Hi, On Tue, Mar 26, 2024 at 09:30:32AM +0530, shveta malik wrote: > On Mon, Mar 25, 2024 at 12:43 PM shveta malik <shveta.ma...@gmail.com> wrote: > > > > I have one concern, for synced slots on standby, how do we disallow > > invalidation due to inactive-timeout immediately after promotion? > > > > For synced slots, last_inactive_time and inactive_timeout are both > > set. Let's say I bring down primary for promotion of standby and then > > promote standby, there are chances that it may end up invalidating > > synced slots (considering standby is not brought down during promotion > > and thus inactive_timeout may already be past 'last_inactive_time'). > > > > On standby, if we decide to maintain valid last_inactive_time for > synced slots, then invalidation is correctly restricted in > InvalidateSlotForInactiveTimeout() for synced slots using the check: > > if (RecoveryInProgress() && slot->data.synced) > return false;
Right. > But immediately after promotion, we can not rely on the above check > and thus possibility of synced slots invalidation is there. To > maintain consistent behavior regarding the setting of > last_inactive_time for synced slots, similar to user slots, one > potential solution to prevent this invalidation issue is to update the > last_inactive_time of all synced slots within the ShutDownSlotSync() > function during FinishWalRecovery(). This approach ensures that > promotion doesn't immediately invalidate slots, and henceforth, we > possess a correct last_inactive_time as a basis for invalidation going > forward. This will be equivalent to updating last_inactive_time during > restart (but without actual restart during promotion). > The plus point of maintaining last_inactive_time for synced slots > could be, this can provide data to the user on when last time the sync > was attempted on that particular slot by background slot sync worker > or SQl function. Thoughts? Yeah, another plus point is that if the primary is down then one could look at the synced "active_since" on the standby to get an idea of it (depends of the last sync though). The issue that I can see with your proposal is: what if one synced the slots manually (with pg_sync_replication_slots()) but does not use the sync worker? Then I think ShutDownSlotSync() is not going to help in that case. Regards, -- Bertrand Drouvot PostgreSQL Contributors Team RDS Open Source Databases Amazon Web Services: https://aws.amazon.com
