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RE: Perform streaming logical transactions by background workers and parallel apply

Zhijie Hou (Fujitsu) <houzj.fnst@fujitsu.com>

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From: "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>
To: Alexander Lakhin <exclusion@gmail.com>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Masahiko Sawada <sawada.mshk@gmail.com>, Amit Kapila <amit.kapila16@gmail.com>
Date: 2023-04-26T10:41:22Z
Lists: pgsql-hackers

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On Wednesday, April 26, 2023 5:00 PM Alexander Lakhin <exclusion@gmail.com> wrote:
> Please look at a new anomaly that can be observed starting from 216a7848.
> 
> The following script:
> echo "CREATE SUBSCRIPTION testsub CONNECTION 'dbname=nodb'
> PUBLICATION testpub WITH (connect = false);
> ALTER SUBSCRIPTION testsub ENABLE;" | psql
> 
> sleep 1
> rm $PGINST/lib/libpqwalreceiver.so
> sleep 15
> pg_ctl -D "$PGDB" stop -m immediate
> grep 'TRAP:' server.log
> 
> Leads to multiple assertion failures:
> CREATE SUBSCRIPTION
> ALTER SUBSCRIPTION
> waiting for server to shut down.... done
> server stopped
> TRAP: failed Assert("MyProc->backendId != InvalidBackendId"), File: "lock.c",
> Line: 4439, PID: 2899323
> TRAP: failed Assert("MyProc->backendId != InvalidBackendId"), File: "lock.c",
> Line: 4439, PID: 2899416
> TRAP: failed Assert("MyProc->backendId != InvalidBackendId"), File: "lock.c",
> Line: 4439, PID: 2899427
> TRAP: failed Assert("MyProc->backendId != InvalidBackendId"), File: "lock.c",
> Line: 4439, PID: 2899439
> TRAP: failed Assert("MyProc->backendId != InvalidBackendId"), File: "lock.c",
> Line: 4439, PID: 2899538
> TRAP: failed Assert("MyProc->backendId != InvalidBackendId"), File: "lock.c",
> Line: 4439, PID: 2899547
> 
> server.log contains:
> 2023-04-26 11:00:58.797 MSK [2899300] LOG:  database system is ready to
> accept connections
> 2023-04-26 11:00:58.821 MSK [2899416] ERROR:  could not access file
> "libpqwalreceiver": No such file or directory
> TRAP: failed Assert("MyProc->backendId != InvalidBackendId"), File: "lock.c",
> Line: 4439, PID: 2899416
> postgres: logical replication apply worker for subscription 16385
> (ExceptionalCondition+0x69)[0x558b2ac06d41]
> postgres: logical replication apply worker for subscription 16385
> (VirtualXactLockTableCleanup+0xa4)[0x558b2aa9fd74]
> postgres: logical replication apply worker for subscription 16385
> (LockReleaseAll+0xbb)[0x558b2aa9fe7d]
> postgres: logical replication apply worker for subscription 16385
> (+0x4588c6)[0x558b2aa2a8c6]
> postgres: logical replication apply worker for subscription 16385
> (shmem_exit+0x6c)[0x558b2aa87eb1]
> postgres: logical replication apply worker for subscription 16385
> (+0x4b5faa)[0x558b2aa87faa]
> postgres: logical replication apply worker for subscription 16385
> (proc_exit+0xc)[0x558b2aa88031]
> postgres: logical replication apply worker for subscription 16385
> (StartBackgroundWorker+0x147)[0x558b2aa0b4d9]
> postgres: logical replication apply worker for subscription 16385
> (+0x43fdc1)[0x558b2aa11dc1]
> postgres: logical replication apply worker for subscription 16385
> (+0x43ff3d)[0x558b2aa11f3d]
> postgres: logical replication apply worker for subscription 16385
> (+0x440866)[0x558b2aa12866]
> postgres: logical replication apply worker for subscription 16385
> (+0x440e12)[0x558b2aa12e12]
> postgres: logical replication apply worker for subscription 16385
> (BackgroundWorkerInitializeConnection+0x0)[0x558b2aa14396]
> postgres: logical replication apply worker for subscription 16385
> (main+0x21a)[0x558b2a932e21]
> 
> I understand, that removing libpqwalreceiver.so (or whole pginst/) is not
> what happens in a production environment every day, but nonetheless it's a
> new failure mode and it can produce many coredumps when testing.
> 
> IIUC, that assert will fail in case of any error raised between
> ApplyWorkerMain()->logicalrep_worker_attach()->before_shmem_exit() and
> ApplyWorkerMain()->InitializeApplyWorker()->BackgroundWorkerInitializeC
> onnectionByOid()->InitPostgres().

Thanks for reporting the issue.

I think the problem is that it tried to release locks in
logicalrep_worker_onexit() before the initialization of the process is complete
because this callback function was registered before the init phase. So I think we
can add a conditional statement before releasing locks. Please find an attached
patch.

Best Regards,
Hou zj

Commits

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

  1. Fix invalid memory access during the shutdown of the parallel apply worker.

  2. Fix assertion failure in apply worker.

  3. Use elog to report unexpected action in handle_streamed_transaction().

  4. Use appropriate wait event when sending data in the apply worker.

  5. Allow the logical_replication_mode to be used on the subscriber.

  6. Rename GUC logical_decoding_mode to logical_replication_mode.

  7. Display the leader apply worker's PID for parallel apply workers.

  8. Improve the code to decide and process the apply action.

  9. Document the newly added wait events added by commit 216a784829.

  10. Perform apply of large transactions by parallel workers.

  11. Wake up a subscription's replication worker processes after DDL.

  12. Add copyright notices to meson files

  13. Better document logical replication parameters

  14. Add a common function to generate the origin name.

  15. Harmonize parameter names in storage and AM code.

  16. Avoid using list_length() to test for empty list.

  17. Improve two comments related to a boolean DefElem's value

  18. Fix partition table's REPLICA IDENTITY checking on the subscriber.

  19. Fix data inconsistency between publisher and subscriber.

  20. Fix cache look-up failures while applying changes in logical replication.