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>, Masahiko Sawada <sawada.mshk@gmail.com>, shveta malik <shveta.malik@gmail.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2024-10-18T09:46:34Z
Lists: pgsql-hackers 
On Fri, Oct 11, 2024 at 2:04 PM Zhijie Hou (Fujitsu)
<houzj.fnst@fujitsu.com> wrote:
>
>
> Attach the V4 patch set which addressed above comments.
>

A few minor comments:
1.
+ * Retaining the dead tuples for this period is sufficient because any
+ * subsequent transaction from the publisher will have a later timestamp.
+ * Therefore, it is acceptable if dead tuples are removed by vacuum and an
+ * update_missing conflict is detected, as the correct resolution for the
+ * last-update-wins strategy in this case is to convert the UPDATE to an INSERT
+ * and apply it anyway.
+ *
+ * The 'remote_wal_pos' will be reset after sending a new request to walsender.
+ */
+static void
+maybe_advance_nonremovable_xid(XLogRecPtr *remote_wal_pos,
+    DeadTupleRetainPhase *phase)

We should cover the key point of retaining dead tuples which is to
avoid converting updates to inserts (considering the conflict as
update_missing) in the comments above and also in the commit message.

2. In maybe_advance_nonremovable_xid() all three phases are handled by
different if blocks but as per my understanding the phase value will
be unique in one call to the function. So, shouldn't it be handled
with else if?

-- 
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.