Re: Exit walsender before confirming remote flush in logical replication

On Wed, Apr 22, 2026 at 3:32 AM Fujii Masao <masao.fujii@gmail.com> wrote:
> Therefore, since replacing pq_flush() with pq_flush_if_writable() seems to
> change behavior only in a limited and acceptable way, I'm thinking to create
> the patch doing that replacement.

On second thought, replacing pq_flush() with pq_flush_if_writable() is not
sufficient. EndCommand(), which WalSndDone() calls before pq_flush(), can also
block when the send buffer is full. That happens because EndCommand() uses
pq_putmessage() rather than pq_putmessage_noblock().

Also, replacing pq_flush() with pq_flush_if_writable() would cause walsender to
give up sending pending messages, including CommandComplete, even before
wal_sender_shutdown_timeout expires. That seems a bit odd. I think it is better
for walsender to continue honoring wal_sender_shutdown_timeout while attempting
to send the final CommandComplete message.

I've attached a patch that addresses both issues. For the first, it introduces
EndCommandExtended(), which allows CommandComplete to be queued with
pq_putmessage_noblock(). For the second, it updates WalSndDone() to use
ProcessPendingWrites() instead of pq_flush(), so the walsender write loop can
continue processing replies and checking replication and shutdown timeouts
while pending output is being flushed.

Thoughts?

Regards,

-- 
Fujii Masao