Re: [HACKERS] Re: pgsql: Avoid extra locks in GetSnapshotData if old_snapshot_threshold <

From: Andres Freund <andres(at)anarazel(dot)de>
To: Kevin Grittner <kgrittn(at)gmail(dot)com>
Cc: Ants Aasma <ants(dot)aasma(at)eesti(dot)ee>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Noah Misch <noah(at)leadboat(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Kevin Grittner <kgrittn(at)postgresql(dot)org>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>, "pgsql-committers(at)postgresql(dot)org" <pgsql-committers(at)postgresql(dot)org>
Subject: Re: [HACKERS] Re: pgsql: Avoid extra locks in GetSnapshotData if old_snapshot_threshold <
Date: 2016-05-07 22:11:05
Message-ID: 20160507221105.rjjtdir65obkjn2g@alap3.anarazel.de
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On 2016-05-06 20:28:27 -0500, Kevin Grittner wrote:
> On Fri, May 6, 2016 at 7:48 PM, Andres Freund <andres(at)anarazel(dot)de> wrote:
> > On 2016-05-06 19:43:24 -0500, Kevin Grittner wrote:
> >> It's disappointing that I am not getting more consistent numbers,
> >> but NUMA can be hard to manage that way.
> >
> > FWIW, in my experience, unless you disable autovacuum (or rather
> > auto-analyze), the effects from non-predicable analyze runs with
> > long-running snapshots are worse. I mean the numa effects suck, but in
> > r/w workload effects of analyze are often much worse.
>
> Hm. But the benefits of the patch are not there if autovacuum is
> off. I'm gonna need to ponder the best way to test given all that.

It's sufficient to set the threshhold for analyze very high, as vacuum
itself doesn't have that problem. I basically just set
autovacuum_analyze_threshold to INT_MAX , that alleviates the problem
for normal runs.

Andres

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