Feedback-ID: id4a34324:Fastmail
Date: Tue, 2 Dec 2025 20:18:38 -0500
From: Andres Freund <andres@anarazel.de>
To: Peter Geoghegan <pg@bowt.ie>
Cc: Melanie Plageman <melanieplageman@gmail.com>,
	Matthias van de Meent <boekewurm+postgres@gmail.com>,
 pgsql-hackers@postgresql.org,
	Thomas Munro <thomas.munro@gmail.com>, Heikki Linnakangas <hlinnaka@iki.fi>,
	Noah Misch <noah@leadboat.com>, Robert Haas <robertmhaas@gmail.com>,
	Michael Paquier <michael.paquier@gmail.com>
Subject: Re: Buffer locking is special (hints, checksums, AIO writes)
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Hi,

On 2025-12-02 20:12:14 -0500, Peter Geoghegan wrote:
> On Tue, Dec 2, 2025 at 7:47 PM Andres Freund <andres@anarazel.de> wrote:
> > On 2025-11-25 11:54:00 -0500, Andres Freund wrote:
> > > Thanks a lot for that detailed review!  A few questions and comments, before I
> > > try to address the comments in the next version.
> >
> > Here's that new new version, with the following changes
> 
> _bt_check_unique will hold an exclusive buffer lock on the page being
> LP_DEAD-set in the vast majority of cases. Should we expect your
> changes to have no effect at all in that common case?

If we already have an exclusive lock, BufferBeginSetHintBits() will quickly
return true and won't ever return false.


> The BTP_HAS_GARBAGE flag is deprecated these days; we basically don't
> use it anymore. How much value might there be in avoiding setting
> BTP_HAS_GARBAGE as a way of being able to use BufferSetHintBits16 more
> often in nbtree?

None of the MarkBufferDirtyHint() cases in nbtree that had to be modified
looked like they would benefit from BufferSetHintBits16(), since they will
typically modify the page multiple times.  But maybe I'm just misunderstanding
what you mean?

Greetings,

Andres Freund