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: 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>, Amit Kapila <amit.kapila16@gmail.com>
Date: 2025-05-22T02:59:02Z
Lists: pgsql-hackers 
On Tue, May 20, 2025 at 11:08 AM shveta malik wrote:
> 
> Please find few more comments:

Thanks for the comments!

> 
> 2)
> 
> ----------
>   send_feedback(last_received, requestReply, requestReply);
> 
> + maybe_advance_nonremovable_xid(&data, false);
> +
>   /*
>   * Force reporting to ensure long idle periods don't lead to
>   * arbitrarily delayed stats. Stats can only be reported outside
> ----------
> 
> Why do we need this call to 'maybe_advance_nonremovable_xid' towards end
> of LogicalRepApplyLoop() i.e. the last call? Can it make any further 'data.phase'
> change here? IIUC, there are 2 triggers for 'data.phase' change through
> LogicalRepApplyLoop(). First one is for the very first time when we start this
> loop, it will set data.phase to
> 0  (RCI_GET_CANDIDATE_XID) and will call
> maybe_advance_nonremovable_xid(). After that, LogicalRepApplyLoop()
> function can trigger a 'data.phase' change only when it receives a response
> from the publisher. Shouldn't the first 4 calls  to
> maybe_advance_nonremovable_xid() from LogicalRepApplyLoop() suffice?

I think each invocation of maybe_advance_nonremovable_xid() has a chance to
complete the final RCI_WAIT_FOR_LOCAL_FLUSH phase, as it could be waiting for
changes to be flushed. The function call was added with the intention to
enhance the likelihood of advancing the transaction ID, particularly when it is
waiting for flushed changes. Although we could check the same in other func
calls as well, but I think it's OK to keep the last check.


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.