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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: "wangw.fnst@fujitsu.com" <wangw.fnst@fujitsu.com>
Cc: Dilip Kumar <dilipbalaut@gmail.com>, Peter Smith <smithpb2250@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>, "houzj.fnst@fujitsu.com" <houzj.fnst@fujitsu.com>
Date: 2022-08-10T02:11:21Z
Lists: pgsql-hackers 
Hi Wang,

> 6.a
> 
> It seems that the upper line represents the apply background worker, but I think
> last_msg_send_time and last_msg_receipt_time should be null.
> Is it like initialization mistake?

I checked again about the issue.

Attributes worker->last_send_time, worker->last_recv_time, and worker->reply_time
are initialized in logicalrep_worker_launch():

```
...
	TIMESTAMP_NOBEGIN(worker->last_send_time);
	TIMESTAMP_NOBEGIN(worker->last_recv_time);
	worker->reply_lsn = InvalidXLogRecPtr;
	TIMESTAMP_NOBEGIN(worker->reply_time);
...
```

And the macro is defined in timestamp.h, and it seems that the values are initialized as PG_INT64_MIN.

```
#define DT_NOBEGIN		PG_INT64_MIN
#define DT_NOEND		PG_INT64_MAX

#define TIMESTAMP_NOBEGIN(j)	\
	do {(j) = DT_NOBEGIN;} while (0)
```


However, in pg_stat_get_subscription(), these values are regarded as null if they are zero.

```
		if (worker.last_send_time == 0)
			nulls[4] = true;
		else
			values[4] = TimestampTzGetDatum(worker.last_send_time);
		if (worker.last_recv_time == 0)
			nulls[5] = true;
		else
			values[5] = TimestampTzGetDatum(worker.last_recv_time);
```

I think above lines are wrong, these values should be compared with PG_INT64_MIN.

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.