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

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

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From: "kuroda.hayato@fujitsu.com" <kuroda.hayato@fujitsu.com>
To: "houzj.fnst@fujitsu.com" <houzj.fnst@fujitsu.com>
Cc: "wangw.fnst@fujitsu.com" <wangw.fnst@fujitsu.com>, Peter Smith <smithpb2250@gmail.com>, Dilip Kumar <dilipbalaut@gmail.com>, Masahiko Sawada <sawada.mshk@gmail.com>, "shiy.fnst@fujitsu.com" <shiy.fnst@fujitsu.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Amit Kapila <amit.kapila16@gmail.com>
Date: 2022-09-13T12:02:26Z
Lists: pgsql-hackers 
Dear Hou-san,

> I will dig your patch more, but I send partially to keep the activity of the thread.

More minor comments about v28.

===
About 0002 

For 015_stream.pl

14. check_parallel_log

```
+# Check the log that the streamed transaction was completed successfully
+# reported by parallel apply worker.
+sub check_parallel_log
+{
+       my ($node_subscriber, $offset, $is_parallel)= @_;
+       my $parallel_message = 'finished processing the transaction finish command';
+
+       if ($is_parallel)
+       {
+               $node_subscriber->wait_for_log(qr/$parallel_message/, $offset);
+       }
+}
```

I think check_parallel_log() should be called only when streaming = 'parallel' and if-statement is not needed

===
For 016_stream_subxact.pl

15. test_streaming

```
+       INSERT INTO test_tab SELECT i, md5(i::text) FROM generate_series(    3,  500) s(i);
```

"    3" should be "3".

===
About 0003

For applyparallelworker.c

16. parallel_apply_relation_check()

```
+       if (rel->parallel_apply_safe == PARALLEL_APPLY_SAFETY_UNKNOWN)
+               logicalrep_rel_mark_parallel_apply(rel);
```

I was not clear when logicalrep_rel_mark_parallel_apply() is called here.
IIUC parallel_apply_relation_check() is called when parallel apply worker handles changes,
but before that relation is opened via logicalrep_rel_open() and parallel_apply_safe is set here.
If it guards some protocol violation, we may use Assert().

===
For create_subscription.sgml

17.
The restriction about foreign key does not seem to be documented.

===
About 0004

For 015_stream.pl

18. check_parallel_log

I heard that the removal has been reverted, but in the patch
check_parallel_log() is removed again... :-(


===
About throughout

I checked the test coverage via `make coverage`. About appluparallelworker.c and worker.c, both function coverage is 100%, and
line coverages are 86.2 % and 94.5 %. Generally it's good.
But I read the report and following parts seems not tested.

In parallel_apply_start_worker():

```
		if (tmp_winfo->error_mq_handle == NULL)
		{
			/*
			 * Release the worker information and try next one if the parallel
			 * apply worker exited cleanly.
			 */
			ParallelApplyWorkersList = foreach_delete_current(ParallelApplyWorkersList, lc);
			shm_mq_detach(tmp_winfo->mq_handle);
			dsm_detach(tmp_winfo->dsm_seg);
			pfree(tmp_winfo);
		}
```

In HandleParallelApplyMessage():

```
		case 'X':				/* Terminate, indicating clean exit */
			{
				shm_mq_detach(winfo->error_mq_handle);
				winfo->error_mq_handle = NULL;
				break;
			}
```

Does it mean that we do not test the termination of parallel apply worker? If so I think it should be tested.

Best Regards,
Hayato Kuroda
FUJITSU LIMITED

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.