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

Wei Wang (Fujitsu) <wangw.fnst@fujitsu.com>

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From: "wangw.fnst@fujitsu.com" <wangw.fnst@fujitsu.com>
To: "shiy.fnst@fujitsu.com" <shiy.fnst@fujitsu.com>, Amit Kapila <amit.kapila16@gmail.com>
Cc: Masahiko Sawada <sawada.mshk@gmail.com>, Peter Smith <smithpb2250@gmail.com>, "houzj.fnst@fujitsu.com" <houzj.fnst@fujitsu.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2022-07-13T05:48:45Z
Lists: pgsql-hackers

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On Fri, Jul 7, 2022 at 11:32 AM Shi, Yu/侍 雨 <shiy.fnst@cn.fujitsu.com> wrote:
> Thanks for updating the patch.
> 
> Here are some comments.

Thanks for your comments.

> 0001 patch
> ==============
> 1.
> +	/* Check If there are free worker slot(s) */
> +	LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
> 
> I think "Check If" should be "Check if".

Fixed.

> 0003 patch
> ==============
> 1.
> Should we call apply_bgworker_relation_check() in apply_handle_truncate()?

Because TRUNCATE blocks all other operations on the table, I think that when
two transactions on the publisher-side operate on the same table, at least one
of them will be blocked. So I think for this case the blocking will happen on
the publisher-side.

> 0004 patch
> ==============
> 1.
> @@ -3932,6 +3958,9 @@ start_apply(XLogRecPtr origin_startpos)
>  	}
>  	PG_CATCH();
>  	{
> +		/* Set the flag that we will retry later. */
> +		set_subscription_retry(true);
> +
>  		if (MySubscription->disableonerr)
>  			DisableSubscriptionAndExit();
>  		Else
> 
> I think we need to emit the error and recover from the error state before
> setting the retry flag, like what we do in DisableSubscriptionAndExit().
> Otherwise if an error is detected when setting the retry flag, we won't get the
> error message reported by the apply worker.

You are right.
I fixed this point as you suggested. (I moved the operations you mentioned from
the function DisableSubscriptionAndExit to before setting the retry flag.)
I also made a similar modification in the function start_table_sync.

Attach the news patches.

Regards,
Wang wei

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.