| From: | Melanie Plageman <melanieplageman(at)gmail(dot)com> |
|---|---|
| To: | Alexander Lakhin <exclusion(at)gmail(dot)com> |
| Cc: | Andres Freund <andres(at)anarazel(dot)de>, Tomas Vondra <tomas(at)vondra(dot)me>, David Rowley <dgrowleyml(at)gmail(dot)com>, Kirill Reshke <reshkekirill(at)gmail(dot)com>, Chao Li <li(dot)evan(dot)chao(at)gmail(dot)com>, Andrey Borodin <x4mmm(at)yandex-team(dot)ru>, Xuneng Zhou <xunengzhou(at)gmail(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, Heikki Linnakangas <hlinnaka(at)iki(dot)fi> |
| Subject: | Re: eliminate xl_heap_visible to reduce WAL (and eventually set VM on-access) |
| Date: | 2026-04-20 16:18:24 |
| Message-ID: | CAAKRu_aoK6824z_JtJUWMZk2ST2dXN005Gkt05iitTLD2i4OCw@mail.gmail.com |
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On Sat, Apr 18, 2026 at 2:00 PM Alexander Lakhin <exclusion(at)gmail(dot)com> wrote:
>
> 18.04.2026 19:25, Andres Freund wrote:
>
> >> Could you please look if this can be fixed?
> > When you say fix, I assume you mean address the test instability, rather than
> > actual code changes?
>
> Sure, I didn't mean the new behavior is wrong. Probably changing that
> table to temporary would work
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.
> but I wonder if there are other queries,
> which plans can change due to the same reason.
I think we'll have to take this on a case-by-case basis when we see
failures. While it is certainly possible other tests just rely on
autovacuum not having run and set the page all-visible, many of them
probably have already had to account for that.
- Melanie
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