Re: Understanding when VM record needs snapshot conflict horizon

On Sun, May 25, 2025 at 6:45 AM Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
>
> IMHO, if we include snapshot conflict horizon in cases where it is not
> necessary, don't you think it will impact performance on standby?
> because now it has to loop through the procarray on standby to check
> whether there is any conflict before applying this WAL.

Yep, that's a good point. In my patch set to combine the prune/freeze
record and visible record, the only time we could omit the snapshot
conflict horizon after phase I of vacuum in this combined record is
when the heap page was unmodified by phase I and the heap page was
already marked all-visible in the VM and is only being set all-frozen.
I will make sure that the snapshot conflict horizon is omitted in that
case to ensure we don't spend more time on the standby to check for
conflicts.

- Melanie