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

Zhijie Hou (Fujitsu) <houzj.fnst@fujitsu.com>

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From: "houzj.fnst@fujitsu.com" <houzj.fnst@fujitsu.com>
To: Peter Smith <smithpb2250@gmail.com>
Cc: Amit Kapila <amit.kapila16@gmail.com>, Masahiko Sawada <sawada.mshk@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: 2022-12-04T11:18:29Z
Lists: pgsql-hackers 
On Friday, December 2, 2022 4:59 PM Peter Smith <smithpb2250@gmail.com> wrote:
> 
> Here are my review comments for patch v54-0001.

Thanks for the comments!

> ======
> 
> FILE: .../replication/logical/applyparallelworker.c
> 
> 1b.
> 
> + *
> + * This file contains routines that are intended to support setting up,
> + using
> + * and tearing down a ParallelApplyWorkerInfo which is required to
> + communicate
> + * among leader and parallel apply workers.
> 
> "that are intended to support" -> "for"

I find the current word is consistent with the comments atop vacuumparallel.c and
execParallel.c. So didn't change this one.

> 3. pa_setup_dsm
> 
> +/*
> + * Set up a dynamic shared memory segment.
> + *
> + * We set up a control region that contains a fixed-size worker info
> + * (ParallelApplyWorkerShared), a message queue, and an error queue.
> + *
> + * Returns true on success, false on failure.
> + */
> +static bool
> +pa_setup_dsm(ParallelApplyWorkerInfo *winfo)
> 
> IMO that's confusing to say "fixed-sized worker info" when it's referring to the
> ParallelApplyWorkerShared structure and not the other
> ParallelApplyWorkerInfo.
> 
> Might be better to say:
> 
> "a fixed-size worker info (ParallelApplyWorkerShared)" -> "a fixed-size struct
> (ParallelApplyWorkerShared)"

The ParallelApplyWorkerShared is also kind of information that shared
between workers. So, I am fine with current word. Or maybe just "fixed-size info" ?

> ~~~
> 
> 12. pa_clean_subtrans
> 
> +/* Reset the list that maintains subtransactions. */ void
> +pa_clean_subtrans(void)
> +{
> + subxactlist = NIL;
> +}
> 
> Maybe a more informative function name would be pa_reset_subxactlist()?

I thought the current name is more consistent with pa_start_subtrans.

> ~~~
> 
> 17. apply_handle_stream_stop
> 
> + case TRANS_PARALLEL_APPLY:
> + elog(DEBUG1, "applied %u changes in the streaming chunk",
> + parallel_stream_nchanges);
> +
> + /*
> + * By the time parallel apply worker is processing the changes in
> + * the current streaming block, the leader apply worker may have
> + * sent multiple streaming blocks. This can lead to parallel apply
> + * worker start waiting even when there are more chunk of streams
> + * in the queue. So, try to lock only if there is no message left
> + * in the queue. See Locking Considerations atop
> + * applyparallelworker.c.
> + */
> 
> SUGGESTION (minor rewording)
> 
> By the time the parallel apply worker is processing the changes in the current
> streaming block, the leader apply worker may have sent multiple streaming
> blocks. To the parallel apply from waiting unnecessarily, try to lock only if there
> is no message left in the queue. See Locking Considerations atop
> applyparallelworker.c.
> 

Didn't change this one according to Amit's comment.

> 
> 21. apply_worker_clean_exit
> 
> I wasn't sure if calling this a 'clean' exit meant anything much.
> 
> How about:
> - apply_worker_proc_exit, or
> - apply_worker_exit

I thought the clean means the exit number is 0(proc_exit(0)) and is
not due to any ERROR, I am not sure If proc_exit or exit is better.

I have addressed other comments in the new version patch.

Best regards,
Hou zj

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.