Re: Conflict detection for update_deleted in logical replication

>
> Here is V30 patch set includes the following changes:
>

Thank You for the patch, please find few concerns:

1)
By looking at code of ApplyLauncherMain(), it appears that we stopped
advancing shared-slot's xmin if any of the subscriptions with
retain_conflict_info is disabled. If a subscription is not being used
and is disabled forever (or for quite long), that means xmin will
never be advanced and we will keep accumulating dead-rows even if
other subscribers with retain_conflict_info are actively setting their
oldest_xmin. This could be problematic. Here too, there should be some
way to set stop-conflict-rettention for such a subscription like we do
for 'subscriber not able to catch-up case'.
But I understand it can be complex to implement as we do not know for
how long a subscription is disabled. If we do not find a simpler way
to implement it, then at least we can document such cases and the
risks associated with disabled subscription which has
'retain_conflict_info' enabled. Thoughts?

2)
in wait_for_local_flush(), we have
should_stop_conflict_info_retention() before 'AllTablesyncsReady'
check. Should we give a discount for table-sync time and avoid doing
stop-conflict-retention when table-sync is going on? This is because
table-sync is one time operation (or done only on
subscription-refresh), so we shall not count time spent in table-sync
for 'max_conflict_retention_duration'. We can reset our timer if
table-sync is observed to be going on. Thoughts?

thanks
Shveta