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In-Reply-To: <e71cf1ab-92cc-479a-b1e9-39f663867b90@gmail.com>
From: Melanie Plageman <melanieplageman@gmail.com>
Date: Mon, 20 Apr 2026 12:18:24 -0400
Message-ID: 
 <CAAKRu_aoK6824z_JtJUWMZk2ST2dXN005Gkt05iitTLD2i4OCw@mail.gmail.com>
Subject: Re: eliminate xl_heap_visible to reduce WAL (and eventually set VM
 on-access)
To: Alexander Lakhin <exclusion@gmail.com>
Cc: Andres Freund <andres@anarazel.de>, Tomas Vondra <tomas@vondra.me>,
	David Rowley <dgrowleyml@gmail.com>, Kirill Reshke <reshkekirill@gmail.com>,
	Chao Li <li.evan.chao@gmail.com>, Andrey Borodin <x4mmm@yandex-team.ru>,
	Xuneng Zhou <xunengzhou@gmail.com>, Robert Haas <robertmhaas@gmail.com>,
	PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>,
 Heikki Linnakangas <hlinnaka@iki.fi>
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On Sat, Apr 18, 2026 at 2:00=E2=80=AFPM Alexander Lakhin <exclusion@gmail.c=
om> 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, rathe=
r 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=3Dfalse, 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