Re: How can end users know the cause of LR slot sync delays?

On Thu, Aug 28, 2025 at 11:07 AM Ashutosh Sharma <ashu.coek88@gmail.com> wrote:
>
> We have seen cases where slot synchronization gets delayed, for example when the slot is behind the failover standby
orvice versa, and the slot sync worker has to wait for one to catch up with the other. During this waiting period,
usersquerying pg_replication_slots can only see whether the slot has been synchronized or not. If it has already
synchronized,that’s fine, but if synchronization is taking longer, users would naturally want to understand the reason
forthe delay. 
>
> Is there a way for end users to know the cause of slot synchronization delays, so they can take appropriate actions
tospeed it up? 
>
> I understand that server logs are emitted in such cases, but logs are not something end users would want to check
regularly.Moreover, since logging is configuration-based, relevant messages may sometimes be skipped or suppressed. 
>

Currently, the way to see the reason for sync skip is LOGs but I think
it is better to add a new column like sync_skip_reason in
pg_replication_slots. This can show the reasons like
standby_LSN_ahead_remote_LSN. I think ideally users can compare
standby's slot LSN/XMIN with remote_slot being synced. Do you have any
better ideas?

--
With Regards,
Amit Kapila.