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From: Melanie Plageman <melanieplageman@gmail.com>
Date: Sat, 28 Feb 2026 13:58:48 -0500
Message-ID: <CAAKRu_a0w7wVZCysJ1s6tEPkdsGyYR4iBSEUefa3Y2nWLx2vSw@mail.gmail.com>
Subject: Re: Unlogged rel fake lsn vs GetVictimBuffer()
To: Andres Freund <andres@anarazel.de>
Cc: pgsql-hackers@postgresql.org, Heikki Linnakangas <hlinnaka@iki.fi>, 
	Peter Geoghegan <pg@bowt.ie>
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On Sat, Feb 28, 2026 at 1:09=E2=80=AFPM Andres Freund <andres@anarazel.de> =
wrote:
>
> I think we ought to fix it, even if it is currently harmless. It seems li=
ke
> it'd not be too hard for this to go wrong in the future, it'd e.g. make s=
ense
> for XLogNeedsFlush() to XLogCtl->LogwrtRqst.Write and wake up walwriter. =
Which
> would have bad consequences if it were done with a fake LSN.
>
> I also think it might be good for XLogNeedsFlush() to have an assertion
> verifying that the LSN in the realm of the possible. It's too easy to fee=
d it
> something entirely bogus right now and never notice.

I agree we should fix it. I noticed it while working on write
combining. I wrote the attached patch to clean up. It's more than you
were mentioning doing, but I think it makes the code nicer. You can of
course also add assertions to XLogNeedsFlush() too.

- Melanie

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