Horton

RE: Conflict detection for update_deleted in logical replication

Zhijie Hou (Fujitsu) <houzj.fnst@fujitsu.com>

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From: "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>
To: Dilip Kumar <dilipbalaut@gmail.com>
Cc: Amit Kapila <amit.kapila16@gmail.com>, shveta malik <shveta.malik@gmail.com>, "Hayato Kuroda (Fujitsu)" <kuroda.hayato@fujitsu.com>, pgsql-hackers <pgsql-hackers@postgresql.org>, vignesh C <vignesh21@gmail.com>, Nisha Moond <nisha.moond412@gmail.com>, Masahiko Sawada <sawada.mshk@gmail.com>
Date: 2025-08-01T15:46:08Z
Lists: pgsql-hackers

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On Friday, August 1, 2025 7:42 PM Dilip Kumar <dilipbalaut@gmail.com> wrote:
> 
> On Fri, Aug 1, 2025 at 5:02 PM Zhijie Hou (Fujitsu) <houzj.fnst@fujitsu.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

Commits

  1. Fix intermittent BF failures in 035_conflicts.

  2. Resume conflict-relevant data retention automatically.

  3. Fix intermittent test failure introduced in 6456c6e2c4.

  4. Fix Coverity issue reported in commit a850be2fe.

  5. Add test to prevent premature removal of conflict-relevant data.

  6. Post-commit review fixes for 228c370868.

  7. Add max_retention_duration option to subscriptions.

  8. Detect and report update_deleted conflicts.

  9. Preserve conflict-relevant data during logical replication.

  10. Integrate FullTransactionIds deeper into two-phase code

  11. Improve checks for GUC recovery_target_timeline

  12. Prevent excessive delays before launching new logrep workers.

  13. Keep WAL segments by slot's last saved restart LSN

  14. Rework some code handling pg_subscription data in psql and pg_dump

  15. Use generateClonedIndexStmt to propagate CREATE INDEX to partitions.