Re: pg15b2: large objects lost on upgrade

From: Peter Geoghegan <pg(at)bowt(dot)ie>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: "Jonathan S(dot) Katz" <jkatz(at)postgresql(dot)org>, Noah Misch <noah(at)leadboat(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Andrew Dunstan <andrew(at)dunslane(dot)net>, Bruce Momjian <bruce(at)momjian(dot)us>, Michael Paquier <michael(at)paquier(dot)xyz>, Justin Pryzby <pryzby(at)telsasoft(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>, Shruthi Gowda <gowdashru(at)gmail(dot)com>
Subject: Re: pg15b2: large objects lost on upgrade
Date: 2022-08-03 18:52:18
Message-ID: CAH2-Wz=a7Mw4oKOXATfsK4UQ20H96QxULo0QRRCy0AVWodVYKQ@mail.gmail.com
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On Tue, Aug 2, 2022 at 12:32 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Hmmm ... now that you mention it, I see nothing in 002_pg_upgrade.pl
> that attempts to turn off autovacuum on either the source server or
> the destination. So one plausible theory is that autovac moved the
> numbers since we checked.

It's very easy to believe that my work in commit 0b018fab could make
that happen, which is only a few months old. It's now completely
routine for non-aggressive autovacuums to advance relfrozenxid by at
least a small amount.

For example, when autovacuum runs against either the tellers table or
the branches table during a pgbench run, it will now advance
relfrozenxid, every single time. And to a very recent value. This will
happen in spite of the fact that no freezing ever takes place -- it's
just a consequence of the oldest extant XID consistently being quite
young each time, due to workload characteristics.

--
Peter Geoghegan

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