From: Tom Lane <tgl@sss.pgh.pa.us>
To: Julien Rouhaud <rjuju123@gmail.com>
cc: Bruce Momjian <bruce@momjian.us>, Magnus Hagander <magnus@hagander.net>,
        Fujii Masao <masao.fujii@oss.nttdata.com>,
        PostgreSQL Developers <pgsql-hackers@lists.postgresql.org>
Subject: Re: compute_query_id and pg_stat_statements
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Comments: In-reply-to Julien Rouhaud <rjuju123@gmail.com>
	message dated "Sun, 25 Apr 2021 16:22:51 +0800"
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Date: Sun, 25 Apr 2021 11:39:55 -0400
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Julien Rouhaud <rjuju123@gmail.com> writes:
> On Sat, Apr 24, 2021 at 01:43:51PM -0400, Tom Lane wrote:
>> I haven't looked, but did we put anything into pg_stat_statements
>> to make it easy to tell if you've messed up this setting?

> You mean apart from from having pg_stat_statements' view/SRFs returning
> nothing?

> I think it's a reasonable use case to sometime disable query_id calculat=
ion,
> eg. if you know that it will only lead to useless bloat in the entry and=
 that
> you won't need the info, so spamming warnings if there are no queryid co=
uld
> cause some pain.

I agree repeated warnings would be bad news.  I was wondering if we could
arrange a single warning at the time pg_stat_statements is preloaded into
the postmaster.  In this way, if you tried to use a configuration file
that used to work, you'd hopefully get some notice about why it no longer
does what you want.  Also, if you are preloading pg_stat_statements, it
seems reasonable to assume that you'd like the global value of the flag
to be "on", even if there are use-cases for transiently disabling it.

I think the way to detect "being loaded into the postmaster" is
	if (IsPostmasterEnvironment && !IsUnderPostmaster)

			regards, tom lane