Horton

Re: Conflict detection for update_deleted in logical replication

vignesh C <vignesh21@gmail.com>

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From: vignesh C <vignesh21@gmail.com>
To: "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>
Cc: "Hayato Kuroda (Fujitsu)" <kuroda.hayato@fujitsu.com>, Amit Kapila <amit.kapila16@gmail.com>, Nisha Moond <nisha.moond412@gmail.com>, Masahiko Sawada <sawada.mshk@gmail.com>, shveta malik <shveta.malik@gmail.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2025-01-07T11:11:14Z
Lists: pgsql-hackers 
On Wed, 25 Dec 2024 at 08:13, Zhijie Hou (Fujitsu)
<houzj.fnst@fujitsu.com> wrote:
>
> On Monday, December 23, 2024 2:15 PM Kuroda, Hayato/黒田 隼人 <kuroda.hayato@fujitsu.com> wrote:
> >
> > Dear Hou,
> >
> > Thanks for updating the patch. Few comments:
>
> Thanks for the comments!
>
> > 02.  ErrorOnReservedSlotName()
> >
> > Currently the function is callsed from three points -
> > create_physical_replication_slot(),
> > create_logical_replication_slot() and CreateReplicationSlot().
> > Can we move them to the ReplicationSlotCreate(), or combine into
> > ReplicationSlotValidateName()?
>
> I am not sure because moving the check into these functions because that would
> prevent the launcher from creating the slot as well unless we add a new
> parameter for these functions, but I am not sure if it's worth it at this
> stage.
>
> >
> > 03. advance_conflict_slot_xmin()
> >
> > ```
> >       Assert(TransactionIdIsValid(MyReplicationSlot->data.xmin));
> > ```
> >
> > Assuming the case that the launcher crashed just after
> > ReplicationSlotCreate(CONFLICT_DETECTION_SLOT).
> > After the restart, the slot can be acquired since
> > SearchNamedReplicationSlot(CONFLICT_DETECTION_SLOT)
> > is true, but the process would fail the assert because data.xmin is still invalid.
> >
> > I think we should re-create the slot when the xmin is invalid. Thought?
>
> After thinking more, the standard approach to me would be to mark the slot as
> EPHEMERAL during creation and persist it after initializing, so changed like
> that.
>
> > 05. check_remote_recovery()
> >
> > Can we add a test case related with this?
>
> I think the code path is already tested, and I am a bit unsure if we want to setup
> a standby to test the ERROR case, so didn't add this.
>
> ---
>
> Attach the new version patch set which addressed all other comments.

I was doing backward compatibility test by creating publication in
PG17 and subscription with the patch on HEAD:
Currently, we are able to create subscription with
detect_update_deleted option for a publication on PG17:
postgres=# create subscription sub1 connection 'dbname=postgres
host=localhost port=5432' publication pub1 with
(detect_update_deleted=true);
NOTICE:  created replication slot "sub1" on publisher
CREATE SUBSCRIPTION

This should not be allowed now as the subscriber will now request
publisher status from the publisher for which handling is not
available in the publisher:
+static void
+request_publisher_status(RetainConflictInfoData *data)
+{
...
+       pq_sendbyte(request_message, 'p');
+       pq_sendint64(request_message, GetCurrentTimestamp());
...
+}

I felt this should not be allowed.

Regards,
Vignesh

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.