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From: Fujii Masao <masao.fujii@gmail.com>
Date: Tue, 24 Mar 2026 15:00:20 +0900
Message-ID: 
 <CAHGQGwFKULfab1NH1+_-+GdpJ8itUaKGU0_4Uwcr-y0MLZchyQ@mail.gmail.com>
Subject: Re: Use SIGTERM instead of SIGUSR1 for slotsync worker to exit during
 promotion?
To: Nisha Moond <nisha.moond412@gmail.com>
Cc: Amit Kapila <amit.kapila16@gmail.com>,
	PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
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On Tue, Mar 24, 2026 at 1:01=E2=80=AFPM Nisha Moond <nisha.moond412@gmail.c=
om> wrote:
> Hi Fujii-san,
>
> I tried reproducing the wait scenario as you mentioned, but could not
> reproduce it.
> Steps I followed:
> 1) Place a debugger in the slotsync worker and hold it at
> fetch_remote_slots() ... -> libpqsrv_get_result()
> 2) Kill the primary.
> 3) Triggered promotion of the standby and release debugger from slotsync =
worker.
>
> The slot sync worker stops when the promotion is triggered and then
> restarts, but fails to connect to the primary. The promotion happens
> immediately.
> ```
> LOG:  received promote request
> LOG:  redo done at 0/0301AD40 system usage: CPU: user: 0.00 s, system:
> 0.02 s, elapsed: 4574.89 s
> LOG:  last completed transaction was at log time 2026-03-23
> 17:13:15.782313+05:30
> LOG:  replication slot synchronization worker will stop because
> promotion is triggered
> LOG:  slot sync worker started
> ERROR:  synchronization worker "slotsync worker" could not connect to
> the primary server: connection to server at "127.0.0.1", port 9933
> failed: Connection refused
> Is the server running on that host and accepting TCP/IP connections?
> ```
>
> I=E2=80=99ll debug this further to understand it better.
> In the meantime, please let me know if I=E2=80=99m missing any step, or i=
f you
> followed a specific setup/script to reproduce this scenario.

Thanks for testing!

If you killed the primary with a signal like SIGTERM, an RST packet might h=
ave
been sent to the slotsync worker at that moment. That allowed the worker to
detect the connection loss and exited the wait state, so promotion could
complete as expected.

To reproduce the issue, you'll need a scenario where the worker cannot dete=
ct
the connection loss. For example, you could block network traffic (e.g., wi=
th
iptables) between the primary and the slotsync worker. The key is to create
a situation where the worker remains stuck waiting for input for a long tim=
e.

Regards,

--=20
Fujii Masao