Horton

Re: Synchronizing slots from primary to standby

Peter Smith <smithpb2250@gmail.com>

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From: Peter Smith <smithpb2250@gmail.com>
To: shveta malik <shveta.malik@gmail.com>
Cc: Amit Kapila <amit.kapila16@gmail.com>, "Drouvot, Bertrand" <bertranddrouvot.pg@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: 2023-10-24T07:35:42Z
Lists: pgsql-hackers 
Here are some review comments for patch v25-0002

(additional to v25-0002 review comments [1])

======
src/backend/catalog/system_views.sql

1.
@@ -1003,7 +1003,8 @@ CREATE VIEW pg_replication_slots AS
             L.safe_wal_size,
             L.two_phase,
             L.conflicting,
-            L.failover
+            L.failover,
+            L.synced_slot
     FROM pg_get_replication_slots() AS L
             LEFT JOIN pg_database D ON (L.datoid = D.oid);

AFAICT the patch is missing PG DOCS descriptions for these new view attributes.

======
src/backend/replication/logical/launcher.c

2. slotsync_remove_obsolete_dbs

+
+ /*
+ * TODO: Take care of of removal of old 'synced' slots for the dbs which
+ * are no longer eligible for slot-sync.
+ */

typo: "of of"

~~~

3.
+ /*
+ * Make sure that concerned WAL is received before syncing slot to target
+ * lsn received from the primary.
+ *
+ * This check should never pass as on the primary, we have waited for
+ * standby's confirmation before updating the logical slot. But to take
+ * care of any bug in that flow, we should retain this check.
+ */
+ if (remote_slot->confirmed_lsn > WalRcv->latestWalEnd)
+ {
+ ereport(LOG,
+ errmsg_internal("skipping sync of slot \"%s\" as the received slot-sync "
+ "lsn %X/%X is ahead of the standby position %X/%X",
+ remote_slot->name,
+ LSN_FORMAT_ARGS(remote_slot->confirmed_lsn),
+ LSN_FORMAT_ARGS(WalRcv->latestWalEnd)));
+ return;
+ }

Would elog be better here than using ereport(LOG, errmsg_internal...);
IIUC it does the same thing?

======
[1] https://www.postgresql.org/message-id/CAHut%2BPspseC03Fhsi%3DOqOtksagspE%2B0MVOhrhhUb64cc_4SE1w%40mail.gmail.com

Kind Regards,
Peter Smith.
Fujitsu Australia

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).