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: Xuneng Zhou <xunengzhou@gmail.com>
Cc: "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.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>, Amit Kapila <amit.kapila16@gmail.com>, pgsql-hackers@lists.postgresql.org
Date: 2025-05-24T04:34:25Z
Lists: pgsql-hackers 
On Fri, May 23, 2025 at 9:21 PM Xuneng Zhou <xunengzhou@gmail.com> wrote:
>
Looking at v31-0001 again, most of it looks fine except this logic of
getting the commit_ts after marking the transaction in commit.  I see
in RecordTransactionCommit(), we are setting this flag
(DELAY_CHKPT_IN_COMMIT) to put the transaction in commit state[1], and
after that we insert the commit log[2], but I noticed that there we
call GetCurrentTransactionStopTimestamp() for acquiring the commit-ts
and IIUC we want to ensure that commit-ts timestamp should be after we
set the transaction in commit with (DELAY_CHKPT_IN_COMMIT), but
question is, is it guaranteed that the place we are calling
GetCurrentTransactionStopTimestamp() will always give us the current
timestamp? Because if you see this function, it may return
'xactStopTimestamp' as well if that is already set.  I am still
digging a bit more. Is there a possibility that 'xactStopTimestamp' is
already set during some interrupt handling when
GetCurrentTransactionStopTimestamp() is already called by
pgstat_report_stat(), or is it guaranteed that during
RecordTransactionCommit we will call this first time?

If we have already ensured this then I think adding a comment to
explain the same will be really useful.

[1]
@@ -1537,7 +1541,7 @@ RecordTransactionCommit(void)
  */
  if (markXidCommitted)
  {
- MyProc->delayChkptFlags &= ~DELAY_CHKPT_START;
+ MyProc->delayChkptFlags &= ~DELAY_CHKPT_IN_COMMIT;
  END_CRIT_SECTION();
  }

[2]
/*
* Insert the commit XLOG record.
*/
XactLogCommitRecord(GetCurrentTransactionStopTimestamp(),
                                       nchildren, children, nrels, rels,
                                       ndroppedstats, droppedstats,
                                       nmsgs, invalMessages,
                                       RelcacheInitFileInval,
                                       MyXactFlags,
                                       InvalidTransactionId, NULL /*
plain commit */ );

-- 
Regards,
Dilip Kumar
EnterpriseDB: http://www.enterprisedb.com

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.