Re: Conflict detection for update_deleted in logical replication

On Wed, Aug 13, 2025 at 4:15 PM shveta malik <shveta(dot)malik(at)gmail(dot)com> wrote:
>
> On Wed, Aug 13, 2025 at 10:41 AM Zhijie Hou (Fujitsu)
> <houzj(dot)fnst(at)fujitsu(dot)com> wrote:
> >
> >
> > Here is the V61 patch set which addressed above comments and the comment by Nisha[2].
> >
>
> Thank You for the patch. I tested the patch, please find a few comments:
>
> 1)
> Now when it stops-retention and later resumes it due to the fact that
> max_duration is meanwhile altered to 0, I get log:
>
> LOG: logical replication worker for subscription "sub1" resumes
> retaining the information for detecting conflicts
> DETAIL: The time spent applying changes up to LSN 0/17DD728 is now
> within the maximum limit of 0 ms.
>
> I did not get which lsn it is pointing to? Is it some dangling lsn
> from when it was retaining info? Also the msg looks odd, when it says
> 'is now within the maximum limit of 0 ms.'
>
> 2)
> While stopping the message is:
> LOG: logical replication worker for subscription "sub1" will stop
> retaining conflict information
> DETAIL: The time spent advancing the non-removable transaction ID has
> exceeded the maximum limit of 1000 ms.
>
> And while resuming:
> logical replication worker for subscription "sub1" resumes retaining
> the information for detecting conflicts
> ----------
>
> We can make both similar. Both can have 'retaining the information for
> detecting conflicts' instead of 'conflict information' in first one.
>
> 3)
> I believe the tenses should also be updated. When stopping, we can say:
>
> Logical replication worker for subscription "sub1" has stopped...
>
> This is appropriate because it has already stopped by pre-setting
> oldest_nonremovable_xid to Invalid.
>
> When resuming, we can say:
> Logical replication worker for subscription "sub1" will resume...
>
> This is because it will begin resuming from the next cycle onward,
> specifically after the launcher sets its oldest_xid.
>
> 4)
> For the DETAIL part of resume and stop messages, how about these:
>
> The retention duration for information used in conflict detection has
> exceeded the limit of xx.
> The retention duration for information used in conflict detection is
> now within the acceptable limit of xx.
> The retention duration for information used in conflict detection is
> now indefinite.
>

5)
Say there 2-3 subs, all have stopped-retention and the slot is set to
have invalid xmin; now if I create a new sub, it will start with
stopped-flag set to true due to the fact that slot has invalid xmin to
begin with. But then immediately, it will dump a resume message. It
looks odd, as at first, it has not even stopped, as it is a new sub.
Is there anything we can do to improve this situation?

Logs:
2025-08-13 15:13:01.197 IST [61926] LOG: logical replication apply
worker for subscription "sub4" has started
2025-08-13 15:13:01.482 IST [61926] LOG: logical replication worker
for subscription "sub4" resumes retaining the information for
detecting conflicts
2025-08-13 15:13:01.482 IST [61926] DETAIL: The time spent applying
changes up to LSN 0/17C9348 is now within the maximum limit of 50000
ms.

thanks
Shveta