Re: pg15b2: large objects lost on upgrade

On Tue, Aug 2, 2022 at 3:51 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
> > The test does look helpful and it would catch regressions. Loosely
> > quoting Robert on a different point upthread, we don't want to turn off
> > the alarm just because it's spuriously going off.
> > I think the weakened check is OK (and possibly mimics the real-world
> > where autovacuum runs), unless you see a major drawback to it?
>
> I also think that ">=" is a sufficient requirement.  It'd be a
> bit painful to test if we had to cope with potential XID wraparound,
> but we know that these installations haven't been around nearly
> long enough for that, so a plain ">=" test ought to be good enough.
> (Replacing the simple "eq" code with something that can handle that
> doesn't look like much fun, though.)

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%.

-- 
Robert Haas
EDB: http://www.enterprisedb.com