Re: Conflict detection for update_deleted in logical replication

On Mon, Aug 4, 2025 at 3:11 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>
> On Mon, Aug 4, 2025 at 11:46 AM shveta malik <shveta(dot)malik(at)gmail(dot)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.

--
Regards,
Dilip Kumar
Google