Re: pg15b2: large objects lost on upgrade

On 8/2/22 4:20 PM, Jonathan S. Katz wrote:
> On 8/2/22 3:51 PM, Tom Lane wrote:
>> "Jonathan S. Katz" <jkatz@postgresql.org> writes:
>>> On 8/2/22 3:39 PM, Tom Lane wrote:
>>>>> I am not in favor of disabling autovacuum in the test: ordinary
>>>>> users are not going to do that while pg_upgrade'ing, so it'd make
>>>>> the test less representative of real-world usage, which seems like
>>>>> a bad idea.  We could either drop this particular check again, or
>>>>> weaken it to allow new relfrozenxid >= old relfrozenxid, likewise
>>>>> relminxid.
>>
>>> 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.)
> 
> ...if these systems are hitting XID wraparound, we have another issue to 
> worry about.
> 
> I started modifying the test to support this behavior, but thought that 
> because 1. we want to ensure the OID is still equal and 2. in the 
> examples you showed, both relfrozenxid or relminxid could increment, we 
> may want to have the individual checks on each column.
> 
> I may be able to conjure something up that does the above, but it's been 
> a minute since I wrote anything in Perl.

Please see attached patch that does the above. Tests pass on my local 
environment (though I did not trigger autovacuum).

Jonathan