Horton
Menu

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

Peter Smith <smithpb2250@gmail.com>

View thread
From: Peter Smith <smithpb2250@gmail.com>
To: Masahiko Sawada <sawada.mshk@gmail.com>
Cc: "houzj.fnst@fujitsu.com" <houzj.fnst@fujitsu.com>, Amit Kapila <amit.kapila16@gmail.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: 2022-11-18T02:30:43Z
Lists: pgsql-hackers 
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.
>

FWIW, I tend to agree with this idea but for a different reason. In
this patch, the 'streaming' parameter had become a kind of hybrid
boolean/enum. AFAIK there are no other parameters anywhere that use a
hybrid pattern like this so I was thinking it may be better not to be
different.

But I didn't think that parallel_apply=on should *require*
streaming=on. It might be better for parallel_apply=on is just the
*default*, but it simply achieves nothing unless streaming=on too.
That way users would not need to change anything at all to get the
benefits of parallel streaming.

> Another variant is to have a new subscription parameter for example
> "parallel_workers" parameter that specifies the number of parallel
> workers. That way, users can specify the number of parallel workers
> per subscription.
>

------
Kind Regards,
Peter Smith.
Fujitsu Australia.

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.