Re: Conflict detection for update_deleted in logical replication

On Tue, Aug 12, 2025 at 3:22 PM Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
>
> On Tue, Aug 12, 2025 at 3:02 PM Zhijie Hou (Fujitsu)
> <houzj(dot)fnst(at)fujitsu(dot)com> wrote:
> >
> > On Tuesday, August 12, 2025 5:01 PM Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
> >
> > Hi,
> >
> > >
> > > On Tue, Aug 12, 2025 at 2:21 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>
> > > wrote:
> > > >
> > > > On Tue, Aug 12, 2025 at 2:06 PM shveta malik <shveta(dot)malik(at)gmail(dot)com>
> > > wrote:
> > > > >
> > > > > 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.
> > > > >
> > > >
> > > > How about disallowing this combination?
> > >
> > > +1 to disallow that.
> >
> > I think disallowing this case may not suffice, as users could initially set
> > (retain_dead_tuples=on, max_conflict_retention_duration=100) but later disable
> > retain_dead_tuples. This would result in the same state as
> > (retain_dead_tuples=off, max_conflict_retention_duration=100) unless we disallow
> > disabling rdt in this case as well.
> >
> > So, do you think we should disallow both cases, or we only disallow setting
> > max_conflict_retention_duration for disabled retain_dead_tuples and give NOTICE
> > in another case ?
> >
> > I personally prefer a consistent behavior, e.g., either we allow both cases and
> > give NOTICEs, or we disallow both cases. This is because, if the goal here to
> > prevent potential misconfigurations by users, the scenario where a user disables
> > retain_dead_tuples might also be considered a similar misconfiguration. So, I'm
> > a bit concerned that the benefits of imposing a partial restriction may not
> > outweigh the risk of generating inconsistent behavior. (And I did not see
> > similar precedent).
>
> I think setting 'retain_dead_tuples' to off should implicitly reset
> 'max_conflict_retention_duration', yeah but someone may argue if we
> again set 'retain_dead_tuples' to on then we should set
> 'max_conflict_retention_duration' to its original value and that could
> add an extra complexity.

I have the exact same opinion here.

>
> So maybe after thinking again IMHO, we can just go with the current
> behavior, like we allow max_conflict_retention_duration to be set to a
> positive value without setting retain_dead_tuples and issue a NOTICE
> (in both cases).
>

I feel that displaying a NOTICE in all such commands where
'max_conflict_retention_duration' will have no meaning is good enough.

thanks
Shveta