Re: race condition in pg_class

From: Noah Misch <noah(at)leadboat(dot)com>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Smolkin Grigory <smallkeen(at)gmail(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: race condition in pg_class
Date: 2024-05-13 20:30:38
Message-ID: 20240513203038.d7.nmisch@google.com
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On Mon, May 13, 2024 at 03:53:08PM -0400, Robert Haas wrote:
> On Sun, May 12, 2024 at 7:29 PM Noah Misch <noah(at)leadboat(dot)com> wrote:
> > - [consequences limited to transient failure] Since a PROC_IN_VACUUM backend's
> > xmin does not stop pruning, an MVCC scan in that backend can find zero
> > tuples when one is live. This is like what all backends got in the days of
> > SnapshotNow catalog scans. See the pgbench test suite addition. (Perhaps
> > the fix is to make VACUUM do its MVCC scans outside of PROC_IN_VACUUM,
> > setting that flag later and unsetting it earlier.)
>
> Are you saying that this is a problem already, or that the patch
> causes it to start happening? If it's the former, that's horrible.

The former.

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