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>, "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>, Bertrand Drouvot <bertranddrouvot.pg@gmail.com>, Ajin Cherian <itsajin@gmail.com>, Masahiko Sawada <sawada.mshk@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: 2024-02-05T03:36:45Z
Lists: pgsql-hackers 
On Fri, Feb 2, 2024 at 11:18 PM shveta malik <shveta.malik@gmail.com> wrote:
>
> On Fri, Feb 2, 2024 at 12:25 PM Peter Smith <smithpb2250@gmail.com> wrote:
> >
> > Here are some review comments for v750002.
>
> Thanks for the feedback Peter. Addressed all in v76 except one.
>
> > (this is a WIP but this is what I found so far...)
>
> > I wonder if it is better to log all the problems in one go instead of
> > making users stumble onto them one at a time after fixing one and then
> > hitting the next problem. e.g. just set some variable "all_ok =
> > false;" each time instead of all the "return false;"
> >
> > Then at the end of the function just "return all_ok;"
>
> If we do this way, then we need to find a way to combine the msgs as
> well, otherwise the same msg will be repeated multiple times. For the
> concerned functionality (which needs one time config effort by user),
> I feel the existing way looks okay. We may consider optimizing it if
> we get more comments here.
>

I don't think combining messages is necessary;   I considered these
all as different (not the same msg repeated multiple times) since they
all have different errhints.

I felt a user would only know to make a configuration correction when
they are informed something is wrong, so my review point was we could
tell them all the wrong things up-front so then those can all be fixed
with a "one time config effort by user".

Otherwise, if multiple settings (e.g. from the list below) have wrong
values, I imagined the user will fix the first reported one, then the
next bad config will be reported, then the user will fix that one,
then the next bad config will be reported, then the user will fix that
one, and so on. It just seemed potentially/unnecessarilly painful.

- errhint("\"%s\" must be defined.", "primary_slot_name"));
- errhint("\"%s\" must be enabled.", "hot_standby_feedback"));
- errhint("\"wal_level\" must be >= logical."));
- errhint("\"%s\" must be defined.", "primary_conninfo"));
- errhint("'dbname' must be specified in \"%s\".", "primary_conninfo"));

~

Anyway, I just wanted to explain my review comment some more because
maybe my reason wasn't clear the first time. Whatever your decision
is, it is fine by me.

======
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).