Re: Feature improvement: can we add queryId for pg_catalog.pg_stat_activity view?

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: Julien Rouhaud <rjuju123(at)gmail(dot)com>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>, Michael Paquier <michael(at)paquier(dot)xyz>, torikoshia <torikoshia(at)oss(dot)nttdata(dot)com>, Atsushi Torikoshi <atorik(at)gmail(dot)com>, Tatsuro Yamada <tatsuro(dot)yamada(dot)tf(at)nttcom(dot)co(dot)jp>, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, Evgeny Efimkin <efimkin(at)yandex-team(dot)ru>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Subject: Re: Feature improvement: can we add queryId for pg_catalog.pg_stat_activity view?
Date: 2021-03-18 13:47:29
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On Thu, Mar 18, 2021 at 07:29:56AM +0800, Julien Rouhaud wrote:
> On Wed, Mar 17, 2021 at 06:32:16PM -0400, Bruce Momjian wrote:
> > OK, is that what everyone wants? I think that is what the patch already
> > does.
> Note exactly. Right now a custom queryid can be computed even if
> compute_queryid is off, if some extension does that in post_parse_analyze_hook.
> I'm assuming that what Robert was thinking was more like:
> if (compute_queryid)
> {
> if (queryid_hook)
> queryId = queryid_hook(...);
> else
> queryId = JumbeQuery(...);
> }
> else
> queryId = 0;
> And that should be done *after* post_parse_analyse_hook so that it's clear that
> this hook is no longer the place to compute queryid.
> Is that what should be done?

No, I don't think so. I think having extensions change behavior
controlled by GUCs is a bad interface.

The docs are going to say that you have to enable compute_queryid to see
the query id in pg_stat_activity and log_line_prefix, but if you install
an extension, the query id will be visible even if you don't have
compute_queryid enabled. I think you need to only honor the hook if
compute_queryid is enabled, and update the pg_stat_statements docs to
say you have to enable compute_queryid for pg_stat_statements to work.

Also, should it be compute_queryid or compute_query_id?

Also, the overhead of computing the query id was reported as 2% --- that
seems quite high for what it does. Do we know why it is so high?

Bruce Momjian <bruce(at)momjian(dot)us>

If only the physical world exists, free will is an illusion.

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