Horton

RE: Conflict detection for update_deleted in logical replication

Zhijie Hou (Fujitsu) <houzj.fnst@fujitsu.com>

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From: "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>
To: Dilip Kumar <dilipbalaut@gmail.com>, Amit Kapila <amit.kapila16@gmail.com>
Cc: Xuneng Zhou <xunengzhou@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@lists.postgresql.org" <pgsql-hackers@lists.postgresql.org>
Date: 2025-05-26T07:16:48Z
Lists: pgsql-hackers 
On Sun, May 25, 2025 at 4:36 PM Dilip Kumar wrote:

> 
> On Sat, May 24, 2025 at 4:46 PM Amit Kapila <amit.kapila16@gmail.com>
> wrote:
> >
> > This sounds reasonable to me. Let us see what others think.
> >
> 
> I was looking into the for getting the transaction status from
> publisher, what I would assume this patch should be doing is request
> the publisher status first time, and if some transactions are still in
> commit, then we need to wait for them to get completed.  But in the
> current design its possible that while we are waiting for in-commit
> transactions to get committed the old running transaction might come
> in commit phase and then we wait for them again, is my understanding
> not correct?

Thanks for reviewing the patch. And yes, your understanding is correct.

> 
> Maybe this is very corner case that there are thousands of old running
> transaction and everytime we request the status we find some
> transactions is in commit phase and the process keep running for long
> time until all the old running transaction eventually get committed.
> 
> I am thinking can't we make it more deterministic such that when we
> get the status first time if we find some transactions that are in
> commit phase then we should just wait for those transaction to get
> committed?  One idea is to get the list of xids in commit phase and
> next time when we get the list we can just compare and in next status
> if we don't get any xids in commit phase which were in commit phase
> during previous status then we are done.  But not sure is this worth
> the complexity?  Mabe not but shall we add some comment explaining the
> case and also explaining why this corner case is not harmful?

I also think it's not worth the complexity for this corner case which is
rare. So, I have added some comments in wait_for_publisher_status() to
mention the same.

Best Regards,
Hou zj

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.