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>, Ajin Cherian <itsajin@gmail.com>
Cc: "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>, Amit Kapila <amit.kapila16@gmail.com>, 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>, Alvaro Herrera <alvherre@alvh.no-ip.org>
Date: 2023-12-01T10:57:04Z
Lists: pgsql-hackers 
Hi,

On 12/1/23 4:19 AM, shveta malik wrote:
> On Thu, Nov 30, 2023 at 5:37 PM Ajin Cherian <itsajin@gmail.com> wrote:
>>
>>
>> 1. In my opinion, the second message "aborting the wait...moving to
>> the next slot" does not hold much value. There might not even be a
>> "next slot", there might be just one slot. I think the first LOG is
>> enough to indicate that the sync-slot is waiting as it repeats this
>> log till the slot catches up. I know these messages hold great value
>> for debugging but in production,  "waiting..", "aborting the wait.."
>> might not be as helpful, maybe change it to debug?
>>
>> 2023-11-30 05:13:49.811 EST [6115] LOG:  waiting for remote slot
>> "sub1" LSN (0/3047A90) and catalog xmin (745) to pass local slot LSN
>> (0/3047AC8) and catalog xmin (745)
>> 2023-11-30 05:13:57.909 EST [6115] LOG:  aborting the wait for remote
>> slot "sub1" and moving to the next slot, will attempt creating it
>> again
>> 2023-11-30 05:14:07.921 EST [6115] LOG:  waiting for remote slot
>> "sub1" LSN (0/3047A90) and catalog xmin (745) to pass local slot LSN
>> (0/3047AC8) and catalog xmin (745)
>>
> 
> Sure, the message can be trimmed down. But I am not very sure if we
> should convert it to DEBUG. It might be useful to know what exactly is
> happening with this slot through the log file.Curious to know what
> others think here?
> 

I think LOG is fine for the "waiting" one but I'd be tempted to put part of the
message in errdetail().

I think we could get rid of the "aborting" message (or move it to DEBUG). I mean
if one does not see the "newly locally created slot" message then I think it's
enough to guess the wait has been aborted or that it is still waiting.

But that's probably just a matter of taste.

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).