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pgsql: Use replay LSN as target for cascading logical WAL senders 3+ messages / 1 participants [nested] [flat]
* pgsql: Use replay LSN as target for cascading logical WAL senders @ 2025-06-02 03:04 Michael Paquier <michael@paquier.xyz> 0 siblings, 0 replies; 3+ messages in thread From: Michael Paquier @ 2025-06-02 03:04 UTC (permalink / raw) To: pgsql-committers@lists.postgresql.org Use replay LSN as target for cascading logical WAL senders A cascading WAL sender doing logical decoding (as known as doing its work on a standby) has been using as flush LSN the value returned by GetStandbyFlushRecPtr() (last position safely flushed to disk). This is incorrect as such processes are only able to decode changes up to the LSN that has been replayed by the startup process. This commit changes cascading logical WAL senders to use the replay LSN, as returned by GetXLogReplayRecPtr(). This distinction is important particularly during shutdown, when WAL senders need to send any remaining available data to their clients, switching WAL senders to a caught-up state. Using the latest flush LSN rather than the replay LSN could cause the WAL senders to be stuck in an infinite loop preventing them to shut down, as the startup process does not run when WAL senders attempt to catch up, so they could keep waiting for work that would never happen. Backpatch down to v16, where logical decoding on standbys has been introduced. Author: Alexey Makhmutov <a.makhmutov@postgrespro.ru> Reviewed-by: Ajin Cherian <itsajin@gmail.com> Reviewed-by: Bertrand Drouvot <bertranddrouvot.pg@gmail.com> Reviewed-by: Michael Paquier <michael@paquier.xyz> Discussion: https://postgr.es/m/52138028-7246-421c-9161-4fa108b88070@postgrespro.ru Backpatch-through: 16 Branch ------ REL_16_STABLE Details ------- https://git.postgresql.org/pg/commitdiff/5e6d561bc14db260e7456e02f7a15f46b0302f58 Modified Files -------------- src/backend/replication/walsender.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) ^ permalink raw reply [nested|flat] 3+ messages in thread
* pgsql: Use replay LSN as target for cascading logical WAL senders @ 2025-06-02 03:04 Michael Paquier <michael@paquier.xyz> 0 siblings, 0 replies; 3+ messages in thread From: Michael Paquier @ 2025-06-02 03:04 UTC (permalink / raw) To: pgsql-committers@lists.postgresql.org Use replay LSN as target for cascading logical WAL senders A cascading WAL sender doing logical decoding (as known as doing its work on a standby) has been using as flush LSN the value returned by GetStandbyFlushRecPtr() (last position safely flushed to disk). This is incorrect as such processes are only able to decode changes up to the LSN that has been replayed by the startup process. This commit changes cascading logical WAL senders to use the replay LSN, as returned by GetXLogReplayRecPtr(). This distinction is important particularly during shutdown, when WAL senders need to send any remaining available data to their clients, switching WAL senders to a caught-up state. Using the latest flush LSN rather than the replay LSN could cause the WAL senders to be stuck in an infinite loop preventing them to shut down, as the startup process does not run when WAL senders attempt to catch up, so they could keep waiting for work that would never happen. Backpatch down to v16, where logical decoding on standbys has been introduced. Author: Alexey Makhmutov <a.makhmutov@postgrespro.ru> Reviewed-by: Ajin Cherian <itsajin@gmail.com> Reviewed-by: Bertrand Drouvot <bertranddrouvot.pg@gmail.com> Reviewed-by: Michael Paquier <michael@paquier.xyz> Discussion: https://postgr.es/m/52138028-7246-421c-9161-4fa108b88070@postgrespro.ru Backpatch-through: 16 Branch ------ REL_17_STABLE Details ------- https://git.postgresql.org/pg/commitdiff/87be749c716a5d58ca0a92a56f0c1b7ba8e1fae4 Modified Files -------------- src/backend/replication/walsender.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) ^ permalink raw reply [nested|flat] 3+ messages in thread
* pgsql: Use replay LSN as target for cascading logical WAL senders @ 2025-06-02 03:04 Michael Paquier <michael@paquier.xyz> 0 siblings, 0 replies; 3+ messages in thread From: Michael Paquier @ 2025-06-02 03:04 UTC (permalink / raw) To: pgsql-committers@lists.postgresql.org Use replay LSN as target for cascading logical WAL senders A cascading WAL sender doing logical decoding (as known as doing its work on a standby) has been using as flush LSN the value returned by GetStandbyFlushRecPtr() (last position safely flushed to disk). This is incorrect as such processes are only able to decode changes up to the LSN that has been replayed by the startup process. This commit changes cascading logical WAL senders to use the replay LSN, as returned by GetXLogReplayRecPtr(). This distinction is important particularly during shutdown, when WAL senders need to send any remaining available data to their clients, switching WAL senders to a caught-up state. Using the latest flush LSN rather than the replay LSN could cause the WAL senders to be stuck in an infinite loop preventing them to shut down, as the startup process does not run when WAL senders attempt to catch up, so they could keep waiting for work that would never happen. Backpatch down to v16, where logical decoding on standbys has been introduced. Author: Alexey Makhmutov <a.makhmutov@postgrespro.ru> Reviewed-by: Ajin Cherian <itsajin@gmail.com> Reviewed-by: Bertrand Drouvot <bertranddrouvot.pg@gmail.com> Reviewed-by: Michael Paquier <michael@paquier.xyz> Discussion: https://postgr.es/m/52138028-7246-421c-9161-4fa108b88070@postgrespro.ru Backpatch-through: 16 Branch ------ master Details ------- https://git.postgresql.org/pg/commitdiff/5231ed8262c94936a69bce41f64076630bbd99a2 Modified Files -------------- src/backend/replication/walsender.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) ^ permalink raw reply [nested|flat] 3+ messages in thread
end of thread, other threads:[~2025-06-02 03:04 UTC | newest] Thread overview: 3+ messages (download: mbox mbox.gz follow: Atom feed) -- links below jump to the message on this page -- 2025-06-02 03:04 pgsql: Use replay LSN as target for cascading logical WAL senders Michael Paquier <michael@paquier.xyz> 2025-06-02 03:04 pgsql: Use replay LSN as target for cascading logical WAL senders Michael Paquier <michael@paquier.xyz> 2025-06-02 03:04 pgsql: Use replay LSN as target for cascading logical WAL senders Michael Paquier <michael@paquier.xyz>
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