Date: Mon, 13 May 2024 13:30:38 -0700
From: Noah Misch <noah@leadboat.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Smolkin Grigory <smallkeen@gmail.com>,
	pgsql-hackers@postgresql.org
Subject: Re: race condition in pg_class
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@leadboat.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.