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

Amit Kapila <amit.kapila16@gmail.com>

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From: Amit Kapila <amit.kapila16@gmail.com>
To: Masahiko Sawada <sawada.mshk@gmail.com>
Cc: Peter Smith <smithpb2250@gmail.com>, "houzj.fnst@fujitsu.com" <houzj.fnst@fujitsu.com>, "wangw.fnst@fujitsu.com" <wangw.fnst@fujitsu.com>, Dilip Kumar <dilipbalaut@gmail.com>, "shiy.fnst@fujitsu.com" <shiy.fnst@fujitsu.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2022-11-18T05:07:14Z
Lists: pgsql-hackers 
On Fri, Nov 18, 2022 at 10:31 AM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
>
> On Fri, Nov 18, 2022 at 1:47 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
> >
> > On Fri, Nov 18, 2022 at 8:01 AM Peter Smith <smithpb2250@gmail.com> wrote:
> > >
> > > On Fri, Nov 18, 2022 at 11:36 AM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
> > > >
> > > ...
> > > > ---
> > > > The streaming parameter has the new value "parallel" for "streaming"
> > > > option to enable the parallel apply. It fits so far but I think the
> > > > parallel apply feature doesn't necessarily need to be tied up with
> > > > streaming replication. For example, we might want to support parallel
> > > > apply also for non-streaming transactions in the future. It might be
> > > > better to have another option, say "parallel", to control parallel
> > > > apply behavior. The "parallel" option can be a boolean option and
> > > > setting parallel = on requires streaming = on.
> > > >
> >
> > If we do that then how will the user be able to use streaming
> > serialize mode (write to file for streaming transactions) as we have
> > now? Because after we introduce parallelism for non-streaming
> > transactions, the user would want parallel = on irrespective of the
> > streaming mode. Also, users may wish to only parallelize large
> > transactions because of additional overhead for non-streaming
> > transactions for transaction dependency tracking, etc. So, the user
> > may wish to have a separate knob for large transactions as the patch
> > has now.
>
> One idea for that would be to make it enum. For example, setting
> parallel = "streaming" works for that.
>

Yeah, but then we will have two different parameters (parallel and
streaming) to control streaming behavior. This will be confusing say
when the user says parallel = 'streaming' and streaming = off, we need
to probably disallow such settings but not sure if it would be any
better than allowing parallelism for large xacts by streaming
parameter.

-- 
With Regards,
Amit Kapila.

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.