Horton

Re: Synchronizing slots from primary to standby

Peter Smith <smithpb2250@gmail.com>

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From: Peter Smith <smithpb2250@gmail.com>
To: "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>
Cc: "Drouvot, Bertrand" <bertranddrouvot.pg@gmail.com>, shveta malik <shveta.malik@gmail.com>, Amit Kapila <amit.kapila16@gmail.com>, "Hayato Kuroda (Fujitsu)" <kuroda.hayato@fujitsu.com>, Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>, Peter Eisentraut <peter.eisentraut@enterprisedb.com>, Bruce Momjian <bruce@momjian.us>, Ashutosh Sharma <ashu.coek88@gmail.com>, Andres Freund <andres@anarazel.de>, pgsql-hackers <pgsql-hackers@postgresql.org>, Ajin Cherian <itsajin@gmail.com>, Alvaro Herrera <alvherre@alvh.no-ip.org>
Date: 2023-11-30T07:05:29Z
Lists: pgsql-hackers 
Here are some review comments for v41-0001.

======
doc/src/sgml/ref/alter_subscription.sgml

1.
+     <para>
+      When altering the
+      <link linkend="sql-createsubscription-params-with-slot-name"><literal>slot_name</literal></link>,
+      the <literal>failover</literal> property of the new slot may
differ from the
+      <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>
+      parameter specified in the subscription, you need to adjust the
+      <literal>failover</literal> property when creating the slot so that it
+      matches the value specified in subscription.
+     </para>

For the second part a) it should be a separate sentence, and b) IMO
you are not really "adjusting" something if you are "creating" it.

SUGGESTION
When altering the slot_name, the failover property of the new slot may
differ from the failover parameter specified in the subscription. When
creating the slot  ensure the slot failover property matches the
failover parameter value of the subscription.

======
src/backend/catalog/pg_subscription.c

2. AlterSubscription

+ if (sub->failoverstate == LOGICALREP_FAILOVER_STATE_ENABLED && opts.copy_data)
+ ereport(ERROR,
+ (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+ errmsg("ALTER SUBSCRIPTION with refresh and copy_data is not allowed
when failover is enabled"),

This is another example where the "two_phase" and "failover" should be
extracted to make a common message for the translator.

(Already posted this comment before -- see [1] #13)

~~~

3.
+ /*
+ * See comments above for twophasestate, same holds true for
+ * 'failover'
+ */
+ if (sub->failoverstate == LOGICALREP_FAILOVER_STATE_ENABLED && opts.copy_data)
+ ereport(ERROR,
+ (errcode(ERRCODE_SYNTAX_ERROR),
+ errmsg("ALTER SUBSCRIPTION ... REFRESH with copy_data is not allowed
when failover is enabled"),
+ errhint("Use ALTER SUBSCRIPTION ... REFRESH with copy_data = false,
or use DROP/CREATE SUBSCRIPTION.")));

This is another example where the "two_phase" and "failover" should be
extracted to make a common message for the translator.

(Already posted this comment before -- see [1] #14)

======
src/backend/replication/walsender.c

4.
+/*
+ * Wake up logical walsenders with failover-enabled slots if the physical slot
+ * of the current walsender is specified in standby_slot_names GUC.
+ */
+void
+PhysicalWakeupLogicalWalSnd(void)

Is it better to refer to "walsender processes" being woken instead of
just walsenders?

e.g.
"Wake up logical walsenders..." --> "Wake up the logical walsender processes..."

======
[1] v35-0001 review.
https://www.postgresql.org/message-id/CAHut%2BPv-yu71ogj_hRi6cCtmD55bsyw7XTxj1Nq8yVFKpY3NDQ%40mail.gmail.com

Kind Regards,
Peter Smith.
Fujitsu Australia

Commits

  1. Doc: Add the new section "Logical Replication Failover".

  2. Fix the review comments and a bug in the slot sync code.

  3. Fix a test in failover slots regression test.

  4. Fix the intermittent buildfarm failures in 040_standby_failover_slots_sync.

  5. Split XLogCtl->LogwrtResult into separate struct members

  6. Ensure that the sync slots reach a consistent state after promotion without losing data.

  7. Introduce a new GUC 'standby_slot_names'.

  8. Fix BF failure introduced by commit b3f6b14cf4.

  9. Fixups for commit 93db6cbda0.

  10. Fix BF failure in commit 93db6cbda0.

  11. Add a new slot sync worker to synchronize logical slots.

  12. Improve ERROR/LOG messages added by commits ddd5f4f54a and 7a424ece48.

  13. Disable autovacuum on primary in 040_standby_failover_slots_sync test.

  14. Fix the incorrect format specifier used in commit 7a424ece48.

  15. Change the LOG level in 040_standby_failover_slots_sync.pl to DEBUG2.

  16. Add more LOG and DEBUG messages for slot synchronization.

  17. Another try to fix BF failure introduced in commit ddd5f4f54a.

  18. Fix BF introduced in commit ddd5f4f54a.

  19. Add a slot synchronization function.

  20. Clean-ups for 776621a5e4 and 7329240437.

  21. Enhance libpqrcv APIs to support slot synchronization.

  22. Add a failover option to subscriptions.

  23. Allow setting failover property in the replication command.

  24. Allow to enable failover property for replication slots via SQL API.

  25. Add macros for looping through a List without a ListCell.

  26. Track conflict_reason in pg_replication_slots.

  27. Allow upgrades to preserve the full subscription's state.

  28. Add support for incremental backup.

  29. Simplify some logic in CreateReplicationSlot()

  30. Fix uninitialized access to InitialRunningXacts during decoding after ERROR.

  31. Flexible options for CREATE_REPLICATION_SLOT.

  32. Empty search_path in logical replication apply worker and walsender.

  33. Fix oldest xmin and LSN computation across repslots after advancing

  34. Require C99 (and thus MSCV 2013 upwards).