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: 2025-07-28T11:08:45Z
Lists: pgsql-hackers 
On Fri, Jul 25, 2025 at 4:38 PM Zhijie Hou (Fujitsu)
<houzj.fnst@fujitsu.com> wrote:
>
>
> The V53-0001 also includes Shveta's comments in [1].
>

Thanks, I have not yet completed the review, but please find a few
comments on 001:

1)
IsIndexUsableForFindingDeletedTuple()
We first have:
+ /*
+ * A frozen transaction ID indicates that it must fall behind the conflict
+ * detection slot.xmin.
+ */
+ if (HeapTupleHeaderXminFrozen(index_tuple->t_data))
+ return true;

thent his:
+ index_xmin = HeapTupleHeaderGetRawXmin(index_tuple->t_data);

Shall we use HeapTupleHeaderGetXmin() instead of above 2? We can check
if xid returned by HeapTupleHeaderGetXmin() is FrozenTransactionId or
normal one and then do further processing.


2)
Both FindRecentlyDeletedTupleInfoByIndex and
FindRecentlyDeletedTupleInfoSeq() has:
+ /* Exit early if the commit timestamp data is not available */
+ if (!track_commit_timestamp)
+ return false;

We shall either move this check to FindDeletedTupleInLocalRel() or in
the caller of FindDeletedTupleInLocalRel() where we check
'MySubscription->retaindeadtuples'. Moving to the caller of
FindDeletedTupleInLocalRel() looks better as there is no need to call
FindDeletedTupleInLocalRel itself if pre-conditions are not met.


3)
FindRecentlyDeletedTupleInfoSeq():
+ * during change applications. While this approach may be slow on large tables,
+ * it is considered acceptable because it is only used in rare conflict cases
+ * where the target row for an update cannot be found.
+ */
Shall we extend the last line to:
where the target row for an update cannot be found and index scan can
not be used.


4)
catalogs.sgml:
+       If true, he detection of <xref linkend="conflict-update-deleted"/> is
he --> the

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.