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: "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>
Cc: Amit Kapila <amit.kapila16@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>, Dilip Kumar <dilipbalaut@gmail.com>, Masahiko Sawada <sawada.mshk@gmail.com>, shveta malik <shveta.malik@gmail.com>
Date: 2025-07-25T07:06:59Z
Lists: pgsql-hackers 
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?

2)
Another topology could be:
pub1 --> pub2 --> sub (origin=any)
pub1 --> sub

- pub1 publishing only DELETEs to pub2 and the same are published to
sub.
- pub1 publishing only UPDATEs to sub.

Now, consider that on pub1, an UPDATE occurs first, followed by a
DELETE. But on the sub, the events are received in reverse order:
DELETE arrives before UPDATE. Since both operations originated from
the same source (pub1), how delayed UPDATE's conflict should be
interpreted? Should it be detected as update_deleted or
update_missing? Logically, since the DELETE is the more recent
operation, it should be the final one and UPDATE should be ignored.
But if we detect it as update_missing, we might incorrectly apply the
UPDATE.
Thoughts?

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.