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: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Cc: "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>, Masahiko Sawada <sawada.mshk@gmail.com>, shveta malik <shveta.malik@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>
Date: 2024-02-12T10:49:33Z
Lists: pgsql-hackers 
On Mon, Feb 12, 2024 at 3:33 PM Bertrand Drouvot
<bertranddrouvot.pg@gmail.com> wrote:
>
> A few random comments:
>
>
> 003 ===
>
> +          If, after executing the function,
> +          <link linkend="guc-hot-standby-feedback">
> +          <varname>hot_standby_feedback</varname></link> is disabled on
> +          the standby or the physical slot configured in
> +          <link linkend="guc-primary-slot-name">
> +          <varname>primary_slot_name</varname></link> is
> +          removed,
>
> I think another option that could lead to slot invalidation is if primary_slot_name
> is NULL or miss-configured.
>

If the primary_slot_name is NULL then the function will error out. So,
not sure, if we need to say anything explicitly here.

> Indeed hot_standby_feedback would be working
> (for the catalog_xmin) but only as long as the standby is up and running.
>
...
>
> 005 ===
>
> +     To resume logical replication after failover from the synced logical
> +     slots, the subscription's 'conninfo' must be altered
>
> Only in a pub/sub context but not for other ways of using the logical replication
> slot(s).
>

Right, but what additional information do you want here? I thought we
were speaking about the in-build logical replication here so this is
okay.

>
> 008 ===
>
> +                       ereport(LOG,
> +                                       errmsg("dropped replication slot \"%s\" of dbid %d",
> +                                                  NameStr(local_slot->data.name),
> +                                                  local_slot->data.database));
>
> We emit a message when an "invalidated" slot is dropped but not when we create
> a slot. Shouldn't we emit a message when we create a synced slot on the standby?
>
> I think that could be confusing to see "a drop" message not followed by "a create"
> one when it's expected (slot valid on the primary for example).
>

Isn't the below message for sync-ready slot sufficient? Otherwise, in
most cases, we will LOG multiple similar messages.

+ ereport(LOG,
+ errmsg("newly created slot \"%s\" is sync-ready now",
+    remote_slot->name));

-- 
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).