Re: track_planning causing performance regression

On Wed, Apr 21, 2021 at 10:40:07AM -0500, Justin Pryzby wrote:
> On Thu, Apr 22, 2021 at 12:13:17AM +0900, Fujii Masao wrote:
> > On 2021/04/21 23:53, Justin Pryzby wrote:
> > > Or:
> > >
> > > Enabling this parameter may incur a noticeable performance penalty,
> > > especially similar queries are executed by many concurrent connections
> > > and compete to update a small number of pg_stat_statements entries.
> >
> > I prefer this. But what about using "identical" instead of "similar"
> > because pg_stat_statements docs already uses "identical" in some places?
>
> I also missed "when", again...
>
> > > Enabling this parameter may incur a noticeable performance penalty,
> > > especially when queries with identical structure are executed by many concurrent connections
> > > which compete to update a small number of pg_stat_statements entries.

Checking back - here's the latest patch.

diff --git a/doc/src/sgml/pgstatstatements.sgml b/doc/src/sgml/pgstatstatements.sgml
index 930081c429..9e98472c5c 100644
--- a/doc/src/sgml/pgstatstatements.sgml
+++ b/doc/src/sgml/pgstatstatements.sgml
@@ -696,8 +696,9 @@
<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 queries with the same queryid are executed on many
- concurrent connections.
+ especially when queries with identical structure are executed by many
+ concurrent connections which compete to update a small number of
+ pg_stat_statements entries.
The default value is <literal>off</literal>.
Only superusers can change this setting.
</para>