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From: Melanie Plageman <melanieplageman@gmail.com>
Date: Tue, 2 Sep 2025 17:52:37 -0400
Message-ID: 
 <CAAKRu_a2zU7672weJCGzAE2K44cCwnvsb-BwPh8ET3n1bsKfPQ@mail.gmail.com>
Subject: Re: eliminate xl_heap_visible to reduce WAL (and eventually set VM
 on-access)
To: Kirill Reshke <reshkekirill@gmail.com>
Cc: Andrey Borodin <x4mmm@yandex-team.ru>,
	PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>,
 Andres Freund <andres@anarazel.de>,
	Robert Haas <robertmhaas@gmail.com>, Heikki Linnakangas <hlinnaka@iki.fi>
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On Thu, Aug 28, 2025 at 5:12=E2=80=AFAM Kirill Reshke <reshkekirill@gmail.c=
om> wrote:
>
> I did micro git-blame research here. I spotted only one related change
> [0]. Looks like before this change pin was indeed needed.
> But not after this change, so this visibilitymap_pin is just an oversight=
?
> Related thread is [1]. I quickly checked the discussion in this
> thread, and it looks like no one was bothered about these lines or VM
> logging changes (in this exact pin buffer aspect). The discussion was
> of other aspects of this commit.

Wow, thanks so much for doing that research. Looking at it myself, it
does indeed seem like just an oversight. It isn't harmful since it
won't take another pin, but it is confusing, so I think we should at
least remove it in master. I'm not as sure about back branches.

I would like someone to confirm that there is no way we could end up
with a different block of the VM containing the vm bits for a heap
block during recovery than during normal operation.

- Melanie