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

From: Andres Freund <andres(at)anarazel(dot)de>
To: Melanie Plageman <melanieplageman(at)gmail(dot)com>
Cc: PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, Robert Haas <robertmhaas(at)gmail(dot)com>, Heikki Linnakangas <hlinnaka(at)iki(dot)fi>, Noah Misch <noah(at)leadboat(dot)com>
Subject: Re: Why clearing the VM doesn't require registering vm buffer in wal record
Date: 2026-03-05 20:16:28
Message-ID: 7wh5hrgp434pxcgdfsokfy4m2dib4v3weulxmymtihtr4zxhxh@zaizt4hyh3q3
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Hi,

On 2026-03-05 14:56:13 -0500, Melanie Plageman wrote:
> Today Andres and I noticed that heap_{update,insert,delete}() don't
> register the VM buffer when they are clearing the VM. I was under the
> impression that any buffers modified needed to be registered in the
> WAL record. Without which, you'll never do an FPI. It seems like this
> could cause checksum failures. What are we missing?

Besides checksum errors, I was also worried that this would break
pg_rewind. But it seems we're saved by pg_rewind only parsing the WAL for
changes to the main fork.

But it does seem like it could be a problem for incremental backup /
walsummarizer?

Greetings,

Andres Freund

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