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: Peter Smith <smithpb2250@gmail.com>
Cc: shveta malik <shveta.malik@gmail.com>, "Drouvot, Bertrand" <bertranddrouvot.pg@gmail.com>, Nisha Moond <nisha.moond412@gmail.com>, "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.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: 2023-12-14T11:10:34Z
Lists: pgsql-hackers 
On Thu, Dec 14, 2023 at 7:00 AM Peter Smith <smithpb2250@gmail.com> wrote:
>
> Hi, here are a few more review comments for the patch v47-0002
>
> (plus my review comments of v45-0002 [1] are yet to be addressed)
>
> ======
> 1. General
>
> For consistency and readability, try to use variables of the same
> names whenever they have the same purpose, even when they declared are
> in different functions. A few like this were already mentioned in the
> previous review but there are more I keep noticing.
>
> For example,
> 'slotnameChanged' in function, VERSUS 'primary_slot_changed' in the caller.
>
>
> ======
> src/backend/replication/logical/slotsync.c
>
> 2.
> +/*
> + *
> + * Validates the primary server info.
> + *
> + * Using the specified primary server connection, it verifies whether
> the master
> + * is a standby itself and returns true in that case to convey the caller that
> + * we are on the cascading standby.
> + * But if master is the primary server, it goes ahead and validates
> + * primary_slot_name. It emits error if the physical slot in primary_slot_name
> + * does not exist on the primary server.
> + */
> +static bool
> +validate_primary_info(WalReceiverConn *wrconn)
>
> 2b.
> IMO it is too tricky to have a function called "validate_xxx", when
> actually you gave that return value some special unintuitive meaning
> other than just validation. IMO it is always better for the returned
> value to properly match the function name so the expectations are very
> obvious. So, In this case, I think a better function signature would
> be like this:
>
> SUGGESTION
>
> static void
> validate_primary_info(WalReceiverConn *wrconn, bool *master_is_standby)
>
> or
>
> static void
> validate_primary_info(WalReceiverConn *wrconn, bool *am_cascading_standby)
>

The terminology master_is_standby is a bit indirect for this usage, so
I would prefer the second one. Shall we name this function as
check_primary_info()? Additionally, can we rewrite the following
comment: "Using the specified primary server connection, check whether
we are cascading standby. It also validates primary_slot_info for
non-cascading-standbys.".

-- 
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).