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From: Mihail Nikalayeu <mihailnikalayeu@gmail.com>
Date: Sat, 23 Aug 2025 12:31:53 +0200
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 <CADzfLwV65qEO1z02Spse47pNP-vGLhaBZpDXfftb2w-28UMf5A@mail.gmail.com>
Subject: Re: Buffer locking is special (hints, checksums, AIO writes)
To: Andres Freund <andres@anarazel.de>
Cc: pgsql-hackers@postgresql.org,
 Melanie Plageman <melanieplageman@gmail.com>,
	Thomas Munro <thomas.munro@gmail.com>, Heikki Linnakangas <hlinnaka@iki.fi>,
 Noah Misch <noah@leadboat.com>
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Hello, Andres!

Andres Freund <andres@anarazel.de>:
>
>    As part of that introduce a new lock level in-between share and exclusive
>    locks (provisionally called share-exclusive, but I hate it). The new lock
>    level allows other share lockers, but can only be held by one backend.
>
>    This allows to change the rules so that:
>
>    1) Share lockers are not allowed to modify buffers anymore
>    2) Hint bits need the new lock mode (conditionally upgrading the lock in SetHintBits())
>    3) Write IO needs to the new lock level

IIUC, it may be mapped to existing locking system:

BUFFER_LOCK_SHARE          ---->      AccessShareLock
new lock mode                           ---->     ExclusiveLock
BUFFER_LOCK_EXCLUSIVE   ---->     AccessExclusiveLock

So, it all may be named:

BUFFER_LOCK_ACCESS_SHARE
BUFFER_LOCK_EXCLUSIVE
BUFFER_LOCK_ACCESS_EXCLUSIVE

being more consistent with table-level locking system.

Greetings,
Mikhail.