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From: Melanie Plageman <melanieplageman@gmail.com>
Date: Tue, 21 Apr 2026 14:41:30 -0400
Message-ID: 
 <CAAKRu_aHBvcHHKmNkAzRdJ_7xc-Q-LhanirqcyVuJEWHbYHbuQ@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 Mon, Apr 20, 2026 at 4:28=E2=80=AFPM Melanie Plageman
<melanieplageman@gmail.com> wrote:
>
> I think we can avoid having relallvisible updated by doing two things:
> 1) moving the analyze test_mode above the create index because the
> create index will scan the table and could set pages all-visible and
> then the analyze may update the statistics
> 2) create the table with autovacuum_enabled =3D false to avoid vacuum
> and analyze running after any of the other table scans may set some
> pages all-visible

So, I don't love that this test relies on pg_class not having been
updated to reflect relallvisible. But, I don't see a good way around
this. If we need the "bad plan" to be a seq scan, then
pg_class.relallvisible can't be updated. As long as only analyze and
vacuum will update pg_class.relallvisible, we can preserve the desired
behavior by disabling autovacuum/analyze for the table and analyzing
it (to get reltuples/relpages) before any scan that could set the VM
for the pages. So, I've done this and committed it in 85ae8ab0533.

- Melanie