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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: "houzj.fnst@fujitsu.com" <houzj.fnst@fujitsu.com>
To: Amit Kapila <amit.kapila16@gmail.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>
Date: 2022-09-05T13:04:33Z
Lists: pgsql-hackers

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On Monday, September 5, 2022 8:41 PM houzj.fnst@fujitsu.com <houzj.fnst@fujitsu.com> wrote:
> 
> On Friday, September 2, 2022 2:10 PM Amit Kapila <amit.kapila16@gmail.com>
> wrote:
> >
> > On Thu, Sep 1, 2022 at 4:53 PM houzj.fnst@fujitsu.com
> > <houzj.fnst@fujitsu.com> wrote:
> > >
> >
> > Review of v27-0001*:
> 
> Thanks for the comments.
> 
> > ================
> > 1. I feel the usage of in_remote_transaction and in_use flags is slightly complex.
> > IIUC, the patch uses in_use flag to ensure commit ordering by waiting
> > for it to become false before proceeding in transaction finish
> > commands in leader apply worker. If so, I think it is better to name
> > it in_parallel_apply_xact and set it to true only when we start
> > applying xact in parallel apply worker and set it to false when we
> > finish the xact in parallel apply worker. It can be initialized to
> > false while setting up DSM. Also, accordingly change the function
> > parallel_apply_wait_for_free() to parallel_apply_wait_for_xact_finish
> > and parallel_apply_set_idle to parallel_apply_set_xact_finish. We can
> > change the name of the in_remote_transaction flag to in_use.
> 
> Agreed. One thing I found when addressing this is that there could be a race
> condition if we want to set the flag in parallel apply worker:
> 
> where the leader has already started waiting for the parallel apply worker to
> finish processing the transaction(set the in_parallel_apply_xact to false) while the
> child process has not yet processed the first STREAM_START and has not set the
> in_parallel_apply_xact to true.

Sorry, I didn’t complete this sentence. I meant it's safer to set this flag in apply leader,
So I changed the code like that and added some comments to explain the same.

...
> 
> Attach the new version patch set which addressed above comments and also
> fixed another problem while subscriber to a low version publisher.

Attach the correct patch set this time.

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.