Horton

Re: Synchronizing slots from primary to standby

Bertrand Drouvot <bertranddrouvot.pg@gmail.com>

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From: "Drouvot, Bertrand" <bertranddrouvot.pg@gmail.com>
To: shveta malik <shveta.malik@gmail.com>, Amit Kapila <amit.kapila16@gmail.com>
Cc: Peter Smith <smithpb2250@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: 2023-10-17T15:36:51Z
Lists: pgsql-hackers 
Hi,

On 10/13/23 10:35 AM, shveta malik wrote:
> On Thu, Oct 12, 2023 at 9:18 AM shveta malik <shveta.malik@gmail.com> wrote:
>>
> 
> PFA v24 patch set which has below changes:
> 
> 1) 'enable_failover' displayed in pg_replication_slots.
> 2) Support for 'enable_failover' in
> pg_create_logical_replication_slot(). It is an optional argument with
> default value false.
> 3) Addressed pending comments (1-30) from Peter in [1].
> 4) Fixed an issue in patch002 due to which even slots with
> enable_failover=false were getting synced.
> 
> The changes for 1 and 2 are in patch001 while 3 and 4 are in patch0002
> 
> Thanks Ajin, for working on 1 and 3.

Thanks for the hard work!

+   if (RecoveryInProgress())
+       wrconn = slotsync_remote_connect(NULL);

does produce at compilation time:

launcher.c:1916:40: warning: too many arguments in call to 'slotsync_remote_connect'
                 wrconn = slotsync_remote_connect(NULL);

Looking at 0001:

commit message:

"is added at the slot level which
     will be persistent information"

what about "which is persistent information" ?

Code:

+       True if this logical slot is enabled to be synced to the physical standbys
+       so that logical replication is not blocked after failover. Always false
+       for physical slots.

Not sure "not blocked" is the right wording. "can be resumed from the new primary" maybe?

+static void
+ProcessRepliesAndTimeOut(void)
+{
+       CHECK_FOR_INTERRUPTS();
+
+       /* Process any requests or signals received recently */
+       if (ConfigReloadPending)
+       {
+               ConfigReloadPending = false;
+               ProcessConfigFile(PGC_SIGHUP);
+               SyncRepInitConfig();
+               SlotSyncInitConfig();
+       }

Do we want to do this at each place ProcessRepliesAndTimeOut() is being
called? I mean before this change it was not done in ProcessPendingWrites().

+ * Wait for physical standby to confirm receiving give lsn.

typo? s/give/given/


diff --git a/src/test/recovery/t/050_verify_slot_order.pl b/src/test/recovery/t/050_verify_slot_order.pl
new file mode 100644
index 0000000000..25b3d5aac2
--- /dev/null
+++ b/src/test/recovery/t/050_verify_slot_order.pl
@@ -0,0 +1,145 @@
+
+# Copyright (c) 2023, PostgreSQL Global Development Group
+

Regarding the TAP tests, should we also add some testing related to enable_failover being set
in pg_create_logical_replication_slot() and pg_logical_slot_get_changes() behavior too?

Please note that current comments are coming while
"quickly" going through 0001.

I'm planning to have a closer look at 0001 and 0002 too.

Regards,

-- 
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com

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).