RE: Conflict detection for update_deleted in logical replication

On Friday, August 1, 2025 7:42 PM Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
>
> On Fri, Aug 1, 2025 at 5:02 PM Zhijie Hou (Fujitsu) <houzj(dot)fnst(at)fujitsu(dot)com>
> wrote:
> >
> > > 2.
> > >
> > > + If set to <literal>true</literal>, the detection of
> > > + <xref linkend="conflict-update-deleted"/> is enabled, and
> > > + a
> > > physical
> > > + replication slot named
> > > <quote><literal>pg_conflict_detection</literal></quote>
> > > created on the subscriber to prevent the conflict information
> from
> > > being removed.
> > >
> > > "to prevent the conflict information from being removed." should be
> > > rewritten as "to prevent removal of tuple required for conflict detection"
> >
> > It appears the document you commented is already committed. I think
> > the intention was to make a general statement that neither dead tuples
> > nor commit timestamp data would be removed.
>
> Okay got it, so instead of "conflict information" should we say "information for
> detecting conflicts" or "conflict detection information", conflict information
> looks like we want to prevent the information about the conflict which has
> already happened, instead we are preventing information which are required
> for detecting the conflict, does this make sense?

It makes sense to me, so changed.

>
> I know this is already committed, but actually this is part of the whole patch set
> so we can always improvise it.
>
> > >
> > > 3.
> > > + /* Return if the commit timestamp data is not available */
> > > + if (!track_commit_timestamp)
> > > + return false;
> > >
> > > Shouldn't caller should take care of this? I mean if the
> > > 'retaindeadtuples' and 'track_commit_timestamp' is not set then
> > > caller shouldn't even call this function.
> >
> > I feel moving the checks into a single central function would
> > streamline the caller, reducing code duplication. So, maybe we could
> > move the retaindeadtuple check into this function as well for consistency.
> Thoughts ?
>
> Fine with either way, actually I wanted both the check 'retaindeadtuple' and
> 'track_commit_timestamp' at the same place.

Thanks for confirming. Here is V56 patch set which addressed all the
comments including the comments from Amit[1] and Shveta[2].

I have merged V55-0002 into 0001 and updated the list of author
and reviewers based on my knowledge.

[1] https://www.postgresql.org/message-id/CAA4eK1%2B2tZ0rGowwpfmPQA03KdBOaeaK6D5omBN76UTP2EPx6w%40mail.gmail.com
[2] https://www.postgresql.org/message-id/CAJpy0uDNhP%2BQeH-zGLBgMnRY1JZGVeoZ_dxff5S6HmpnRcWk8A%40mail.gmail.com

Best Regards,
Hou zj