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Re: Adding REPACK [concurrently]

Srinath Reddy Sadipiralla <srinath2133@gmail.com>

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From: Srinath Reddy Sadipiralla <srinath2133@gmail.com>
To: Antonin Houska <ah@cybertec.at>
Cc: Alvaro Herrera <alvherre@alvh.no-ip.org>, Matthias van de Meent <boekewurm+postgres@gmail.com>, Mihail Nikalayeu <mihailnikalayeu@gmail.com>, Pg Hackers <pgsql-hackers@lists.postgresql.org>, Robert Treat <rob@xzilla.net>
Date: 2026-03-18T19:12:19Z
Lists: pgsql-hackers

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Hello,

While i was doing concurrency test onn V41 patches ,i found this crash
because of the assert failure,

TRAP: failed Assert("RelationGetRelid(relation) == ((RepackDecodingState *)
ctx->output_writer_private)->relid"), File: "pgoutput_repack.c", Line: 97,
PID: 397007
postgres: REPACK decoding worker for relation "stress_victim"
(ExceptionalCondition+0x98)[0xaaaad9361698]
/home/srinath/Desktop/pgbuild/lib/postgresql/pgoutput_repack.so(+0xfe8)[0xffff90e00fe8]
postgres: REPACK decoding worker for relation "stress_victim"
(+0x679e14)[0xaaaad9049e14]
postgres: REPACK decoding worker for relation "stress_victim"
(+0x689cd0)[0xaaaad9059cd0]
postgres: REPACK decoding worker for relation "stress_victim"
(+0x68a65c)[0xaaaad905a65c]
postgres: REPACK decoding worker for relation "stress_victim"
(+0x68b2f0)[0xaaaad905b2f0]
postgres: REPACK decoding worker for relation "stress_victim"
(ReorderBufferCommit+0x74)[0xaaaad905b374]
postgres: REPACK decoding worker for relation "stress_victim"
(+0x671ec4)[0xaaaad9041ec4]
postgres: REPACK decoding worker for relation "stress_victim"
(xact_decode+0x1a0)[0xaaaad9040edc]
postgres: REPACK decoding worker for relation "stress_victim"
(LogicalDecodingProcessRecord+0xd4)[0xaaaad9040a80]
postgres: REPACK decoding worker for relation "stress_victim"
(+0x33f558)[0xaaaad8d0f558]
postgres: REPACK decoding worker for relation "stress_victim"
(+0x341ccc)[0xaaaad8d11ccc]
postgres: REPACK decoding worker for relation "stress_victim"
(RepackWorkerMain+0x1ac)[0xaaaad8d11bd4]
postgres: REPACK decoding worker for relation "stress_victim"
(BackgroundWorkerMain+0x2b0)[0xaaaad900d21c]
postgres: REPACK decoding worker for relation "stress_victim"
(postmaster_child_launch+0x1f0)[0xaaaad9012070]
postgres: REPACK decoding worker for relation "stress_victim"
(+0x64b974)[0xaaaad901b974]
postgres: REPACK decoding worker for relation "stress_victim"
(+0x64bc64)[0xaaaad901bc64]
postgres: REPACK decoding worker for relation "stress_victim"
(+0x64a3e4)[0xaaaad901a3e4]
postgres: REPACK decoding worker for relation "stress_victim"
(+0x647648)[0xaaaad9017648]
postgres: REPACK decoding worker for relation "stress_victim"
(PostmasterMain+0x160c)[0xaaaad9016d98]
postgres: REPACK decoding worker for relation "stress_victim"
(main+0x3dc)[0xaaaad8ea7a38]
/lib/aarch64-linux-gnu/libc.so.6(+0x284c4)[0xffff9c5c84c4]
/lib/aarch64-linux-gnu/libc.so.6(__libc_start_main+0x98)[0xffff9c5c8598]
postgres: REPACK decoding worker for relation "stress_victim"
(_start+0x30)[0xaaaad8abc970]
2026-03-16 19:40:21.622 IST [393820] LOG:  background worker "REPACK
decoding worker" (PID 397007) was terminated by signal 6: Aborted
2026-03-16 19:40:21.622 IST [393820] LOG:  terminating any other active
server processes
2026-03-16 19:40:21.632 IST [397036] FATAL:  the database system is in
recovery mode

This crash happens if we run REPACK (concurrently) on a table while a heavy
pgbench workload is concurrently executing multi-table(setup.sql)
transactions(dual_chaos.sql).
It triggers after a few back to back REPACK (concurrently) runs.

i think i found the cause for this crash , because there were some changes
which
slipped under the nose of the change_useless_for_repack filter , which led
some
changes which are not related to the relation which we are currently doing
REPACK (concurrently)
got decoded and added into the reorderbuffer queue, the reason for this
is repacked_rel_locator.relNumber
is by default set to InvalidOid, this is actually set to the target
relation during setup_logical_decoding
but this done after DecodingContextFindStartpoint, in
DecodingContextFindStartpoint changes are not
filtered even if its not related to the target relation , because
rm_decode->change_useless_for_repack->am_decoding_for_repack
where repacked_rel_locator.relNumber is still InvalidOid, which makes it
skip the filtering even its not the target relation,
this makes it to be added to reorder buffer queue, so during the processing
of reorder buffer plugin_change is called
where assert fails, i have attached a diff patch to solve this.

thoughts?

-- 
Thanks,
Srinath Reddy Sadipiralla
EDB: https://www.enterprisedb.com/

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Allow old WAL recycling during REPACK CONCURRENTLY

  2. Advance restart_lsn more eagerly in LogicalConfirmReceivedLocation

  3. Remove unnecessary signal handler change

  4. Improve REPACK (CONCURRENTLY) error messages some more

  5. Revert "Allow logical replication snapshots to be database-specific"

  6. Move REPACK (CONCURRENTLY) test out of stock regression tests

  7. REPACK: do not require REPLICATION or LOGIN

  8. Add missing initialization

  9. Simplify declaration of memcpy target

  10. Reserve replication slots specifically for REPACK

  11. doc: Add an example of REPACK (CONCURRENTLY)

  12. Allow logical replication snapshots to be database-specific

  13. Avoid different-size pointer-to-integer cast

  14. Fix valgrind failure

  15. Add CONCURRENTLY option to REPACK

  16. Rename cluster.c to repack.c (and corresponding .h)

  17. Allow index_create to suppress index_build progress reporting

  18. Make index_concurrently_create_copy more general

  19. Document the 'command' column of pg_stat_progress_repack

  20. Introduce the REPACK command

  21. Toggle logical decoding dynamically based on logical slot presence.

  22. Split vacuumdb to create vacuuming.c/h

  23. Remove ReorderBufferTupleBuf structure.

  24. Revert changes to CONCURRENTLY that "sped up" Xmin advance

  25. VACUUM: ignore indexing operations with CONCURRENTLY