Re: Performance degradation on concurrent COPY into a single relation in PG16.

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Andres Freund <andres(at)anarazel(dot)de>
Cc: Heikki Linnakangas <hlinnaka(at)iki(dot)fi>, Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>, David Rowley <dgrowleyml(at)gmail(dot)com>, Dean Rasheed <dean(dot)a(dot)rasheed(at)gmail(dot)com>, Jakub Wartak <jakub(dot)wartak(at)enterprisedb(dot)com>, Andrew Dunstan <andrew(at)dunslane(dot)net>, Peter Eisentraut <peter(at)eisentraut(dot)org>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Subject: Re: Performance degradation on concurrent COPY into a single relation in PG16.
Date: 2023-09-06 22:01:53
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Andres Freund <andres(at)anarazel(dot)de> writes:
> On 2023-08-16 13:15:46 +0200, Alvaro Herrera wrote:
>> Since the wins from this patch were replicated and it has been pushed, I
>> understand that this open item can be marked as closed, so I've done
>> that.

> Thanks!

It turns out that this patch is what's making buildfarm member
chipmunk fail in contrib/pg_visibility [1]. That's easily reproduced
by running the test with shared_buffers = 10MB. I didn't dig further
than the "git bisect" result:

$ git bisect bad
82a4edabd272f70d044faec8cf7fd1eab92d9991 is the first bad commit
commit 82a4edabd272f70d044faec8cf7fd1eab92d9991
Author: Andres Freund <andres(at)anarazel(dot)de>
Date: Mon Aug 14 09:54:03 2023 -0700

hio: Take number of prior relation extensions into account

but I imagine the problem is that the patch's more aggressive
relation-extension heuristic is causing the table to have more
pages than the test case expects. Is it really a good idea
for such a heuristic to depend on shared_buffers? If you don't
want to change the heuristic then we'll have to find a way to
tweak this test to avoid it.

regards, tom lane


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