doc: Add note about possible performance overhead by enabling track_planning.

MasaoFujii · MasaoFujii · commit 321fa6a4a26c · 2020-07-06T14:27:09.000+09:00
Enabling pg_stat_statements.track_plaanning may incur a noticeable performance penalty, especially when a fewer kinds of queries are executed on many concurrent connections. This commit documents this note. Back-patch to v13 where pg_stat_statements.track_plaanning was added. Suggested-by: Pavel Stehule Author: Fujii Masao Reviewed-by: Pavel Stehule Discussion: https://postgr.es/m/CAFj8pRC9Jxa8r5i0TNBWLb8mzuaYzEoLq3QOvip0jVpHPOLbVA@mail.gmail.com
diff --git a/doc/src/sgml/pgstatstatements.sgml b/doc/src/sgml/pgstatstatements.sgml
@@ -607,6 +607,9 @@
      <para>
       <varname>pg_stat_statements.track_planning</varname> controls whether
       planning operations and duration are tracked by the module.
+      Enabling this parameter may incur a noticeable performance penalty,
+      especially when a fewer kinds of queries are executed on many
+      concurrent connections.
       The default value is <literal>off</literal>.
       Only superusers can change this setting.
      </para>
