Re: Conflict detection for update_deleted in logical replication

On Fri, May 16, 2025 at 12:01 PM shveta malik <shveta(dot)malik(at)gmail(dot)com> wrote:
>
> On Fri, May 16, 2025 at 11:15 AM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> >
> >
> > BTW, another related point is that when we decide to stop retaining
> > dead tuples (via should_stop_conflict_info_retention), should we also
> > consider the case that the apply worker didn't even try to get the
> > publisher status because previously it decided that
> > oldest_nonremovable_xid cannot be advanced due to its
> > OldestActiveTransactionId?
> >
>
> Do you mean avoid stop-conflict-retention in such a case as apply
> worker itself did not request status from the publisher? If I
> understood your point correctly, then we can do that by advancing the
> timer to a new value even if we did not update candidate-xid and did
> not ask the status from the publisher.
>

But candidate_xid_time is also used in wait_for_local_flush() to check
clock_skew between publisher and subscriber, so for that purpose, it
is better to set it along with candidate_xid. However, can't we rely
on the valid value of candidate_xid to ensure that apply worker didn't
send any request? Note that we always reset candidate_xid once we have
updated oldest_nonremovable_xid.

--
With Regards,
Amit Kapila.