Horton

Re: Conflict detection for update_deleted in logical replication

Dilip Kumar <dilipbalaut@gmail.com>

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From: Dilip Kumar <dilipbalaut@gmail.com>
To: "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.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: 2025-08-01T11:41:48Z
Lists: pgsql-hackers 
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?

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.

-- 
Regards,
Dilip Kumar
Google

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.