Horton

Re: Synchronizing slots from primary to standby

Bertrand Drouvot <bertranddrouvot.pg@gmail.com>

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From: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
To: Peter Smith <smithpb2250@gmail.com>
Cc: Amit Kapila <amit.kapila16@gmail.com>, shveta malik <shveta.malik@gmail.com>, "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>, Masahiko Sawada <sawada.mshk@gmail.com>, Ajin Cherian <itsajin@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: 2024-02-29T07:09:03Z
Lists: pgsql-hackers 
Hi,

On Thu, Feb 29, 2024 at 10:43:07AM +1100, Peter Smith wrote:
> - if (logical)
> + /*
> + * Set always-secure search path for the cases where the connection is
> + * used to run SQL queries, so malicious users can't get control.
> + */
> + if (logical || !replication)
>   {
>   PGresult   *res;
> 
> I found this condition a bit confusing. According to the
> libpqrcv_connect function comment:
> 
>  * This function can be used for both replication and regular connections.
>  * If it is a replication connection, it could be either logical or physical
>  * based on input argument 'logical'.
> 
> IIUC that comment is saying the 'replication' flag is like the main
> categorization and the 'logical' flag is like a subcategory (for when
> 'replication' is true). Therefore, won't the modified check be better
> to be written the other way around? This will also be consistent with
> the way the Assert was written.
> 
> SUGGESTION
> if (!replication || logical)
> {
>   ...

Thanks for the review!

Yeah, that makes sense from a categorization point of view.

Out of curiosity, I checked which condition returns true most of the time by:

Looking at the walrcv_connect calls:

logical: 6 times
!replication: 2 times (only for sync slot related stuff)

Looking at a check-world coverage:

logical: 1006 times
!replication: 16 times

So according to the above, using what has been proposed initially:

"
if (logical || !replication)
"

provides the benefit to avoid the second check on !replication most of the time
(at least during check-world).

Of course it also all depends if the slot sync feature (the only one that makes
use of !replication) is used or not.

Based on the above, I did prefer the original proposal but I think we can keep
what has been pushed (Peter's proposal). 

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).