From: Antonin Houska <ah@cybertec.at>
To: Thomas Munro <thomas.munro@gmail.com>
cc: Tomas Vondra <tomas.vondra@enterprisedb.com>,
    Andres Freund <andres@anarazel.de>,
    PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: walsender "wakeup storm" on PG16,
 likely because of bc971f4025c (Optimize walsender wake up logic using
 condition variables)
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Comments: In-reply-to Thomas Munro <thomas.munro@gmail.com>
   message dated "Tue, 15 Aug 2023 10:55:12 +1200."
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Date: Wed, 16 Aug 2023 13:20:23 +0200
Message-ID: <3029.1692184823@antos>
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Thomas Munro <thomas.munro@gmail.com> wrote:

> On Tue, Aug 15, 2023 at 2:23=E2=80=AFAM Tomas Vondra
> <tomas.vondra@enterprisedb.com> wrote:
> > I'm not familiar with the condition variable code enough to have an
> > opinion, but the patch seems to resolve the issue for me - I can no
> > longer reproduce the high CPU usage.
>=20
> Thanks, pushed.

I try to understand this patch (commit 5ffb7c7750) because I use condition
variable in an extension. One particular problem occured to me, please
consider:

ConditionVariableSleep() gets interrupted, so AbortTransaction() calls
ConditionVariableCancelSleep(), but the signal was sent in between. Shouldn=
't
at least AbortTransaction() and AbortSubTransaction() check the return value
of ConditionVariableCancelSleep(), and re-send the signal if needed?

Note that I'm just thinking about such a problem, did not try to reproduce =
it.

--=20
Antonin Houska
Web: https://www.cybertec-postgresql.com