Re: compute_query_id and pg_stat_statements

From: Stephen Frost <sfrost(at)snowman(dot)net>
To: Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Magnus Hagander <magnus(at)hagander(dot)net>, Bruce Momjian <bruce(at)momjian(dot)us>, Christoph Berg <myon(at)debian(dot)org>, Peter Eisentraut <peter(dot)eisentraut(at)enterprisedb(dot)com>, Fujii Masao <masao(dot)fujii(at)oss(dot)nttdata(dot)com>, PostgreSQL Developers <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Subject: Re: compute_query_id and pg_stat_statements
Date: 2021-04-26 17:45:49
Message-ID: 20210426174549.GZ20766@tamriel.snowman.net
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Greetings,

* Alvaro Herrera (alvherre(at)alvh(dot)no-ip(dot)org) wrote:
> On 2021-Apr-26, Tom Lane wrote:
>
> > Stephen Frost <sfrost(at)snowman(dot)net> writes:
> > > * Magnus Hagander (magnus(at)hagander(dot)net) wrote:
> > >> Thatäs 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.
> >
> > I'd be on board with having pg_stat_statement's pg_init function do
> > something to adjust the setting, if we can figure out how to do that
> > in a way that's not confusing in itself. I'm not sure though that
> > the GUC engine offers a good way.
>
> I think it's straightforward, if we decouple the tri-valued enum used
> for guc.c purposes from a separate boolean that actually enables the
> feature. GUC sets the boolean to "off" initially when it sees the enum
> as "auto", and then pg_stat_statement's _PG_init modifies it during its
> own startup as needed.
>
> So the user can turn the GUC off, and then pg_stat_statement does
> nothing and there is no performance drawback; or leave it "auto" and
> it'll only compute query_id if pg_stat_statement is loaded; or leave it
> on if they want the query_id for other purposes.

Yeah, this is more-or-less the same as what I was just proposing in an
email that crossed this one. Using a separate boolean would certainly
be fine.

Thanks,

Stephen

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