Re: Correcting freeze conflict horizon calculation - Mailing list pgsql-hackers

On Tue, Jun 3, 2025 at 1:59 PM Peter Geoghegan <pg@bowt.ie> wrote:
> We do currently end up using OldestXmin-1 as our
> snapshotConflictHorizon when this happens, but as I said in the other
> email, I don't think that that's really required.

Actually, that's not really true, either. That is, it is possible
(though probably very rare) for VACUUM to set an xmax Multi >
OldestMxact with individual members that are still > OldestXmin, while
ultimately being able to set the page all-frozen in the VM.
snapshotConflictHorizon would then come from visibility_cutoff_xid --
which might end up being InvalidTransactionId.


--
Peter Geoghegan