Re: Flush some statistics within running transactions

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/aXJUK90lKXw3wrZn@ip-10-97-1-34.eu-west-3.compute.internal
[2] https://coverage.postgresql.org/src/backend/utils/init/postinit.c.gcov.html

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Álvaro Herrera PostgreSQL Developer — https://www.EnterpriseDB.com/
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