Horton

Re: Synchronizing slots from primary to standby

Bertrand Drouvot <bertranddrouvot.pg@gmail.com>

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From: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
To: shveta malik <shveta.malik@gmail.com>
Cc: Amit Kapila <amit.kapila16@gmail.com>, Masahiko Sawada <sawada.mshk@gmail.com>, "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.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>
Date: 2024-02-22T11:05:19Z
Lists: pgsql-hackers 
Hi,

On Thu, Feb 22, 2024 at 04:01:34PM +0530, shveta malik wrote:
> On Thu, Feb 22, 2024 at 3:44 PM Bertrand Drouvot
> <bertranddrouvot.pg@gmail.com> wrote:
> >
> > Hi,
> >
> > Thanks!
> >
> > Some random comments about v92_001 (Sorry if it has already been discussed
> > up-thread):
> 
> Thanks for the feedback. The patch is pushed 15 minutes back.

Yeah, saw that after I send the comments ;-)

> I will
> prepare a top-up patch for your comments.

Thanks!

> > 4 ===
> >
> > +       if (wal_level < WAL_LEVEL_LOGICAL)
> > +       {
> > +               ereport(ERROR,
> > +                               errcode(ERRCODE_INVALID_PARAMETER_VALUE),
> > +                               errmsg("slot synchronization requires wal_level >= \"logical\""));
> > +               return false;
> > +       }
> >
> > I think the return is not needed here as it won't be reached due to the "ERROR".
> > Or should we use "elevel" instead of "ERROR"?
> 
> It was suggested to raise ERROR for wal_level validation, please see
> [1]. But yes, I will  remove the return value.

Yeah, thanks, ERROR makes sense here.

> > 5 ===
> >
> > +        * operate as a superuser. This is safe because the slot sync worker does
> > +        * not interact with user tables, eliminating the risk of executing
> > +        * arbitrary code within triggers.
> >
> > Right. I did not check but if we are using operators in our remote SPI calls
> > then it would be worth to ensure they are coming from the pg_catalog schema?
> > Using something like "OPERATOR(pg_catalog.=)" using "=" as an example.
> 
> Can you please elaborate this one, I am not sure if I understood it.

Suppose that in synchronize_slots() the query would be:

    const char *query = "SELECT slot_name, plugin, confirmed_flush_lsn,"
        " restart_lsn, catalog_xmin, two_phase, failover,"
        " database, conflict_reason"
        " FROM pg_catalog.pg_replication_slots"
        " WHERE failover and NOT temporary and 1 = 1";

Then my comment is to rewrite it to:

    const char *query = "SELECT slot_name, plugin, confirmed_flush_lsn,"
        " restart_lsn, catalog_xmin, two_phase, failover,"
        " database, conflict_reason"
        " FROM pg_catalog.pg_replication_slots"
        " WHERE failover and NOT temporary and 1 OPERATOR(pg_catalog.=) 1";

to ensure the operator "=" is coming from the pg_catalog schema.

Regards,

-- 
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com

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).