Date: Mon, 26 Apr 2021 13:23:54 -0400
From: Stephen Frost <sfrost@snowman.net>
To: Magnus Hagander <magnus@hagander.net>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Bruce Momjian <bruce@momjian.us>,
	Christoph Berg <myon@debian.org>,
	Peter Eisentraut <peter.eisentraut@enterprisedb.com>,
	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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Greetings,

* Magnus Hagander (magnus@hagander.net) wrote:
> On Mon, Apr 26, 2021 at 6:56 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
> > Stephen Frost <sfrost@snowman.net> writes:
> > > * Bruce Momjian (bruce@momjian.us) wrote:
> > >> Techically, pg_stat_statements can turn on compute_query_id when it =
is
> > >> loaded, even if it is 'off' in postgresql.conf, right?  And
> > >> pg_stat_statements would know if an alternate hash method is being u=
sed,
> > >> right?
> >
> > > +1 on this approach.
> >
> > That'd make it impossible to turn off or adjust afterwards, wouldn't it?
> > I'm afraid the confusion stemming from that would outweigh any simplici=
ty.

I don't know that it actually would, but ...

> That=E4s why I suggested the three value one. Default to a mode where
> it's automatic, which is what the majority is going to want, but have
> a way to explicitly turn it on.

This is certainly fine with me too, though it seems a bit surprising to
me that we couldn't just figure out what the user actually wants based
on what's installed/running for any given combination.

> > In the end, it's not like this is the first time we've ever made an
> > incompatible change in configuration needs; and it won't be the last
> > either.  I don't buy the argument that pg_stat_statements users can't
> > cope with adding the additional setting.  (Of course, we should be
> > careful to call it out as an incompatible change in the release notes.)
>=20
> The fact that we've made changes before that complicated our users
> experience isn't in itself an argument for doing it again though...

I'm generally a proponent of sensible changes across major versions even
if it means that the user has to adjust things, but this seems like a
case where we're punting on something that we really should just be able
to figure out the right answer to and that seems like a step backwards.

Thanks,

Stephen

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