Date: Wed, 14 Oct 2020 10:25:23 -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?
Message-ID: <20201014142523.GA9415@momjian.us>
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On Wed, Oct 14, 2020 at 10:21:24PM +0800, Julien Rouhaud wrote:
> On Wed, Oct 14, 2020 at 10:09 PM Bruce Momjian <bruce@momjian.us> wrote:
> > > > 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?
> 
> Yes, or possibly to use a different algorithm.

Is there a measureable overhead when this is turned on, since it is off
by default and maybe should default to on.

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

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