Horton

Re: Conflict detection for update_deleted in logical replication

shveta malik <shveta.malik@gmail.com>

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From: shveta malik <shveta.malik@gmail.com>
To: Dilip Kumar <dilipbalaut@gmail.com>
Cc: "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>, Amit Kapila <amit.kapila16@gmail.com>, Masahiko Sawada <sawada.mshk@gmail.com>, "Hayato Kuroda (Fujitsu)" <kuroda.hayato@fujitsu.com>, pgsql-hackers <pgsql-hackers@postgresql.org>, vignesh C <vignesh21@gmail.com>, Nisha Moond <nisha.moond412@gmail.com>, shveta malik <shveta.malik@gmail.com>
Date: 2025-08-12T09:59:22Z
Lists: pgsql-hackers 
On Tue, Aug 12, 2025 at 3:22 PM Dilip Kumar <dilipbalaut@gmail.com> wrote:
>
> On Tue, Aug 12, 2025 at 3:02 PM Zhijie Hou (Fujitsu)
> <houzj.fnst@fujitsu.com> wrote:
> >
> > On Tuesday, August 12, 2025 5:01 PM Dilip Kumar <dilipbalaut@gmail.com> wrote:
> >
> > Hi,
> >
> > >
> > > On Tue, Aug 12, 2025 at 2:21 PM Amit Kapila <amit.kapila16@gmail.com>
> > > wrote:
> > > >
> > > > On Tue, Aug 12, 2025 at 2:06 PM shveta malik <shveta.malik@gmail.com>
> > > wrote:
> > > > >
> > > > > 2)
> > > > > postgres=# create subscription sub2  connection 'dbname=postgres
> > > > > host=localhost user=shveta port=5433' publication pub2 WITH
> > > > > (retain_dead_tuples = false, max_conflict_retention_duration=1000);
> > > > > NOTICE:  created replication slot "sub2" on publisher CREATE
> > > > > SUBSCRIPTION
> > > > >
> > > > > Shall we give notice that max_conflict_retention_duration is ignored
> > > > > as retain_dead_tuples is false.
> > > > >
> > > >
> > > > How about disallowing this combination?
> > >
> > > +1 to disallow that.
> >
> > I think disallowing this case may not suffice, as users could initially set
> > (retain_dead_tuples=on, max_conflict_retention_duration=100) but later disable
> > retain_dead_tuples. This would result in the same state as
> > (retain_dead_tuples=off, max_conflict_retention_duration=100) unless we disallow
> > disabling rdt in this case as well.
> >
> > So, do you think we should disallow both cases, or we only disallow setting
> > max_conflict_retention_duration for disabled retain_dead_tuples and give NOTICE
> > in another case ?
> >
> > I personally prefer a consistent behavior, e.g., either we allow both cases and
> > give NOTICEs, or we disallow both cases. This is because, if the goal here to
> > prevent potential misconfigurations by users, the scenario where a user disables
> > retain_dead_tuples might also be considered a similar misconfiguration. So, I'm
> > a bit concerned that the benefits of imposing a partial restriction may not
> > outweigh the risk of generating inconsistent behavior. (And I did not see
> > similar precedent).
>
> I think setting 'retain_dead_tuples' to off should implicitly reset
> 'max_conflict_retention_duration', yeah but someone may argue if we
> again set 'retain_dead_tuples' to on then we should set
> 'max_conflict_retention_duration' to its original value and that could
> add an extra complexity.

I have the exact same opinion here.

>
> So maybe after thinking again IMHO, we can just go with the current
> behavior, like we allow max_conflict_retention_duration to be set to a
> positive value without setting retain_dead_tuples and issue a NOTICE
> (in both cases).
>

I feel that displaying a NOTICE in all such commands where
'max_conflict_retention_duration' will have no meaning is good enough.

thanks
Shveta

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.