Re: [patch] BUG #15005: ANALYZE can make pg_class.reltuples inaccurate.

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: David Gould <daveg(at)sonic(dot)net>
Cc: Jeff Janes <jeff(dot)janes(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, Alina Alexeeva <alexeeva(at)adobe(dot)com>, Ullas Lakkur Raghavendra <lakkurra(at)adobe(dot)com>
Subject: Re: [patch] BUG #15005: ANALYZE can make pg_class.reltuples inaccurate.
Date: 2018-03-12 14:43:36
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David Gould <daveg(at)sonic(dot)net> writes:
> On Wed, 7 Mar 2018 21:39:08 -0800
> Jeff Janes <jeff(dot)janes(at)gmail(dot)com> wrote:
>> As for preventing it in the first place, based on your description of your
>> hardware and operations, I was going to say you need to increase the max
>> number of autovac workers, but then I remembered you from "Autovacuum slows
>> down with large numbers of tables. More workers makes it slower" (
>> So you are probably still suffering from that? Your patch from then seemed
>> to be pretty invasive and so controversial.

> We have been building from source using that patch for the worker contention
> since then. It's very effective, there is no way we could have continued to
> rely on autovacuum without it. It's sort of a nuisance to keep updating it
> for each point release that touches autovacuum, but here we are.

Re-reading that thread, it seems like we should have applied Jeff's
initial trivial patch[1] (to not hold AutovacuumScheduleLock across
table_recheck_autovac) rather than waiting around for a super duper
improvement to get agreed on. I'm a bit tempted to go do that;
if nothing else, it seems simple enough to back-patch, unlike most
of the rest of what was discussed.

regards, tom lane


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