From: Andres Freund <andres@anarazel.de>
To: pgsql-committers@lists.postgresql.org
Subject: pgsql: Base LWLock limits directly on MAX_BACKENDS
Date: Mon, 24 Feb 2025 11:40:39 +0000
Message-ID: <E1tmWpC-000Rm4-2n@gemulon.postgresql.org> (raw)
Base LWLock limits directly on MAX_BACKENDS
Jacob reported that comments for LW_SHARED_MASK referenced a MAX_BACKENDS
limit of 2^23-1, but that MAX_BACKENDS is actually limited to 2^18-1. The
limit was lowered in 48354581a49c, but the comment in lwlock.c wasn't updated.
Instead of just fixing the comment, it seems better to directly base the
lwlock defines on MAX_BACKENDS and add static assertions to ensure that there
is enough space. That way there's no comment that can go out of sync in the
future.
As part of that change I noticed that for some reason the high bit wasn't used
for flags, which seems somewhat odd. Redefine the flag values to start at the
highest bit.
Reported-by: Jacob Brazeal <jacob.brazeal@gmail.com>
Reviewed-by: Jacob Brazeal <jacob.brazeal@gmail.com>
Discussion: https://postgr.es/m/CA+COZaBO_s3LfALq=b+HcBHFSOEGiApVjrRacCe4VP9m7CJsNQ@mail.gmail.com
Branch
------
master
Details
-------
https://git.postgresql.org/pg/commitdiff/cd3ccf88aacb43b7232d6834dc886ff8538c6ce8
Modified Files
--------------
src/backend/storage/lmgr/lwlock.c | 30 ++++++++++++++++++++----------
1 file changed, 20 insertions(+), 10 deletions(-)
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To: pgsql-committers@postgresql.org
Cc: andres@anarazel.de, pgsql-committers@lists.postgresql.org
Subject: Re: pgsql: Base LWLock limits directly on MAX_BACKENDS
In-Reply-To: <E1tmWpC-000Rm4-2n@gemulon.postgresql.org>
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