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

Dilip Kumar <dilipbalaut@gmail.com>

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From: Dilip Kumar <dilipbalaut@gmail.com>
To: "houzj.fnst@fujitsu.com" <houzj.fnst@fujitsu.com>
Cc: Amit Kapila <amit.kapila16@gmail.com>, Masahiko Sawada <sawada.mshk@gmail.com>, "wangw.fnst@fujitsu.com" <wangw.fnst@fujitsu.com>, Peter Smith <smithpb2250@gmail.com>, "shiy.fnst@fujitsu.com" <shiy.fnst@fujitsu.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2023-01-05T11:53:36Z
Lists: pgsql-hackers 
On Thu, Jan 5, 2023 at 5:03 PM houzj.fnst@fujitsu.com
<houzj.fnst@fujitsu.com> wrote:
>
> On Thursday, January 5, 2023 4:22 PM Dilip Kumar <dilipbalaut@gmail.com> wrote:
> >

> Thanks for reporting the problem.
>
> After analyzing the behavior, I think it's a bug on publisher side which
> is not directly related to parallel apply.
>
> I think the root reason is that we didn't try to send a stream end(stream
> abort) message to subscriber for the crashed transaction which was streamed
> before.
> The behavior is that, after restarting, the publisher will start to decode the
> transaction that aborted due to crash, and when try to stream the first change
> of that transaction, it will send a stream start message but then it realizes
> that the transaction was aborted, so it will enter the PG_CATCH block of
> ReorderBufferProcessTXN() and call ReorderBufferResetTXN() which send the
> stream stop message. And in this case, there would be a parallel apply worker
> started on subscriber waiting for stream end message which will never come.

I suspected it but didn't analyze this.

> I think the same behavior happens for the non-parallel mode which will cause
> a stream file left on subscriber and will not be cleaned until the apply worker is
> restarted.
> To fix it, I think we need to send a stream abort message when we are cleaning
> up crashed transaction on publisher(e.g., in ReorderBufferAbortOld()). And here
> is a tiny patch which change the same. I have confirmed that the bug is fixed
> and all regression tests pass.
>
> What do you think ?
> I will start a new thread and try to write a testcase if possible
> after reaching a consensus.

I think your analysis looks correct and we can raise this in a new thread.


-- 
Regards,
Dilip Kumar
EnterpriseDB: http://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. 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.