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help / color / mirror / Atom feedFrom: Robert Haas <[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: Tue, 26 Aug 2025 16:21:36 -0400
Message-ID: <CA+TgmoY6_-LcmkSYwKR2F=+vhr_Z3LYxATrnwioWPSNUjSy6=g@mail.gmail.com> (raw)
In-Reply-To: <fvfmkr5kk4nyex56ejgxj3uzi63isfxovp2biecb4bspbjrze7@az2pljabhnff>
References: <fvfmkr5kk4nyex56ejgxj3uzi63isfxovp2biecb4bspbjrze7@az2pljabhnff>
On Fri, Aug 22, 2025 at 3:45 PM Andres Freund <[email protected]> wrote:
> My conclusion from the above is that we ought to:
>
> A) Make Buffer Locks something separate from lwlocks
> B) Merge BufferDesc.state and the content lock
> C) Allow some modifications of BufferDesc.state while holding spinlock
+1 to (A) and (B). No particular opinion on (C) but if it works well, great.
> The order of changes I think makes the most sense is the following:
>
> 1) Allow some modifications while holding the buffer header spinlock
> 2) Reduce buffer pin with just an atomic-sub
> 3) Widen BufferDesc.state to 64 bits
> 4) Implement buffer locking inside BufferDesc.state
> 5) Do IO while holding share-exclusive lock and require all buffer
> modifications to at least hold share exclusive lock
> 6) Wait for AIO when acquiring an exclusive content lock
No strong objections. I certainly like getting to (5) and (6) and I
think those are in the right order. I'm not sure about the rest. I
thought (1) and (2) were the same change after reading your email; and
it surprises me a little bit that (2) is separate from (4). But I'm
sure you have a much better sense of this than I do.
> DOES ANYBODY HAVE A BETTER NAME THAN SHARE-EXCLUSIVE???!?
AFAIK "share exclusive" or "SX" is standard terminology. While I'm not
wholly hostile to the idea of coming up with something else, I don't
think our tendency to invent our own way to do everything is one of
our better tendencies as a project.
--
Robert Haas
EDB: http://www.enterprisedb.com
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Subject: Re: Buffer locking is special (hints, checksums, AIO writes)
In-Reply-To: <CA+TgmoY6_-LcmkSYwKR2F=+vhr_Z3LYxATrnwioWPSNUjSy6=g@mail.gmail.com>
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