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: 2025-07-01T05:23:40Z
Lists: pgsql-hackers 
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?
>
> 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.


-- 
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.