Re: Intermittent buildfarm failures on wrasse

From: Andres Freund <andres(at)anarazel(dot)de>
To: pgsql-hackers(at)lists(dot)postgresql(dot)org, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Noah Misch <noah(at)leadboat(dot)com>, Peter Geoghegan <pg(at)bowt(dot)ie>, David Rowley <dgrowleyml(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Subject: Re: Intermittent buildfarm failures on wrasse
Date: 2022-04-15 16:22:41
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On April 15, 2022 11:23:40 AM EDT, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>I wrote:
>> So there's no longer any doubt that something is holding back OldestXmin.
>> I will go put some instrumentation into the code that's computing that.
>The something is the logical replication launcher. In the failing runs,
>it is advertising xmin = 724 (the post-initdb NextXID) and continues to
>do so well past the point where tenk1 gets vacuumed.

That explains it. Before shmstat autovac needed to wait for the stats collector to write out stats. Now it's near instantaneous. So the issue probably existed before, just unlikely to ever be reached.

We can't just ignore database less xmins for non-shared rels, because walsender propagates hot_standby_feedback that way. But we can probably add a flag somewhere indicating whether a database less PGPROC has to be accounted in the horizon for non-shared rels.


Sent from my Android device with K-9 Mail. Please excuse my brevity.

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