RE: Conflict detection for update_deleted in logical replication

On Tuesday, August 12, 2025 4:37 PM shveta malik <shveta.malik@gmail.com> wrote:
> 
> On Mon, Aug 11, 2025 at 2:40 PM Zhijie Hou (Fujitsu)
> <houzj.fnst@fujitsu.com> wrote:
> >
> > I agree. So, following the above points and some off-list discussions,
> > I have revised the option to be a subscription option in the V60 version.
> >
> 
> Thank You for the patches. Tried to test the new sub-level parameter, have few
> comments:

Thanks for the comments.

> 
> 1)
> Let's say commit on pub is taking time and worker has stopped retention and
> meanwhile we alter max_conflict_retention_duration=0,
> then the expectation is immediately worker should resume retention.
> But it does not happen, it does not restart conflict-retention until the pub's
> commit is finished. The 'dead_tuple_retention_active'
> remains 'f' till then.
> 
> postgres=# select subname, subretaindeadtuples, maxconflretention from
> pg_subscription order by subname;  subname | subretaindeadtuples |
> maxconflretention
> ---------+---------------------+-------------------
>  sub1       | t                                |                 0
> 
> 
> postgres=# select subname, worker_type, dead_tuple_retention_active from
> pg_stat_subscription order by subname;  subname | worker_type |
> dead_tuple_retention_active
> ---------+-------------+-----------------------------
>  sub1      | apply              | f
> 
> I think we shall reset 'stop_conflict_info_retention' flag in
> should_stop_conflict_info_retention() if maxconflretention is 0 and the flag is
> originally true.

Agreed. Thinking more, I think we can resume retention at more places, as in
each phase, we could have a possibility of resuming, so changed.

> 2)
> postgres=# create subscription sub2  connection 'dbname=postgres
> host=localhost user=shveta port=5433' publication pub2 WITH
> (retain_dead_tuples = false, max_conflict_retention_duration=1000);
> NOTICE:  created replication slot "sub2" on publisher CREATE
> SUBSCRIPTION
> 
> Shall we give notice that max_conflict_retention_duration is ignored as
> retain_dead_tuples is false.

Agreed. In addition to this command, I added the NOTICE for all
the cases when the max_conflict_retention_duration is ineffective as 
discussed[1].


> 
> 3)
> When worker stops retention, it gives message:
> 
> LOG:  logical replication worker for subscription "sub1" will stop retaining the
> information for detecting conflicts
> DETAIL:  The time spent advancing the non-removable transaction ID has
> exceeded the maximum limit of 100 ms.
> 
> Will it be more informative if we mention the parameter name
> 'max_conflict_retention_duration' either in DETAIL or in additional HINT, as
> then the user can easily map this behaviour to the parameter configured.

Added.

Here is the V61 patch set which addressed above comments and the comment by Nisha[2].

[1] https://www.postgresql.org/message-id/CAJpy0uC81YgAmrA2ji2ZKbJK_qfvajuV6%3DyvcCWuFsQKqiED%2BA%40mail.gmail.com
[2] https://www.postgresql.org/message-id/CABdArM7G1sSDDOEC-nmJRnJMCZoBsLqOMz08UotX_h_wqxHWCg%40mail.gmail.com

Best Regards,
Hou zj