RE: Conflict detection for update_deleted in logical replication

On Thursday, August 7, 2025 8:35 PM Dilip Kumar <dilipbalaut@gmail.com> wrote:
> On Mon, Aug 4, 2025 at 3:11 PM Amit Kapila <amit.kapila16@gmail.com>
> wrote:
> >
> > On Mon, Aug 4, 2025 at 11:46 AM shveta malik <shveta.malik@gmail.com>
> wrote:
> > >
> > > 7)
> > > Shall we rename 'max_conflict_retention_duration' to
> > > 'max_conflict_info_retention_duration' as the latter one is more
> > > clear?
> > >
> >
> > Before bikeshedding on the name of this option, I would like us to
> > once again consider whether we should provide this option at
> > subscription-level or GUC?
> >
> > The rationale behind considering it as a subscription option is that
> > the different subscriptions may have different requirements for dead
> > tuple retention which means that for some particular subscription, the
> > workload may not be always high which means that even if temporarily
> > the lag_duration (of apply) has exceeded the new option's value, it
> > should become okay. So, in such a case users may not want to configure
> > max_conflict_retention_duration for a subscription which would
> > otherwise lead to stop detection of update_deleted conflict for that
> > subscription.
> 
> Yes valid point, and it's also possible that for some subscription user is okay to
> not retain dead tuple if it crosses certain duration OTOH for some subscription
> it is too critical to retain dead tuple even if user has to take some performance
> hit, so might want to have higher threshold for those slots.
> 
> > The other point is that it is only related to the retain_dead_tuples
> > option of the subscription, so providing this new option at the same
> > level would appear consistent.
> 
> Yes that's a valid argument, because if the user is setting retain dead tuples for
> subscription then only they need to consider setting duration.
> 
> > I remember that previously Sawada-San has advocated it to provide as
> > GUC but I think the recent tests suggest that users should define
> > pub-sub topology carefuly to enable retain_dead_tuples option as even
> > mentioned in docs[2], so, it is worth considering to provide it at
> > subscription-level.
> 
> IMHO, it should be fine to provide the subscription option first and if we see
> complaints about inconvenience we may consider GUC as well in the future.

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.

Best Regards,
Hou zj