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: 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: 2025-07-01T10:09:35Z
Lists: pgsql-hackers

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On Tue, Jul 1, 2025 at 5:07 PM Dilip Kumar wrote:
> 
> On Tue, Jul 1, 2025 at 2:24 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
> >
> > On Tue, Jul 1, 2025 at 10:53 AM Dilip Kumar <dilipbalaut@gmail.com> wrote:
> > >
> > > On Tue, Jul 1, 2025 at 10:31 AM Dilip Kumar <dilipbalaut@gmail.com>
> wrote:
> > > >
> > > > On Mon, Jun 30, 2025 at 6:59 PM Zhijie Hou (Fujitsu)
> > > > <houzj.fnst@fujitsu.com> wrote:
> > > > >
> > > > > On Mon, Jun 30, 2025 at 7:22 PM Amit Kapila wrote:
> > > > > >
> > > >
> > > > I was looking at 0001, it mostly looks fine to me except this one
> > > > case.  So here we need to ensure that commits must be acquired
> > > > after marking the flag, don't you think we need to ensure strict
> > > > statement ordering using memory barrier, or we think it's not
> > > > required and if so why?
> > > >
> >
> > Good point. I also think we need a barrier here, but a write barrier
> > should be sufficient as we want ordering of two store operations.
> 
> +1
> 
> > > > RecordTransactionCommitPrepared()
> > > > {
> > > > ..
> > > > + MyProc->delayChkptFlags |= DELAY_CHKPT_IN_COMMIT;
> > > > +
> > > > + /*
> > > > + * Note it is important to set committs value after marking
> > > > + ourselves as
> > > > + * in the commit critical section (DELAY_CHKPT_IN_COMMIT). This
> > > > + is because
> > > > + * we want to ensure all transactions that have acquired commit
> > > > + timestamp
> > > > + * are finished before we allow the logical replication client to
> > > > + advance
> > > > + * its xid which is used to hold back dead rows for conflict detection.
> > > > + * See maybe_advance_nonremovable_xid.
> > > > + */
> > > > + committs = GetCurrentTimestamp();
> > > > }
> > >
> > > I'm unsure whether the function call inherently acts as a memory
> > > barrier, preventing the compiler from reordering these operations.
> > > This needs to be confirmed.
> > >
> >
> > As per my understanding, function calls won't be a memory barrier. In
> > this regard, we need a similar change in RecordTransactionCommit as
> > well.
> 
> Right, we need this in RecordTransactionCommit() as well.

Thanks for the comments! I also agree that the barrier is needed.

Here is V45 patch set.

I modified 0001, added write barriers, and improved some comments.

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.