Horton

Re: Conflict detection for update_deleted in logical replication

Amit Kapila <amit.kapila16@gmail.com>

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From: Amit Kapila <amit.kapila16@gmail.com>
To: "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>
Cc: "Hayato Kuroda (Fujitsu)" <kuroda.hayato@fujitsu.com>, pgsql-hackers <pgsql-hackers@postgresql.org>, shveta malik <shveta.malik@gmail.com>, vignesh C <vignesh21@gmail.com>, Nisha Moond <nisha.moond412@gmail.com>, Dilip Kumar <dilipbalaut@gmail.com>, Masahiko Sawada <sawada.mshk@gmail.com>
Date: 2025-07-25T06:33:24Z
Lists: pgsql-hackers 
On Wed, Jul 23, 2025 at 12:53 PM Zhijie Hou (Fujitsu)
<houzj.fnst@fujitsu.com> wrote:
>
> Thanks for pushing. I have rebased the remaining patches.
>

+ * This function performs a full table scan instead of using indexes because
+ * index scans could miss deleted tuples if an index has been re-indexed or
+ * re-created during change applications.

IIUC, once the tuple is not found during update, the patch does an
additional scan with SnapshotAny to find the DEAD tuple, so that it
can report update_deleted conflict, if one is found. The reason in the
comments to do sequential scan in such cases sound reasonable but I
was thinking if we can do index scans if the pg_conflict_* slot's xmin
is ahead of the RI (or any usable index that can be used during scan)
index_tuple's xmin? Note, we use a similar check with the indcheckxmin
parameter in pg_index though the purpose of that is different. If this
can happen then still in most cases the index scan will happen.

-- 
With Regards,
Amit Kapila.

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.