Attached is some more cleanup on top of patch set v9, removing more dead
stuff related to wraparound. I also removed the oldestOffsetKnown
variable and related code. It was needed to deal with clusters upgraded
from buggy 9.3 and 9.4 era versions, but now that pg_upgrade will
rewrite the SLRUs, it's no longer needed.
Yep, multixact.c looks correct to me. As for "XXX could use SimpleLruTruncate()", yes, for sure.
Actually, xl_multixact_truncate.startTruncMemb is also no longer needed, is it?
Does the pg_upgrade code work though, if you have that buggy situation
where oldestOffsetKnown == false ?
>
> if (!TransactionIdIsValid(*xactptr))
> {
> /* Corner case 3: we must be looking at unused slot zero */
> Assert(offset == 0);
> continue;
> }
After upgrade, this corner case 3 would *not* happen on offset == 0. So
looks like we're still missing test coverage for this upgrade corner case.
Am I understanding correctly that you want to have a test corresponding to the buggy 9.3 and 9.4 era versions?
Do you think we could imitate this scenario on a current master branch like that:
1) generate a couple of offsets segments for the first table;
2) generate more segments for a second table;
3) drop first table;
4) stop pg cluster;
5) remove pg_multixact/offsets/0000
6) upgrade?
PFA, v10-0016-TEST-try-to-replicate-buggy-oldest-offset.patch
This test will fail now, for an obvious reason, but is this case a relevant one?