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: "Drouvot, Bertrand" <bertranddrouvot.pg@gmail.com>, Nisha Moond <nisha.moond412@gmail.com>, "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.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>, Ajin Cherian <itsajin@gmail.com>, Alvaro Herrera <alvherre@alvh.no-ip.org>
Date: 2023-12-07T11:36:50Z
Lists: pgsql-hackers

Attachments

On Wed, Dec 6, 2023 at 4:53 PM shveta malik <shveta.malik@gmail.com> wrote:
>
> v43-001:
> 1) Support of  'failover' dump in pg_dump. It was missing earlier.
>

Review v43-0001
================
1.
+ * However, we do not enable failover for slots created by the table sync
+ * worker. This is because the table sync slot might not be fully synced on the
+ * standby.

The reason for not enabling failover for table sync slots is not
clearly mentioned.

2.
During syncing, the local restart_lsn and/or local catalog_xmin of
+ * the newly created slot on the standby are typically ahead of those on the
+ * primary. Therefore, the standby needs to wait for the primary server's
+ * restart_lsn and catalog_xmin to catch up, which takes time.

I think this part of the comment should be moved to 0002 patch. We can
probably describe a bit more about why slot on standby will be ahead
and about waiting time.

3.
validate_standby_slots()
{
...
+ slot = SearchNamedReplicationSlot(name, true);
+
+ if (!slot)
+ goto ret_standby_slot_names_ng;
+
+ if (!SlotIsPhysical(slot))
+ {
+ GUC_check_errdetail("\"%s\" is not a physical replication slot",
+ name);
+ goto ret_standby_slot_names_ng;
+ }

Why the first check (slot not found) doesn't have errdetail? The
goto's in this function look a bit odd, can we try to avoid those?

4.
+ /* Verify syntax and parse string into list of identifiers */
+ if (!SplitIdentifierString(rawname, ',', &elemlist))
+ {
+ /* syntax error in name list */
+ GUC_check_errdetail("List syntax is invalid.");
...
...
+ if (!SplitIdentifierString(standby_slot_names_cpy, ',', &standby_slots))
+ {
+ /* This should not happen if GUC checked check_standby_slot_names. */
+ elog(ERROR, "invalid list syntax");

Both are checking the same string but giving different error messages.
I think the error message should be the same in both cases. The first
one seems better.

5. In WalSndFilterStandbySlots(), the comments around else if checks
should move inside the checks. It is hard to read the code in the
current format. I have tried to change the same in the attached.

Apart from the above, I have changed the comments and made some minor
cosmetic changes in the attached. Kindly include in next version if
you are fine with it.

-- 
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).