Re: Fsync request queue

From: Andres Freund <andres(at)anarazel(dot)de>
To: Peter Geoghegan <pg(at)bowt(dot)ie>
Cc: Heikki Linnakangas <hlinnaka(at)iki(dot)fi>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Fsync request queue
Date: 2018-04-30 23:08:50
Message-ID: 20180430230850.xo25nx2vkbrzgyxb@alap3.anarazel.de
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On 2018-04-30 16:07:48 -0700, Peter Geoghegan wrote:
> On Mon, Apr 30, 2018 at 4:03 PM, Andres Freund <andres(at)anarazel(dot)de> wrote:
> >> Is this a problem in practice, though? I don't remember seeing any reports
> >> of the fsync queue filling up, after we got the code to compact it. I don't
> >> know if anyone has been looking for that, so that might also explain the
> >> absence of reports, though.
> >
> > It's probably hard to diagnose that as the origin of slow IO from the
> > outside. It's not exactly easy to diagnose that even if you know what's
> > going on.
>
> True, but has anyone ever actually observed a non-zero
> pg_stat_bgwriter.buffers_backend_fsync in the wild after the
> compaction queue stuff was added/backpatched?

Yes.

Greetings,

Andres Freund

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