements.",
 							 NULL,
 							 &pgss_track_planning,
-							 true,
+							 false,
 							 PGC_SUSET,
 							 0,
 							 NULL,
diff --git a/contrib/pg_stat_statements/sql/pg_stat_statements.sql b/contrib/pg_stat_statements/sql/pg_stat_statements.sql
index 75c10554a8..6ed8e38028 100644
--- a/contrib/pg_stat_statements/sql/pg_stat_statements.sql
+++ b/contrib/pg_stat_statements/sql/pg_stat_statements.sql
@@ -4,6 +4,7 @@ CREATE EXTENSION pg_stat_statements;
 -- simple and compound statements
 --
 SET pg_stat_statements.track_utility = FALSE;
+SET pg_stat_statements.track_planning = TRUE;
 SELECT pg_stat_statements_reset();
 
 SELECT 1 AS "int";
diff --git a/doc/src/sgml/pgstatstatements.sgml b/doc/src/sgml/pgstatstatements.sgml
index a13e28a84c..430d8bf07c 100644
--- a/doc/src/sgml/pgstatstatements.sgml
+++ b/doc/src/sgml/pgstatstatements.sgml
@@ -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>