Re: pg15b2: large objects lost on upgrade

On Wed, Aug 3, 2022 at 1:20 PM Andres Freund <andres@anarazel.de> wrote:
> > I don't really like this approach. Imagine that the code got broken in
> > such a way that relfrozenxid and relminmxid were set to a value chosen
> > at random - say, the contents of 4 bytes of unallocated memory that
> > contained random garbage. Well, right now, the chances that this would
> > cause a test failure are nearly 100%. With this change, they'd be
> > nearly 0%.
>
> Can't that pretty easily be addressed by subsequently querying txid_current(),
> and checking that the value isn't newer than that?

It couldn't hurt to do that as well, in passing (at the same time as
testing that newrelfrozenxid >= oldrelfrozenxid directly). But
deliberately running VACUUM afterwards seems like a good idea. We
really ought to expect VACUUM to catch cases where
relfrozenxid/relminmxid is faulty, at least in cases where it can be
proven wrong by noticing some kind of inconsistency.

-- 
Peter Geoghegan