Re: Conflict detection for update_deleted in logical replication

On Wed, Jan 15, 2025 at 9:38 AM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>
> On Wed, Jan 15, 2025 at 5:57 AM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
> >
> > Probably retaining dead tuples based on the time duration or its age
> > might be other solutions, it would increase a risk of not being able
> > to detect update_deleted conflict though. I think in any way as long
> > as we accumulate dead tulpes to detect update_deleted conflicts, it
> > would be a tradeoff between reliably detecting update_deleted
> > conflicts and the performance.
> >
>
> Right, and users have an option for it. Say, if they set max_lag as -1
> (or some special value), we won't invalidate the slot, so the
> update_delete conflict can be detected with complete reliability. At
> this stage, it is okay if this information is LOGGED and displayed via
> a system view. We need more thoughts while working on the CONFLICT
> RESOLUTION patch such as we may need to additionally display a WARNING
> or ERROR if the remote_tuples commit_time is earlier than the last
> time slot is invalidated.
>

The more reliable way to do something in this regard would be that if
there is a valid and active pg_conflict_detection (or whatever we name
this slot) then consider the update_missing conflict detected as
reliable. Otherwise, the conflict_type will depend on whether the
vacuum has removed the dead row. so, the conflict management system or
users would easily know when to rely on this update_missing conflict
type.

--
With Regards,
Amit Kapila.