Re: Correcting freeze conflict horizon calculation

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: 2026-03-10 16:53:42
Message-ID: CAH2-WzkrqYvLGVo8pkjZjdcv9PitWNYXr1b1RALtDv=f=womiw@mail.gmail.com
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On Tue, Mar 10, 2026 at 12:12 PM Melanie Plageman
<melanieplageman(at)gmail(dot)com> wrote:
> I've taken a stab at distilling down the comment and put it above
> heap_prepare_freeze_tuple(). This is what I came up with:
>
> * FreezePageConflictXid is advanced only for xmin/xvac freezing, not for xmax
> * changes. We only remove xmax state here when it is lock-only, or when the
> * updater XID (including an updater member of a MultiXact) must be aborted;
> * otherwise, the tuple would already be removable. Neither case affects
> * visibility on a standby.
>
> I don't mention why we need a conflict horizon when freezing there,
> but I do in the comment above the struct member:

> Do these seem correct enough and understandable?

Yes. This LGTM.

--
Peter Geoghegan

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