Horton

Re: Synchronizing slots from primary to standby

Amit Kapila <amit.kapila16@gmail.com>

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From: Amit Kapila <amit.kapila16@gmail.com>
To: shveta malik <shveta.malik@gmail.com>
Cc: "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>, Masahiko Sawada <sawada.mshk@gmail.com>, Peter Smith <smithpb2250@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>, Bertrand Drouvot <bertranddrouvot.pg@gmail.com>, shveta malik <shvetamalik@gmail.com>
Date: 2024-02-19T12:01:53Z
Lists: pgsql-hackers

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On Mon, Feb 19, 2024 at 9:46 AM shveta malik <shveta.malik@gmail.com> wrote:
>
> Okay I see. Thanks for pointing it out. Here are the patches
> addressing your comments. Changes are in patch001, rest are rebased.
>

Few comments on 0001
====================
1. I think it is better to error out when the valid GUC or option is
not set in ensure_valid_slotsync_params() and
ensure_valid_remote_info() instead of waiting. And we shouldn't start
the worker in the first place if not all required GUCs are set. This
will additionally simplify the code a bit.

2.
+typedef struct SlotSyncWorkerCtxStruct
 {
- /* prevents concurrent slot syncs to avoid slot overwrites */
+ pid_t pid;
+ bool stopSignaled;
  bool syncing;
+ time_t last_start_time;
  slock_t mutex;
-} SlotSyncCtxStruct;
+} SlotSyncWorkerCtxStruct;

I think we don't need to change the name of this struct as this can be
used both by the worker and the backend. We can probably add the
comment to indicate that all the fields except 'syncing' are used by
slotsync worker.

3. Similar to above, function names like SlotSyncShmemInit() shouldn't
be changed to SlotSyncWorkerShmemInit().

4.
+ReplSlotSyncWorkerMain(int argc, char *argv[])
{
...
+ on_shmem_exit(slotsync_worker_onexit, (Datum) 0);
...
+ before_shmem_exit(slotsync_failure_callback, PointerGetDatum(wrconn));
...
}

Do we need two separate callbacks? Can't we have just one (say
slotsync_failure_callback) that cleans additional things in case of
slotsync worker? And, if we need both those callbacks then please add
some comments for both and why one is before_shmem_exit() and the
other is on_shmem_exit().

In addition to the above, I have made a few changes in the comments
and code (cosmetic code changes). Please include those in the next
version if you find them okay. You need to rename .txt file to remove
.txt and apply atop v90-0001*.

-- 
With Regards,
Amit Kapila.

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).