Horton

Re: Synchronizing slots from primary to standby

Peter Smith <smithpb2250@gmail.com>

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From: Peter Smith <smithpb2250@gmail.com>
To: shveta malik <shveta.malik@gmail.com>
Cc: Amit Kapila <amit.kapila16@gmail.com>, "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>, Bertrand Drouvot <bertranddrouvot.pg@gmail.com>, Ajin Cherian <itsajin@gmail.com>, Masahiko Sawada <sawada.mshk@gmail.com>, Dilip Kumar <dilipbalaut@gmail.com>, Nisha Moond <nisha.moond412@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>, Alvaro Herrera <alvherre@alvh.no-ip.org>
Date: 2024-01-31T01:57:24Z
Lists: pgsql-hackers 
Hi,

I saw that v73-0001 was pushed, but it included some last-minute
changes that I did not get a chance to check yesterday.

Here are some review comments for the new parts of that patch.

======
doc/src/sgml/ref/create_subscription.sgml

1.
connect (boolean)

    Specifies whether the CREATE SUBSCRIPTION command should connect
to the publisher at all. The default is true. Setting this to false
will force the values of create_slot, enabled, copy_data, and failover
to false. (You cannot combine setting connect to false with setting
create_slot, enabled, copy_data, or failover to true.)

~

I don't think the first part "Setting this to false will force the
values ... failover to false." is strictly correct.

I think is correct to say all those *other* properties (create_slot,
enabled, copy_data) are forced to false because those otherwise have
default true values. But the 'failover' has default false, so it
cannot get force-changed at all because you can't set connect to false
when failover is true as the second part ("You cannot combine...")
explains.

IMO remove 'failover' from that first sentence.

~~~

2.
          <para>
           Since no connection is made when this option is
           <literal>false</literal>, no tables are subscribed. To initiate
           replication, you must manually create the replication slot, enable
-          the subscription, and refresh the subscription. See
+          the failover if required, enable the subscription, and refresh the
+          subscription. See
           <xref
linkend="logical-replication-subscription-examples-deferred-slot"/>
           for examples.
          </para>

IMO "see the failover if required" is very vague. See what failover?
The slot property failover, or the subscription option failover? And
"see" it for what purpose?

I think the intention was probably to say something like "ensure the
manually created slot has the same matching failover property value as
the subscriber failover option", but that is not clear from the
current text.

======
doc/src/sgml/ref/pg_dump.sgml

3.
    dump can be restored without requiring network access to the remote
    servers.  It is then up to the user to reactivate the subscriptions in a
    suitable way.  If the involved hosts have changed, the connection
-   information might have to be changed.  It might also be appropriate to
+   information might have to be changed.  If the subscription needs to
+   be enabled for
+   <link linkend="sql-createsubscription-params-with-failover"><literal>failover</literal></link>,
+   then same needs to be done by executing
+   <link linkend="sql-altersubscription-params-set">
+   <literal>ALTER SUBSCRIPTION ... SET(failover = true)</literal></link>
+   after the slot has been created.  It might also be appropriate to

"then same needs to be done" (English?)

BEFORE
If the subscription needs to be enabled for failover, then same needs
to be done by executing ALTER SUBSCRIPTION ... SET(failover = true)
after the slot has been created.

SUGGESTION
If the subscription needs to be enabled for failover, execute ALTER
SUBSCRIPTION ... SET(failover = true) after the slot has been created.

======
src/backend/commands/subscriptioncmds.c

4.
 #define SUBOPT_RUN_AS_OWNER 0x00001000
-#define SUBOPT_LSN 0x00002000
-#define SUBOPT_ORIGIN 0x00004000
+#define SUBOPT_FAILOVER 0x00002000
+#define SUBOPT_LSN 0x00004000
+#define SUBOPT_ORIGIN 0x00008000
+

A spurious blank line was added.

======
src/bin/pg_upgrade/t/004_subscription.pl

5.
-# The subscription's running status should be preserved. Old subscription
-# regress_sub1 should be enabled and old subscription regress_sub2 should be
-# disabled.
+# The subscription's running status and failover option should be preserved.
+# Old subscription regress_sub1 should have enabled and failover as true while
+# old subscription regress_sub2 should have enabled and failover as false.
 $result =
   $new_sub->safe_psql('postgres',
- "SELECT subname, subenabled FROM pg_subscription ORDER BY subname");
-is( $result, qq(regress_sub1|t
-regress_sub2|f),
+ "SELECT subname, subenabled, subfailover FROM pg_subscription ORDER
BY subname");
+is( $result, qq(regress_sub1|t|t
+regress_sub2|f|f),
  "check that the subscription's running status are preserved");

~

Calling those "old subscriptions" seems misleading. Aren't these the
new/upgraded subscriptions being checked here?

Should the comment be more like:

# The subscription's running status and failover option should be preserved.
# Upgraded regress_sub1 should still have enabled and failover as true.
# Upgraded regress_sub2 should still have enabled and failover as false.

======
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).