From: Bruce Momjian <bruce@momjian.us>
To: Julien Rouhaud <rjuju123@gmail.com>
Cc: Alvaro Herrera <alvherre@alvh.no-ip.org>
Cc: Hannu Krosing <hannuk@google.com>
Cc: Robert Haas <robertmhaas@gmail.com>
Cc: Pavel Stehule <pavel.stehule@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Michael Paquier <michael@paquier.xyz>
Cc: torikoshia <torikoshia@oss.nttdata.com>
Cc: Atsushi Torikoshi <atorik@gmail.com>
Cc: Tatsuro Yamada <tatsuro.yamada.tf@nttcom.co.jp>
Cc: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Cc: Evgeny Efimkin <efimkin@yandex-team.ru>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: Feature improvement: can we add queryId for pg_catalog.pg_stat_activity view?
Date: Thu, 1 Apr 2021 15:27:11 -0400
Message-ID: <20210401192711.GD18031@momjian.us> (raw)
In-Reply-To: <20210401182802.d7o632hxdgwita32@nol>
References: <20210331130643.GA11608@momjian.us>
<20210331141845.GA958@alvherre.pgsql>
<20210401150524.ylqpsskvmnwsf6eg@nol>
<20210401153015.kfyoxszzxtqum7os@nol>
<20210401175642.GA18031@momjian.us>
<20210401175915.GB18031@momjian.us>
<20210401182802.d7o632hxdgwita32@nol>
On Fri, Apr 2, 2021 at 02:28:02AM +0800, Julien Rouhaud wrote:
> Unless I'm missing something query_string isn't a global variable, it's a
> parameter passed to exec_simple_query() from postgresMain().
>
> It's then passed to the stats collector to be able to be displayed in
> pg_stat_activity through pgstat_report_activity() a bit like what I do for the
> queryid.
>
> There's a global variable debug_query_string, but it's only for debugging
> purpose.
>
> > > I wonder if the query hash
> > > should be a global variable too --- this would more clearly match how we
> > > handle top-level info like query_string. Digging into the stats system
> > > to get top-level info does seem odd.
>
> The main difference is that there's a single top level query_string,
> even if it contains multiple statements. But there would be multiple queryid
> calculated in that case and we don't want to change it during a top level
> multi-statements execution, so we can't use the same approach.
>
> Also, the query_string is directly logged from this code path, while the
> queryid is logged as a log_line_prefix, and almost all the code there also
> retrieve information from some shared structure.
>
> And since it also has to be available in pg_stat_activity, having a single
> source of truth looked like a better approach.
>
> > Also, if you go in that direction, make sure the hash it set in the same
> > places the query string is set, though I am unclear how extensions would
> > handle that.
>
> It should be transparent for application, it's extracting the first queryid
> seen for each top level statement and export it. The rest of the code still
> continue to see the queryid that corresponds to the really executed single
> statement.
OK, I am happy with your design decisions, thanks.
--
Bruce Momjian <bruce@momjian.us> https://momjian.us
EDB https://enterprisedb.com
If only the physical world exists, free will is an illusion.
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To: pgsql-hackers@postgresql.org
Cc: bruce@momjian.us, rjuju123@gmail.com, alvherre@alvh.no-ip.org, hannuk@google.com, robertmhaas@gmail.com, pavel.stehule@gmail.com, tgl@sss.pgh.pa.us, michael@paquier.xyz, torikoshia@oss.nttdata.com, atorik@gmail.com, tatsuro.yamada.tf@nttcom.co.jp, tomas.vondra@2ndquadrant.com, efimkin@yandex-team.ru, pgsql-hackers@lists.postgresql.org
Subject: Re: Feature improvement: can we add queryId for pg_catalog.pg_stat_activity view?
In-Reply-To: <20210401192711.GD18031@momjian.us>
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