Horton

RE: Synchronizing slots from primary to standby

Zhijie Hou (Fujitsu) <houzj.fnst@fujitsu.com>

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From: "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>
To: Masahiko Sawada <sawada.mshk@gmail.com>
Cc: Amit Kapila <amit.kapila16@gmail.com>, shveta malik <shveta.malik@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>, Peter Smith <smithpb2250@gmail.com>, Bertrand Drouvot <bertranddrouvot.pg@gmail.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: 2024-03-01T07:21:18Z
Lists: pgsql-hackers 
On Friday, March 1, 2024 2:11 PM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
> 
> On Fri, Mar 1, 2024 at 12:42 PM Zhijie Hou (Fujitsu) <houzj.fnst@fujitsu.com>
> wrote:
> >
> > On Friday, March 1, 2024 10:17 AM Zhijie Hou (Fujitsu)
> <houzj.fnst@fujitsu.com> wrote:
> > >
> > >
> > > Attach the V102 patch set which addressed Amit and Shveta's comments.
> > > Thanks Shveta for helping addressing the comments off-list.
> >
> > The cfbot reported a compile warning, here is the new version patch
> > which fixed it, Also removed some outdate comments in this version.
> >
> 
> I've reviewed the v102-0001 patch. Here are some comments:

Thanks for the comments !

> 
> ---
> I got a compiler warning:
> 
> walsender.c:1829:6: warning: variable 'wait_event' is used uninitialized
> whenever '&&' condition is false [-Wsometimes-uninitialized]
>         if (!XLogRecPtrIsInvalid(RecentFlushPtr) &&
>             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> walsender.c:1871:7: note: uninitialized use occurs here
>                 if (wait_event ==
> WAIT_EVENT_WAL_SENDER_WAIT_FOR_WAL)
>                     ^~~~~~~~~~
> walsender.c:1829:6: note: remove the '&&' if its condition is always true
>         if (!XLogRecPtrIsInvalid(RecentFlushPtr) &&
>             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> walsender.c:1818:20: note: initialize the variable 'wait_event' to silence this
> warning
>         uint32          wait_event;
>                                   ^
>                                    = 0
> 1 warning generated.


Thanks for reporting, it was fixed in V102_2.

> 
> ---
> +void
> +assign_standby_slot_names(const char *newval, void *extra) {
> +        List      *standby_slots;
> +        MemoryContext oldcxt;
> +        char      *standby_slot_names_cpy = extra;
> +
> 
> Given that the newval and extra have the same data (standby_slot_names
> value), why do we not use newval instead? I think that if we use
> newval, we don't need to guc_strdup() in check_standby_slot_names(),
> we might need to do list_copy_deep() instead, though. It's not clear
> to me as there is no comment.

I think SplitIdentifierString will modify the passed in string, so we'd better
not pass the newval to it, otherwise the stored guc string(standby_slot_names)
will be changed. I can see we are doing similar thing in other GUC check/assign
function as well. (check_wal_consistency_checking/
assign_wal_consistency_checking, check_createrole_self_grant/
assign_createrole_self_grant ...).

> ---
> +        /*
> +         * Switch to the memory context under which GUC variables are
> allocated
> +         * (GUCMemoryContext).
> +         */
> +        oldcxt =
> MemoryContextSwitchTo(GetMemoryChunkContext(standby_slot_names_cpy
> ));
> +        standby_slot_names_list = list_copy(standby_slots);
> +        MemoryContextSwitchTo(oldcxt);
> 
> Why do we not explicitly switch to GUCMemoryContext?

I think it's because the GUCMemoryContext is not exposed.

Best Regards,
Hou zj

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).