Horton

Re: Synchronizing slots from primary to standby

shveta malik <shveta.malik@gmail.com>

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From: shveta malik <shveta.malik@gmail.com>
To: "Drouvot, Bertrand" <bertranddrouvot.pg@gmail.com>
Cc: Amit Kapila <amit.kapila16@gmail.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>, shveta malik <shveta.malik@gmail.com>
Date: 2023-11-08T11:50:56Z
Lists: pgsql-hackers 
On Wed, Nov 8, 2023 at 3:19 PM Drouvot, Bertrand
<bertranddrouvot.pg@gmail.com> wrote:
>
> Hi,
>
> On 11/8/23 9:57 AM, Amit Kapila wrote:
> > On Wed, Nov 8, 2023 at 12:32 PM Drouvot, Bertrand
> > <bertranddrouvot.pg@gmail.com> wrote:
> >>
> >> Hi,
> >>
> >> On 11/8/23 4:50 AM, Amit Kapila wrote:
> >>
> >>> I think if we want to follow
> >>> this approach then we need to also monitor these slots for any change
> >>> in the consecutive cycles and if we are able to sync them then
> >>> accordingly we enable them to use after failover.
> >>
> >> What about to add a new field in ReplicationSlotPersistentData
> >> indicating that we are waiting for "sync" and drop such slots during promotion and
> >> /or if not in recovery?
> >>
> >
> > This patch is already adding 'synced' flag in
> > ReplicationSlotPersistentData to distinguish synced slots so that we
> > can disallow decoding on then in standby and disallow to drop those. I
> > suggest we change that field to have multiple states where one of the
> > states would indicate that the initial sync of the slot is done.
> >
>
> Yeah, agree.
>

I am working on this implementation. This sync-state is even needed
for cascading standbys to know when to start syncing the slots from
the first standby. It should start syncing only after the first
standby has finished initialization of it (i.e. wait for primary is
over) and not before that.

Unrelated to above, if there is a user slot on standby with the same
name which the slot-sync worker is trying to create, then shall it
emit a warning and skip the sync of that slot or shall it throw an
error?

thanks
Shveta

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).