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help / color / mirror / Atom feedFrom: Álvaro Herrera <[email protected]>
To: Fujii Masao <[email protected]>
Cc: Bertrand Drouvot <[email protected]>
Cc: Sami Imseih <[email protected]>
Cc: Michael Paquier <[email protected]>
Cc: [email protected]
Cc: Zsolt Parragi <[email protected]>
Subject: Re: Flush some statistics within running transactions
Date: Fri, 30 Jan 2026 10:46:11 +0100
Message-ID: <[email protected]> (raw)
In-Reply-To: <CAHGQGwHttst8tv_WWYNoGGfL1UAq4kiy6dpFXoxEkJwHMS9FtQ@mail.gmail.com>
On 2026-Jan-22, Fujii Masao wrote:
> I haven't read the patch in detail yet, but after applying patch 0001 and
> causing a lock wait (for example, using the steps below), I observed that
> log_lock_waits messages are emitted every second.
Interesting. Bertrand asked me about this. He says[1] he diagnosed this
down to SetLatch being called immediately after the handler runs, and I
wonder if it's correct that other timeout handler functions used for
RegisterTimeout are doing SetLatch(). The SIGALRM handler
handle_sig_alarm() that calls the specific handler function already has
a SetLatch call, so why do we need another one here?
I tested this theory quickly by removing the SetLatch from
IdleStatsUpdateTimeoutHandler() and rerunning the tests. (This one
chosen because it has highest coverage per [2]). Everything passed,
though of course this is probably not proof enough.
Maybe we're just cargo-culting these SetLatch() calls?
[1] https://postgr.es/m/[email protected]
[2] https://coverage.postgresql.org/src/backend/utils/init/postinit.c.gcov.html
--
Álvaro Herrera PostgreSQL Developer — https://www.EnterpriseDB.com/
"Right now the sectors on the hard disk run clockwise, but I heard a rumor that
you can squeeze 0.2% more throughput by running them counterclockwise.
It's worth the effort. Recommended." (Gerry Pourwelle)
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