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: Amit Kapila <amit.kapila16@gmail.com>
Cc: "Drouvot, Bertrand" <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>, Ajin Cherian <itsajin@gmail.com>, Alvaro Herrera <alvherre@alvh.no-ip.org>, shveta malik <shveta.malik@gmail.com>
Date: 2023-09-11T02:56:21Z
Lists: pgsql-hackers

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On Fri, Sep 8, 2023 at 1:54 PM shveta malik <shveta.malik@gmail.com> wrote:
>
> On Thu, Sep 7, 2023 at 8:29 AM shveta malik <shveta.malik@gmail.com> wrote:
> >
> > On Fri, Aug 25, 2023 at 2:15 PM Alvaro Herrera <alvherre@alvh.no-ip.org> wrote:
> > >
> > > Wait a minute ...
> > >
> > > From bac0fbef8b203c530e5117b0b7cfee13cfab78b9 Mon Sep 17 00:00:00 2001
> > > From: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>
> > > Date: Sat, 22 Jul 2023 10:17:48 +0000
> > > Subject: [PATCH v13 1/2] Allow logical walsenders to wait for physical
> > >  standbys
> > >
> > > @@ -2498,6 +2500,13 @@ ReorderBufferProcessTXN(ReorderBuffer *rb, ReorderBufferTXN *txn,
> > >                 }
> > >                 else
> > >                 {
> > > +                       /*
> > > +                        * Before we send out the last set of changes to logical decoding
> > > +                        * output plugin, wait for specified streaming replication standby
> > > +                        * servers (if any) to confirm receipt of WAL upto commit_lsn.
> > > +                        */
> > > +                       WaitForStandbyLSN(commit_lsn);
> > >
> > > OK, so we call this new function frequently enough -- once per
> > > transaction, if I read this correctly?  So ...
> > >
> > > +void
> > > +WaitForStandbyLSN(XLogRecPtr wait_for_lsn)
> > > +{
> > >  ...
> > >
> > > +       /* "*" means all logical walsenders should wait for physical standbys. */
> > > +       if (strcmp(synchronize_slot_names, "*") != 0)
> > > +       {
> > > +               bool    shouldwait = false;
> > > +
> > > +               rawname = pstrdup(synchronize_slot_names);
> > > +               SplitIdentifierString(rawname, ',', &elemlist);
> > > +
> > > +               foreach (l, elemlist)
> > > +               {
> > > +                       char *name = lfirst(l);
> > > +                       if (strcmp(name, NameStr(MyReplicationSlot->data.name)) == 0)
> > > +                       {
> > > +                               shouldwait = true;
> > > +                               break;
> > > +                       }
> > > +               }
> > > +
> > > +               pfree(rawname);
> > > +               rawname = NULL;
> > > +               list_free(elemlist);
> > > +               elemlist = NIL;
> > > +
> > > +               if (!shouldwait)
> > > +                       return;
> > > +       }
> > > +
> > > +       rawname = pstrdup(standby_slot_names);
> > > +       SplitIdentifierString(rawname, ',', &elemlist);
> > >
> > > ... do we really want to be doing the GUC string parsing every time
> > > through it?  This sounds like it could be a bottleneck, or at least slow
> > > things down.  Maybe we should think about caching this somehow.
> > >
> >
> > Yes, these parsed lists are now cached. Please see v15
> > (https://www.postgresql.org/message-id/CAJpy0uAuzbzvcjpnzFTiWuDBctnH-SDZC6AZabPX65x9GWBrjQ%40mail.gmail.com)
> >
> > thanks
> > Shveta
>
> Patches (v15) were no longer applying to HEAD, rebased those and
> addressed below along-with:
>
> 1) Fixed an issue in slots-invalidation code-path on standby. Thanks
> Ajin for testing the patch and finding the issue.
> 2) Ensure that WAL is replayed on standby before moving the slot's
> position to the target location received from the primary.
> 3) Some code restructuring in slotsync.c
>
> thanks
> Shveta

There were cfbot failures on v16 patches:
--presence of 051_slot_sync.pl in meson.build even though the file is removed.
--usage of uint in launcher.c

Fixed above and attached v16_2_0001/0002 patches again.

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).