Horton

Re: Conflict detection for update_deleted in logical replication

Dilip Kumar <dilipbalaut@gmail.com>

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From: Dilip Kumar <dilipbalaut@gmail.com>
To: "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>
Cc: Amit Kapila <amit.kapila16@gmail.com>, shveta malik <shveta.malik@gmail.com>, vignesh C <vignesh21@gmail.com>, Masahiko Sawada <sawada.mshk@gmail.com>, Nisha Moond <nisha.moond412@gmail.com>, "Hayato Kuroda (Fujitsu)" <kuroda.hayato@fujitsu.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2025-07-03T04:56:12Z
Lists: pgsql-hackers 
On Wed, Jul 2, 2025 at 12:58 PM Zhijie Hou (Fujitsu)
<houzj.fnst@fujitsu.com> wrote:
>

> During local testing, I discovered a bug caused by my oversight in assigning
> the new xmin to slot.effective, which resulted in dead tuples remaining
> non-removable until restart. I apologize for the error and have provided
> corrected patches. Kindly use the latest patch set for performance testing.

You changes related to write barrier LGTM, however I have question
regarding below change, IIUC, in logical replication
MyReplicationSlot->effective_xmin should be the xmin value which has
been flushed to the disk, but here we are just setting "data.xmin =
new_xmin;" and marking the slot dirty so I believe its not been yet
flushed to the disk right?

+advance_conflict_slot_xmin(TransactionId new_xmin)
+{
+ Assert(MyReplicationSlot);
+ Assert(TransactionIdIsValid(new_xmin));
+ Assert(TransactionIdPrecedesOrEquals(MyReplicationSlot->data.xmin, new_xmin));
+
+ /* Return if the xmin value of the slot cannot be advanced */
+ if (TransactionIdEquals(MyReplicationSlot->data.xmin, new_xmin))
+ return;
+
+ SpinLockAcquire(&MyReplicationSlot->mutex);
+ MyReplicationSlot->effective_xmin = new_xmin;
+ MyReplicationSlot->data.xmin = new_xmin;
+ SpinLockRelease(&MyReplicationSlot->mutex);
+
+ elog(DEBUG1, "updated xmin: %u", MyReplicationSlot->data.xmin);
+
+ ReplicationSlotMarkDirty();
+ ReplicationSlotsComputeRequiredXmin(false);
..
}

-- 
Regards,
Dilip Kumar
Google

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.