Re: pg15b2: large objects lost on upgrade

On 8/2/22 3:23 PM, Robert Haas wrote:
> On Tue, Aug 2, 2022 at 1:12 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> Not sure what to make of this, except that maybe the test is telling
>> us about an actual bug of exactly the kind it's designed to expose.
>
> That could be, but what would the bug be exactly? It's hard to think
> of a more direct way of setting relminmxid and relfrozenxid than
> updating pg_class. It doesn't seem realistic to suppose that we have a
> bug where setting a column in a system table to an integer value
> sometimes sets it to a slightly larger integer instead. If the values
> on the new cluster seemed like they had never been set, or if it
> seemed like they had been set to completely random values, then I'd
> suspect a bug in the mechanism, but here it seems more believable to
> me to think that we're actually setting the correct values and then
> something - maybe autovacuum - bumps them again before we have a
> chance to look at them.

FWIW (and I have not looked deeply at the code), I was thinking it could
be something along those lines, given 1. the randomness of the
underlying systems of the impacted farm animals and 2. it was only the
three mentioned.

> I'm not quite sure how to rule that theory in or out, though.

Without overcomplicating this, are we able to check to see if autovacuum
ran during the course of the test?

Jonathan