Horton

Re: Conflict detection for update_deleted in logical replication

shveta malik <shveta.malik@gmail.com>

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From: shveta malik <shveta.malik@gmail.com>
To: Amit Kapila <amit.kapila16@gmail.com>
Cc: "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.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>, Dilip Kumar <dilipbalaut@gmail.com>, Masahiko Sawada <sawada.mshk@gmail.com>, shveta malik <shveta.malik@gmail.com>
Date: 2025-07-25T13:54:25Z
Lists: pgsql-hackers 
On Fri, Jul 25, 2025 at 2:31 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
>
> On Fri, Jul 25, 2025 at 12:37 PM shveta malik <shveta.malik@gmail.com> wrote:
> >
> > On Thu, Jul 24, 2025 at 9:12 AM shveta malik <shveta.malik@gmail.com> wrote:
> > >
> > >
> > > 2)
> > > +               if (MySubscription->retaindeadtuples &&
> > > +                       FindMostRecentlyDeletedTupleInfo(localrel, remoteslot,
> > > +
> > >                   &conflicttuple.xmin,
> > > +
> > >                   &conflicttuple.origin,
> > > +
> > >                   &conflicttuple.ts) &&
> > > +                       conflicttuple.origin != replorigin_session_origin)
> > > +                       type = CT_UPDATE_DELETED;
> > > +               else
> > > +                       type = CT_UPDATE_MISSING;
> > >
> > > Shall the conflict be detected as update_deleted irrespective of origin?
> > >
> >
> > On thinking more here, I think that we may have the possibility of
> > UPDATE after DELETE from the same origin only when a publication
> > selectively publishes certain operations.
> >
> > 1)
> > Consider a publication that only publishes UPDATE and DELETE
> > operations. On the publisher, we may perform operations like DELETE,
> > INSERT, and UPDATE. On the subscriber, only DELETE and UPDATE events
> > are received. In this case, should we treat the incoming UPDATE as
> > update_deleted or update_missing?
> >
>
> If the user is doing subscription only for certain operations like
> Update or Delete, she may not be interested in eventual consistency as
> some of the data may not be replicated, so a conflict detection
> followed by any resolution may not be helpful.
>
> The other point is that if we report update_delete in such cases, it
> won't be reliable, sometimes it can be update_missing as vacuum would
> have removed the row, OTOH, if we report update_missing, it will
> always be the same conflict, and we can document it.
>

Agree with both the points. We can keep the current behaviour as it is.

thanks
Shveta

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.