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From: Nisha Moond <nisha.moond412@gmail.com>
Date: Tue, 31 Mar 2026 11:34:55 +0530
Message-ID: 
 <CABdArM7fPqd9GSXLLyDZfX_bZkAaoJAVDGKSQULfvEvVZZHgsg@mail.gmail.com>
Subject: Re: Use SIGTERM instead of SIGUSR1 for slotsync worker to exit during
 promotion?
To: Fujii Masao <masao.fujii@gmail.com>
Cc: Amit Kapila <amit.kapila16@gmail.com>,
 shveta malik <shveta.malik@gmail.com>,
	PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
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On Mon, Mar 30, 2026 at 4:39=E2=80=AFPM Fujii Masao <masao.fujii@gmail.com>=
 wrote:
>
> On Mon, Mar 30, 2026 at 1:18=E2=80=AFPM Nisha Moond <nisha.moond412@gmail=
.com> wrote:
> > We were using the same log message in two places:
> > check_and_set_sync_info() and HandleSlotSyncMessage().
> > I think =E2=80=9Cwill not start=E2=80=9D fits better in the first case,=
 while =E2=80=9Cwill
> > stop=E2=80=9D makes sense to keep in the second.
>
> Thanks for updating the patch!
>
> With the patch, in my testing, standby promotion always produces
> the following logs:
>
>     LOG:  replication slot synchronization worker will stop because
> promotion is triggered
>     LOG:  replication slot synchronization worker will not start
> because promotion was triggered
>
> It looks like the postmaster immediately restarts the slotsync worker aft=
er
> promotion terminates it, and that new worker then exits on seeing
> SlotSyncCtx->stopSignaled.
>
> IMO, always emitting both messages is a bit confusing. It would be nice t=
o
> suppress the second one if possible.
>
> One idea would be to prevent the restart altogether. For example,
> ProcessSlotSyncMessage() could set SlotSyncCtx->last_start_time to
> a special value (like -1), and SlotSyncWorkerCanRestart() could return
> false (i.e., prevent postmater from starting up slotsync worker) when
> it sees that. Alternatively, SlotSyncWorkerCanRestart() could simply
> check SlotSyncCtx->stopSignaled.
>
> That said, as far as I remember correctly, postmaster is generally not
> supposed to touch shared memory (per the comments in postmaster.c),
> so I'm not sure this approach is acceptable. On the other hand,
> postmaster and the slotsync worker already rely on SlotSyncCtx->last_star=
t_time,
> so perhaps there's some precedent here.
>
IIUC, checking SlotSyncCtx->stopSignaled in SlotSyncWorkerCanRestart()
may not be ideal, as it requires a spinlock to avoid races with the
startup process and it is disallowed to take lock in postmaster main
loop. Whereas, SlotSyncCtx->last_start_time doesn=E2=80=99t need a lock sin=
ce
the postmaster accesses it only when the worker is not alive.

Another option could be to log in check_and_set_sync_info() at DEBUG1
instead of LOG level. This message appears only after stopSignaled is
set, when promotion is already in progress and the first worker has
logged =E2=80=9Cwill stop=E2=80=A6=E2=80=9D. The second worker doesn=E2=80=
=99t do any real work. Since
there=E2=80=99s nothing actionable for users, using DEBUG1 would keep it
useful for debugging (e.g., noticing immediate restarts) while
avoiding extra log noise. Thoughts?

--
Thanks,
Nisha