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: shveta malik <shveta.malik@gmail.com>
Cc: Amit Kapila <amit.kapila16@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>, Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Date: 2024-02-18T14:09:54Z
Lists: pgsql-hackers 
On Friday, February 16, 2024 6:41 PM shveta malik <shveta.malik@gmail.com> wrote:
> 
> On Thu, Feb 15, 2024 at 10:48 PM Bertrand Drouvot
> <bertranddrouvot.pg@gmail.com> wrote:
> >
> > Looking at v88_0001, random comments:
> 
> Thanks for the feedback.
> 
> >
> > 1 ===
> >
> > Commit message "Be enabling slot synchronization"
> >
> > Typo? s:Be/By
> 
> Modified.
> 
> > 2 ===
> >
> > +        It enables a physical standby to synchronize logical failover slots
> > +        from the primary server so that logical subscribers are not blocked
> > +        after failover.
> >
> > Not sure "not blocked" is the right wording.
> > "can be resumed from the new primary" maybe? (was discussed in [1])
> 
> Modified.
> 
> > 3 ===
> >
> > +#define SlotSyncWorkerAllowed()        \
> > +       (sync_replication_slots && pmState == PM_HOT_STANDBY && \
> > +        SlotSyncWorkerCanRestart())
> >
> > Maybe add a comment above the macro explaining the logic?
> 
> Done.
> 
> > 4 ===
> >
> > +#include "replication/walreceiver.h"
> >  #include "replication/slotsync.h"
> >
> > should be reverse order?
> 
> Removed walreceiver.h inclusion as it was not needed.
> 
> > 5 ===
> >
> > +       if (SlotSyncWorker->syncing)
> >         {
> > -               SpinLockRelease(&SlotSyncCtx->mutex);
> > +               SpinLockRelease(&SlotSyncWorker->mutex);
> >                 ereport(ERROR,
> >
> errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
> >                                 errmsg("cannot synchronize replication
> slots concurrently"));
> >         }
> >
> > worth to add a test in 040_standby_failover_slots_sync.pl for it?
> 
> It will be very difficult to stabilize this test as we have to make sure that the
> concurrent users (SQL function(s) and/or worker(s)) are in that target function at
> the same time to hit it.
> 
> >
> > 6 ===
> >
> > +static void
> > +slotsync_reread_config(bool restart)
> > +{
> >
> > worth to add test(s) in 040_standby_failover_slots_sync.pl for it?
> 
> Added test.
> 
> Please find v89  patch set. The other changes are:

Thanks for the patch. Here are few comments:

1.

+static char *
+get_dbname_from_conninfo(const char *conninfo)
+{
+	static char *dbname;
+
+	if (dbname)
+		return dbname;
+	else
+		dbname = walrcv_get_dbname_from_conninfo(conninfo);
+
+	return dbname;
+}


I think it's not necessary to have a static variable here, because the guc
check doesn't seem performance sensitive. Additionaly, it does not work well
with slotsync SQL functions, because the dbname will be allocated in temp
memory context when reaching here via SQL function, so it's not safe to access
this static variable in next function call.

2.

+static bool
+validate_remote_info(WalReceiverConn *wrconn, int elevel)
...
+
+	return (!remote_in_recovery && primary_slot_valid);

The primary_slot_valid could be uninitialized in this function.

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).