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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: "houzj.fnst@fujitsu.com" <houzj.fnst@fujitsu.com>
Cc: Masahiko Sawada <sawada.mshk@gmail.com>, "wangw.fnst@fujitsu.com" <wangw.fnst@fujitsu.com>, Peter Smith <smithpb2250@gmail.com>, Dilip Kumar <dilipbalaut@gmail.com>, "shiy.fnst@fujitsu.com" <shiy.fnst@fujitsu.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2022-11-30T10:53:50Z
Lists: pgsql-hackers

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On Tue, Nov 29, 2022 at 10:18 AM houzj.fnst@fujitsu.com
<houzj.fnst@fujitsu.com> wrote:
>
> Attach the new version patch which addressed all comments.
>

Some comments on v53-0002*
========================
1. I think testing the scenario where the shm_mq buffer is full
between the leader and parallel apply worker would require a large
amount of data and then also there is no guarantee. How about having a
developer GUC [1] force_apply_serialize which allows us to serialize
the changes and only after commit the parallel apply worker would be
allowed to apply it?

I am not sure if we can reliably test the serialization of partial
changes (like some changes have been already sent to parallel apply
worker and then serialization happens) but at least we can test the
serialization of complete xacts and their execution via parallel apply
worker.

2.
+ /*
+ * The stream lock is released when processing changes in a
+ * streaming block, so the leader needs to acquire the lock here
+ * before entering PARTIAL_SERIALIZE mode to ensure that the
+ * parallel apply worker will wait for the leader to release the
+ * stream lock.
+ */
+ if (in_streamed_transaction &&
+ action != LOGICAL_REP_MSG_STREAM_STOP)
+ {
+ pa_lock_stream(winfo->shared->xid, AccessExclusiveLock);

This comment is not completely correct because we can even acquire the
lock for the very streaming chunk. This check will work but doesn't
appear future-proof or at least not very easy to understand though I
don't have a better suggestion at this stage. Can we think of a better
check here?

3. I have modified a few comments in v53-0002* patch and the
incremental patch for the same is attached.

[1] - https://www.postgresql.org/docs/devel/runtime-config-developer.html

-- 
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.