| From: | Peter Geoghegan <pg(at)bowt(dot)ie> |
|---|---|
| To: | Melanie Plageman <melanieplageman(at)gmail(dot)com> |
| Cc: | PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, Andres Freund <andres(at)anarazel(dot)de>, Heikki Linnakangas <hlinnaka(at)iki(dot)fi> |
| Subject: | Re: Correcting freeze conflict horizon calculation |
| Date: | 2025-06-03 18:05:10 |
| Message-ID: | CAH2-WznZx2uYNe8pYKp2BGpiQJzKbVwcSsv6JO+hy53kri8xeA@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Tue, Jun 3, 2025 at 1:59 PM Peter Geoghegan <pg(at)bowt(dot)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
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