Re: eliminate xl_heap_visible to reduce WAL (and eventually set VM on-access)

On Thu, Jul 31, 2025 at 6:58 PM Melanie Plageman
<melanieplageman(at)gmail(dot)com> wrote:
>
> The patch "Set-pd_prune_xid-on-insert.txt" can be applied as the last
> patch in the set. It sets pd_prune_xid on insert (so pages filled by
> COPY or insert can also be set all-visible in the VM before they are
> vacuumed). I gave it a .txt extension because it currently fails
> 035_standby_logical_decoding due to a recovery conflict. I need to
> investigate more to see if this is a bug in my patch set or elsewhere
> in Postgres.

I figured out that if we set the VM on-access, we need to enable
hot_standby_feedback in more places in 035_standby_logical_decoding.pl
to avoid recovery conflicts. I've done that in the attached updated
version 6. There are a few other issues in
035_standby_logical_decoding.pl that I reported here [1]. With these
changes, setting pd_prune_xid on insert passes tests. Whether or not
we want to do it (and what the heuristic should be for deciding when
to do it) is another question.

- Melanie

[1] https://www.postgresql.org/message-id/flat/CAAKRu_YO2mEm%3DZWZKPjTMU%3DgW5Y83_KMi_1cr51JwavH0ctd7w%40mail.gmail.com