Horton

RE: Synchronizing slots from primary to standby

Hayato Kuroda (Fujitsu) <kuroda.hayato@fujitsu.com>

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From: "Hayato Kuroda (Fujitsu)" <kuroda.hayato@fujitsu.com>
To: 'shveta malik' <shveta.malik@gmail.com>
Cc: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>, Amit Kapila <amit.kapila16@gmail.com>, "Drouvot, Bertrand" <bertranddrouvot.pg@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>, Peter Smith <smithpb2250@gmail.com>
Date: 2023-10-03T13:42:15Z
Lists: pgsql-hackers

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Dear Shveta,

While investigating more, I found that the launcher crashes while executing the
script. Please see attached one.

In this script, the subscriber was also the publisher. Both subscriber and
subscriber2 referred the same replication slot, which was synchronized by slotsync
worker. I was quite not sure the synchronization should be occurred in this case,
but at lease core must not be dumped. The secondary server crashed.

primary ---> secondary
     |           |
subscriber    subscriber2

I checked the stack trace and found that the apply worker crashed.

```
(gdb) bt
#0  0x0000000000b310a9 in check_for_freed_segments (area=0x3a4ec68) at ../postgres/src/backend/utils/mmgr/dsa.c:2248
#1  0x0000000000b2e856 in dsa_get_address (area=0x3a4ec68, dp=16384) at ../postgres/src/backend/utils/mmgr/dsa.c:959
#2  0x00000000008a2bb5 in slotsync_remove_obsolete_dbs (remote_dbs=0x1fcea70)
    at ../postgres/src/backend/replication/logical/launcher.c:1615
#3  0x00000000008a318d in ApplyLauncherStartSlotSync (wait_time=0x7ffe15cd57a8, wrconn=0x1f82ec0)
    at ../postgres/src/backend/replication/logical/launcher.c:1799
#4  0x00000000008a3667 in ApplyLauncherMain (main_arg=0) at ../postgres/src/backend/replication/logical/launcher.c:1967
#5  0x0000000000863aef in StartBackgroundWorker () at ../postgres/src/backend/postmaster/bgworker.c:867
#6  0x000000000086e260 in do_start_bgworker (rw=0x1f6b4e0) at ../postgres/src/backend/postmaster/postmaster.c:5740
#7  0x000000000086e649 in maybe_start_bgworkers () at ../postgres/src/backend/postmaster/postmaster.c:5964
#8  0x000000000086953d in ServerLoop () at ../postgres/src/backend/postmaster/postmaster.c:1852
#9  0x0000000000868c42 in PostmasterMain (argc=3, argv=0x1f3e240) at ../postgres/src/backend/postmaster/postmaster.c:1465
#10 0x000000000075ad5f in main (argc=3, argv=0x1f3e240) at ../postgres/src/backend/main/main.c:198
```

Best Regards,
Hayato Kuroda
FUJITSU LIMITED

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).