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Re: Why clearing the VM doesn't require registering vm buffer in wal record

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Andres Freund <andres@anarazel.de>
Cc: Matthias van de Meent <boekewurm+postgres@gmail.com>, Melanie Plageman <melanieplageman@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Heikki Linnakangas <hlinnaka@iki.fi>
Date: 2026-03-05T23:11:43Z
Lists: pgsql-hackers 
On Thu, Mar 5, 2026 at 3:38 PM Andres Freund <andres@anarazel.de> wrote:
> If checksums are enabled, we are already emitting FPIs for the VM when
> *setting* bits in the VM (c.f. log_heap_visible()). I don't see why the story
> for clearing it should be different.  And because there are so few VM pages
> compared to heap pages, I wouldn't expect there to be a meaningful amount of
> VM FPIs outside of very contrived workloads.

Yeah, that's how it seems to me, too, at least as of this moment.

Is there any indication in the code or comments that this was an
intentional omission because somebody thought we could get away
without doing it? Or is just a straight-up goof?

-- 
Robert Haas
EDB: http://www.enterprisedb.com

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Revamp the WAL record format.

  2. Allow I/O reliability checks using 16-bit checksums

  3. Make the visibility map crash-safe.