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: shveta malik <shveta.malik@gmail.com>
Cc: Amit Kapila <amit.kapila16@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: 2025-06-12T06:04:41Z
Lists: pgsql-hackers

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On Wed, Jun 11, 2025 at 5:34 PM shveta malik wrote:
> 
> On Tue, Jun 10, 2025 at 11:55 AM Zhijie Hou (Fujitsu)
> <houzj.fnst@fujitsu.com> wrote:
> >
> > Here is the V35 patch set which includes the following changes:
> >
> 
> Thank You for the patches, few comments:

Thanks for the comments!

> 
> 1)
> compute_min_nonremovable_xid:
> 
> + /*
> + * Stop advancing xmin if an invalid non-removable transaction ID is
> + * found, otherwise update xmin.
> + */
> + if (!TransactionIdIsValid(nonremovable_xid))
> + *can_advance_xmin = false;
> 
> IMO, we can not have invalid nonremovable_xid here. It may be a possibility in
> a later patch where we do stop-conflict-detection for a worker and resets
> nonremovable_xid to Invalid. But in patch003, should this rather be an Assert
> as we want to ensure that worker's oldest is set to slot's-xmin by this time.

Agreed. I have removed the check and added an Assert.

> 
> 2)
> postgres=# create subscription sub1  connection 'dbname=postgres
> host=localhost user=shveta port=5433' publication pub1 WITH
> (retain_conflict_info = true);
> NOTICE:  deleted rows will continue to accumulate for detecting conflicts
> until the subscription is enabled
> NOTICE:  created replication slot "sub1" on publisher CREATE
> SUBSCRIPTION
> 
> postgres=# alter subscription sub2 enable;
> NOTICE:  deleted rows will continue to accumulate for detecting conflicts
> until the subscription is enabled
> 
> We should not have this 'NOTICE:  deleted rows' in above 2 commands.

Agreed, It was a miss. After thinking more, I have modified the patch to report
the NOTICE only when altering the retain_conflict_info for disabled
subscription as that aligns with the original intent for introducing the
NOTICE.

> 
> 
> 3)
> +
> +ALTER SUBSCRIPTION regress_testsub SET (slot_name = NONE); DROP
> +SUBSCRIPTION regress_testsub;
> 
> Shall we enable regress_testsub as well before we drop it to catch unexpected
> notices/warnings if any?

I have added the ENABLE test in the tap-test in 0005, because we do not have a
valid connection for subscriptions created in subscription.sql, So enabling the
sub here could cause network error with random socket info, making the test
unstable.

> 
> 
> 4)
> postgres=# alter subscription sub2 disable;
> WARNING:  commit timestamp and origin data required for detecting conflicts
> won't be retained
> HINT:  Consider setting "track_commit_timestamp" to true.
> 
> Do we need "track_commit_timestamp" related WARNING while disabling rci
> sub as well? I feel it should be there while enabling it alone.

Changed as suggested.

Here is the V35 patch set which includes the following changes:

0001:
Merged original V35-0001 and 0002.

0002:
* Addressed the comments above.
* The launcher will now attempt to acquire the conflict detection slot
  initially, allowing us to determine its existence by checking if
  MyReplicationSlot is NULL.
* Merged the top-up patch provided by Amit[1].

0003:
Rebased

0004:
Rebased

0005:
Added few tests to verify the WANRINGs and NOTCE.

0006:
Rebased

0007:
Rebased

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.