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

On Tue, Apr 21, 2026 at 5:37 PM Melanie Plageman
<melanieplageman(at)gmail(dot)com> wrote:
>
> On Mon, Apr 20, 2026 at 12:18 PM Melanie Plageman
> <melanieplageman(at)gmail(dot)com> wrote:
> >
> >
> > Yes, I think changing it to a temp table is the easiest fix. We could
> > also do autovacuum_enabled=false, I think, but making it a temp table
> > seems cleanest.
> >
> > I wonder if we should move the EXPLAIN test above the results queries,
> > then throw in a vacuum in between some of them so we exercise btree
> > gist as a bitmap heap scan and as an index only scan. It could provide
> > a little bit more coverage? Or maybe that isn't actually extra
> > coverage. I'm not sure.
>
> I kept it simple and just committed making it a temp table in 62407d26b7c

An adversarial LLM review of this patch series found that I call
visibilitymap_pin() after taking a cleanup lock on the heap page in
the on-access pruning path -- which is not good. Here is a small patch
to fix that. Doing it before we're sure we can get the cleanup lock
could occasionally lead to an unneeded pin, but such situations should
be uncommon.

- Melanie