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Re: Exit walsender before confirming remote flush in logical replication

Fujii Masao <masao.fujii@gmail.com>

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From: Fujii Masao <masao.fujii@gmail.com>
To: Chao Li <li.evan.chao@gmail.com>
Cc: Andres Freund <andres@anarazel.de>, Andrey Silitskiy <a.silitskiy@postgrespro.ru>, Alexander Korotkov <aekorotkov@gmail.com>, Greg Sabino Mullane <htamfids@gmail.com>, Japin Li <japinli@hotmail.com>, Ronan Dunklau <ronan@dunklau.fr>, Vitaly Davydov <v.davydov@postgrespro.ru>, "Hayato Kuroda (Fujitsu)" <kuroda.hayato@fujitsu.com>, "Takamichi Osumi (Fujitsu)" <osumi.takamichi@fujitsu.com>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>, "sawada.mshk@gmail.com" <sawada.mshk@gmail.com>, "michael@paquier.xyz" <michael@paquier.xyz>, "peter.eisentraut@enterprisedb.com" <peter.eisentraut@enterprisedb.com>, "dilipbalaut@gmail.com" <dilipbalaut@gmail.com>, "amit.kapila16@gmail.com" <amit.kapila16@gmail.com>, Kyotaro Horiguchi <horikyota.ntt@gmail.com>, Peter Smith <smithpb2250@gmail.com>
Date: 2026-04-24T10:29:08Z
Lists: pgsql-hackers

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On Fri, Apr 24, 2026 at 11:05 AM Chao Li <li.evan.chao@gmail.com> wrote:
> ProcessPendingWrites() calls ProcessRepliesIfAny() in the first place, so if it is possible that, a new COPY message is appended after the already-queued CommandComplete? Which seems to violate the protocol, but I am not sure if that would lead to any trouble.
>
> So, maybe we need a new helper, say ProcessPendingWritesForShutdown(), that loops while pq_is_send_pending(), call WalSndCheckShutdownTimeout() and only wait for WL_SOCKET_WRITEABLE, then pq_flush_if_writable(), on flush failure, maybe WalSndShutdown().

Thanks for the review! You're right.

I added such loop directly in WalSndDone() instead of introducing a new helper
function, since only WalSndDone() needs it and the extra loop does not make
WalSndDone() significantly more complicated.

I've attached an updated patch.

Regards,

-- 
Fujii Masao

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Avoid blocking indefinitely while finishing walsender shutdown

  2. Add wal_sender_shutdown_timeout GUC to limit shutdown wait for replication

  3. pg_upgrade: Add --copy option

  4. Prevent possibility of panics during shutdown checkpoint.

  5. Support clean switchover.