Date: Wed, 14 Oct 2020 10:09:15 -0400
From: Bruce Momjian <bruce@momjian.us>
To: Julien Rouhaud <rjuju123@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Robert Haas <robertmhaas@gmail.com>,
	Michael Paquier <michael@paquier.xyz>,
	Alvaro Herrera <alvherre@alvh.no-ip.org>,
	torikoshia <torikoshia@oss.nttdata.com>,
	Atsushi Torikoshi <atorik@gmail.com>,
	Tatsuro Yamada <tatsuro.yamada.tf@nttcom.co.jp>,
	Tomas Vondra <tomas.vondra@2ndquadrant.com>,
	Evgeny Efimkin <efimkin@yandex-team.ru>,
	PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: Feature improvement: can we add queryId for
 pg_catalog.pg_stat_activity view?
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On Wed, Oct 14, 2020 at 05:43:33PM +0800, Julien Rouhaud wrote:
> On Tue, Oct 13, 2020 at 4:53 AM Bruce Momjian <bruce@momjian.us> wrote:
> >
> > On Mon, Oct 12, 2020 at 04:07:30PM -0400, Tom Lane wrote:
> > > Bruce Momjian <bruce@momjian.us> writes:
> > > > On Mon, Oct 12, 2020 at 02:26:15PM -0400, Tom Lane wrote:
> > > >> Yeah, I agree --- a version number is the wrong way to think about this.
> > >
> > > > The version number was to invalidate _all_ query hashes if the
> > > > algorithm is slightly modified, rather than invalidating just some of
> > > > them, which could lead to confusion.
> > >
> > > Color me skeptical as to the use-case for that.  From users' standpoints,
> > > the hash is mainly going to change when we change the set of parse node
> > > fields that get hashed.  Which is going to happen at every major release
> > > and no (or at least epsilon) minor releases.  So I do not see a point in
> > > tracking an algorithm version number as such.  Seems like make-work.
> >
> > OK, I came up with the hash idea only to address one of your concerns
> > about mismatched hashes for algorithm improvements/changes.  Seems we
> > might as well just document that cross-version hashes are different.
> 
> Ok, so I tried to implement what seems to be the consensus.  First
> attached patch moves the current pgss queryid computation in core,
> with a new compute_queryid GUC (on/off).  One thing I don't really

Why would someone turn compute_queryid off?   Overhead?

-- 
  Bruce Momjian  <bruce@momjian.us>        https://momjian.us
  EnterpriseDB                             https://enterprisedb.com

  The usefulness of a cup is in its emptiness, Bruce Lee