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From: Mihail Nikalayeu <[email protected]>
To: Andres Freund <[email protected]>
Cc: [email protected]
Cc: Melanie Plageman <[email protected]>
Cc: Thomas Munro <[email protected]>
Cc: Heikki Linnakangas <[email protected]>
Cc: Noah Misch <[email protected]>
Subject: Re: Buffer locking is special (hints, checksums, AIO writes)
Date: Sat, 23 Aug 2025 12:31:53 +0200
Message-ID: <CADzfLwV65qEO1z02Spse47pNP-vGLhaBZpDXfftb2w-28UMf5A@mail.gmail.com> (raw)
In-Reply-To: <fvfmkr5kk4nyex56ejgxj3uzi63isfxovp2biecb4bspbjrze7@az2pljabhnff>
References: <fvfmkr5kk4nyex56ejgxj3uzi63isfxovp2biecb4bspbjrze7@az2pljabhnff>

Hello, Andres!

Andres Freund <[email protected]>:
>
>    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.

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