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

Wei Wang (Fujitsu) <wangw.fnst@fujitsu.com>

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From: "wangw.fnst@fujitsu.com" <wangw.fnst@fujitsu.com>
To: Amit Kapila <amit.kapila16@gmail.com>
Cc: Peter Smith <smithpb2250@gmail.com>, "houzj.fnst@fujitsu.com" <houzj.fnst@fujitsu.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: 2022-09-26T03:11:38Z
Lists: pgsql-hackers 
On Thur, Sep 22, 2022 at 18:12 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
> Few comments on v33-0001
> =======================

Thanks for your comments.

> 1.
> + else if (data->streaming == SUBSTREAM_PARALLEL &&
> + data->protocol_version <
> LOGICALREP_PROTO_STREAM_PARALLEL_VERSION_NUM)
> + ereport(ERROR,
> + (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
> + errmsg("requested proto_version=%d does not support
> streaming=parallel mode, need %d or higher",
> + data->protocol_version,
> LOGICALREP_PROTO_STREAM_PARALLEL_VERSION_NUM)));
> 
> I think we can improve this error message as: "requested
> proto_version=%d does not support parallel streaming mode, need %d or
> higher".

Improved.

> 2.
> --- a/doc/src/sgml/monitoring.sgml
> +++ b/doc/src/sgml/monitoring.sgml
> @@ -3184,7 +3184,7 @@ SELECT pid, wait_event_type, wait_event FROM
> pg_stat_activity WHERE wait_event i
>        </para>
>        <para>
>         OID of the relation that the worker is synchronizing; null for the
> -       main apply worker
> +       main apply worker and the apply parallel worker
>        </para></entry>
>       </row>
> 
> This and other changes in monitoring.sgml refers the workers as "apply
> parallel worker". Isn't it better to use parallel apply worker as we
> are using at other places in the patch? But, I have another question,
> do we really need to display entries for parallel apply workers in
> pg_stat_subscription if it doesn't have any meaningful information? I
> think we can easily avoid it in pg_stat_get_subscription by checking
> apply_leader_pid.

Make sense. Improved as suggested.
Do not display parallel apply worker related information in this view after
applying 0001 patch. But display entries for parallel apply worker after
applying 0005 patch.

> 3.
> ApplyWorkerMain()
> {
> ...
> ...
> +
> + if (server_version >= 160000 &&
> + MySubscription->stream == SUBSTREAM_PARALLEL)
> + options.proto.logical.streaming = pstrdup("parallel");
> 
> After deciding here whether the parallel streaming mode is enabled or
> not, we recheck the same thing in apply_handle_stream_abort() and
> parallel_apply_can_start(). In parallel_apply_can_start(), we do it
> via two different checks. How about storing this information say in
> structure MyLogicalRepWorker in ApplyWorkerMain() and then use it at
> other places?

Improved as suggested.
Added a new flag "in_parallel_apply" to structure MyLogicalRepWorker.

Because the patch set could not be applied cleanly, I rebased and shared them
for review.
I have not addressed the comment you posted in [1]. I will share the new patch
set when I finish them.

The new patches were attached in [2].

[1] - https://www.postgresql.org/message-id/CAA4eK1KjGNA8T8O77rRhkv6bRT6OsdQaEy--2hNrJFCc80bN0A%40mail.gmail.com
[2] - https://www.postgresql.org/message-id/OS3PR01MB6275F4A7CA186412E2FF2ED29E529%40OS3PR01MB6275.jpnprd01.prod.outlook.com

Regards,
Wang wei

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.