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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: Dilip Kumar <dilipbalaut@gmail.com>, Amit Kapila <amit.kapila16@gmail.com>
Cc: 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: 2023-01-05T03:37:46Z
Lists: pgsql-hackers

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On Wednesday, January 4, 2023 9:29 PM Dilip Kumar <dilipbalaut@gmail.com> wrote:
> 
> On Wed, Jan 4, 2023 at 6:40 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
> >
> > On Wed, Jan 4, 2023 at 4:52 PM Dilip Kumar <dilipbalaut@gmail.com> wrote:
> > >
> > > 2.
> > > + * Since the database structure (schema of subscription tables,
> > > + constraints,
> > > + * etc.) of the publisher and subscriber could be different,
> > > + applying
> > > + * transactions in parallel mode on the subscriber side can cause
> > > + some
> > > + * deadlocks that do not occur on the publisher side.
> > >
> > > I think this paragraph needs to be rephrased a bit.  It is saying
> > > that some deadlock can occur on subscribers which did not occur on
> > > the publisher.  I think what it should be conveying is that the
> > > deadlock can occur due to concurrently applying the
> > > conflicting/dependent transactions which are not
> > > conflicting/dependent on the publisher due to <explain reason>.
> > > Because if we create the same schema on the publisher it might not
> > > have ended up in a deadlock instead it would have been executed in
> > > sequence (due to lock waiting). So the main point we are conveying
> > > is that the transaction which was independent of each other on the
> > > publisher could be dependent on the subscriber and they can end up in
> deadlock due to parallel apply.
> > >
> >
> > How about changing it to: "We have a risk of deadlock due to
> > parallelly applying the transactions that were independent on the
> > publisher side but became dependent on the subscriber side due to the
> > different database structures (like schema of subscription tables,
> > constraints, etc.) on each side.
> 
> I think this looks good to me.

Thanks for the comments.
Attach the new version patch set which changed the comments as suggested.

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.