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From: Nathan Bossart <nathandbossart@gmail.com>
To: Sami Imseih <samimseih@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Andres Freund <andres@anarazel.de>
Cc: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Cc: Rahila Syed <rahilasyed90@gmail.com>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: Improve LWLock tranche name visibility across backends
Date: Mon, 25 Aug 2025 19:14:40 -0500
Message-ID: <aKz8cHo2oBr-6uq5@nathan> (raw)
In-Reply-To: <CAA5RZ0vWh2uxG99iUb3P4nsoDLk0x7Yuai83AbbGs3YZvJM8QQ@mail.gmail.com>
References: <876523.1755635201@sss.pgh.pa.us>
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On Mon, Aug 25, 2025 at 04:59:41PM -0500, Sami Imseih wrote:
> hmm, can we really avoid a shared lock when reading from shared memory?
> considering access for both reads and writes can be concurrent to shared
> memory. We are also taking an exclusive lock when writing a new tranche.

We probably want to hold a lock while we 1) increment LWLockCounter and
copy a new tranche name to memory and 2) while we copy the current value of
LWLockCounter to our backend-local variable.  Otherwise, AFAICT we don't
need one.  We could probably use ShmemLock for this.

-- 
nathan





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