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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: Peter Smith <smithpb2250@gmail.com>
Cc: "wangw.fnst@fujitsu.com" <wangw.fnst@fujitsu.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: 2022-09-21T11:40:00Z
Lists: pgsql-hackers 
On Wed, Sep 21, 2022 at 2:55 PM Peter Smith <smithpb2250@gmail.com> wrote:
>
> ======
>
> 3. .../replication/logical/applyparallelworker.c - parallel_apply_can_start
>
> +/*
> + * Returns true, if it is allowed to start a parallel apply worker, false,
> + * otherwise.
> + */
> +static bool
> +parallel_apply_can_start(TransactionId xid)
>
> Seems a slightly complicated comment for a simple boolean function.
>
> SUGGESTION
> Returns true/false if it is OK to start a parallel apply worker.
>

I think this is the style followed at some other places as well. So,
we can leave it.

>
> 6. src/backend/replication/logical/launcher.c  - logicalrep_worker_detach
>
>  logicalrep_worker_detach(void)
>  {
> + /* Stop the parallel apply workers. */
> + if (!am_parallel_apply_worker() && !am_tablesync_worker())
> + {
> + List    *workers;
> + ListCell   *lc;
>
> The condition is not very obvious. This is why I previously suggested
> adding another macro/function like 'isLeaderApplyWorker'.
>

How about having function a function am_leader_apply_worker() { ...
return OidIsValid(MyLogicalRepWorker->relid) &&
(MyLogicalRepWorker->apply_leader_pid == InvalidPid) ...}?

>
> 13. src/include/replication/worker_internal.h
>
> + /*
> + * Indicates whether the worker is available to be used for parallel apply
> + * transaction?
> + */
> + bool in_use;
>
> This comment seems backward for this member's name.
>
> SUGGESTION (something like...)
> Indicates whether this ParallelApplyWorkerInfo is currently being used
> by a parallel apply worker processing a transaction. (If this flag is
> false then it means the ParallelApplyWorkerInfo is available for
> re-use by another parallel apply worker.)
>

I am not sure if this is an improvement over the current. The current
comment appears reasonable to me as it is easy to follow.

-- 
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.