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: "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>
Cc: Amit Kapila <amit.kapila16@gmail.com>, Bertrand Drouvot <bertranddrouvot.pg@gmail.com>, Masahiko Sawada <sawada.mshk@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>, shveta malik <shveta.malik@gmail.com>
Date: 2024-02-29T11:35:50Z
Lists: pgsql-hackers 
On Thu, Feb 29, 2024 at 7:04 AM Zhijie Hou (Fujitsu)
<houzj.fnst@fujitsu.com> wrote:
>
> Here is the v101 patch set which addressed above comments.
>

Thanks for the patch. Few comments:

1)  Shall we mention in doc that shutdown will wait for standbys in
standby_slot_names to confirm receiving WAL:

Suggestion for logicaldecoding.sgml:

When <varname>standby_slot_names</varname> is utilized, the primary
server will not completely shut down until the corresponding standbys,
associated with the physical replication slots specified in
<varname>standby_slot_names</varname>, have confirmed receiving the
WAL up to the latest flushed position on the primary server.

slot.c
2)
/*
 * If a logical slot name is provided in standby_slot_names, report
 * a message and skip it. Although logical slots are disallowed in
 * the GUC check_hook(validate_standby_slots), it is still
 * possible for a user to drop an existing physical slot and
 * recreate a logical slot with the same name.
 */

This is not completely true, we can still specify a logical slot
during instance start and it will accept it.

Suggestion:
/*
 * If a logical slot name is provided in standby_slot_names, report
 * a message and skip it. It is possible for user to specify a
 * logical slot name in standby_slot_names just before the server
 * startup. The GUC check_hook(validate_standby_slots) can not
 * validate such a slot during startup as the ReplicationSlotCtl
 * shared memory is not initialized by that time. It is also
 * possible for user to drop an existing physical slot and
 * recreate a logical slot with the same name.
 */

3. Wait for physical standby to confirm receiving the given lsn

standby -->standbys


4.
In StandbyConfirmedFlush(), is it better to have below errdetail in
all problematic cases:
Logical replication is waiting on the standby associated with \"%s\

We have it only for inactive pid case but we are waiting in all cases.


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).