On Tue, Jul 9, 2024 at 12:42 AM John H <johnh...@gmail.com> wrote: > > > > Can we make it a default > > behavior that logical slots marked with a failover option will wait > > for 'synchronous_standby_names' as per your patch's idea unless > > 'standby_slot_names' is specified? I don't know if there is any value > > in setting the 'failover' option for a slot without specifying > > 'standby_slot_names', so was wondering if we can additionally tie it > > to 'synchronous_standby_names'. Any better ideas? > > > > No, I think that works pretty cleanly actually. Reserving some special > keyword isn't great > which is the only other thing I can think of. I've updated the patch > and tests to reflect that. > > Attached the patch that addresses these changes.
Thank You for the patch. I like the overall idea, it is a useful one and will make user experience better. Please find few comments. 1) I agree with the idea that instead of introducing new GUC, we can make failover logical slots wait on 'synchronous_standby_names', but this will leave user no option to unlink failover-enabled logical subscribers from the wait on synchronous standbys. We provide user a way to switch off automatic slot-sync by disabling 'sync_replication_slots' and we also provide user a way to manually sync the slots using function 'pg_sync_replication_slots()' and nowhere we make it mandatory to set 'synchronized_standby_slots'; in fact in docs, it is a recommended setting and not a mandatory one. User can always create failover slots, switch off automatic slot sync and disable wait on standbys by not specifying 'synchronized_standby_slots' and do the slot-sync and consistency checks manually when needed. I feel, for worst case scenarios, we should provide user an option to delink failover-enabled logical subscriptions from 'synchronous_standby_names'. We can have 'synchronized_standby_slots' (standby_slot_names) to accept one such option as in 'SAME_AS_SYNCREP_STANDBYS' or say 'DEFAULT'. So when 'synchronous_standby_names' is comma separated list, we pick those slots; if it is empty, then no wait on standbys, and if its value is 'DEFAULT' as configured by user, then go with 'synchronous_standby_names'. Thoughts? 2) When 'synchronized_standby_slots' is configured but standby named in it is down blocking logical replication, then we get a WARNING in subscriber's log file: WARNING: replication slot "standby_2" specified in parameter synchronized_standby_slots does not have active_pid. DETAIL: Logical replication is waiting on the standby associated with "standby_2". HINT: Consider starting standby associated with "standby_2" or amend parameter synchronized_standby_slots. But OTOH, when 'synchronous_standby_names' is configured instead of 'synchronized_standby_slots' and any of the standbys listed is down blocking logical replication, we do not get any sort of warning. It is inconsistent behavior. Also user might be left clueless on why subscribers are not getting changes. thanks Shveta
