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: 2025-05-22T02:58:42Z
Lists: pgsql-hackers 
On Tue, May 20, 2025 at 6:30 PM shveta malik wrote:
> 
> Few more comments mostly for patch001:

Thanks for the comments!

> 
> 4)
> For this feature, since we are only interested in remote UPDATEs happening
> concurrently, so shall we ask primary to provide oldest "UPDATE"
> transaction-id in commit-phase rather than any operation's transaction-id?
> This may avoid unnecessarily waiting and pinging at subscriber's end in order
> to advance oldest_nonremovable-xid.
> Thoughts?

It is possible, but considering the potential complexity/cost to track UPDATE
operations in top-level and sub-transactions, coupled with its limited benefit
for workloads featuring frequent UPDATEs on publishers such as observed during
TPC-B performance tests, I have opted to document this possibility in comments
instead of implementing it in the patch set.

> 
> 5)
> +
> +/*
> + * GetOldestTransactionIdInCommit()
> + *
> + * Similar to GetOldestActiveTransactionId but returns the oldest
> transaction ID
> + * that is currently in the commit phase.
> + */
> +TransactionId
> +GetOldestTransactionIdInCommit(void)
> 
> If there is no transaction currently in 'commit' phase, this function will then
> return the next transaction-id. Please mention this in the comments. I think the
> doc 'protocol-replication.html' should also be updated for the same.

I added this info in the doc. But since we have merged this function with
GetOldestActiveTransactionId() which has the same behavior, so I am
not adding more code comments for the existing function.

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.