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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: Masahiko Sawada <sawada.mshk@gmail.com>
Cc: Amit Kapila <amit.kapila16@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: 2022-12-16T09:17:37Z
Lists: pgsql-hackers 
On Friday, December 16, 2022 3:08 PM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
> 
> 
>Here are some minor comments:

Thanks for the comments!

> ---
> +pa_has_spooled_message_pending()
> +{
> +       PartialFileSetState fileset_state;
> +
> +       fileset_state = pa_get_fileset_state();
> +
> +       if (fileset_state != FS_UNKNOWN)
> +               return true;
> +       else
> +               return false;
> +}
> 
> I think we can simply do:
> 
> return (fileset_state != FS_UNKNOWN);

Will change.

> 
> Or do we need this function in the first place? I think we can do in
> LogicalParallelApplyLoop() like:

I was intended to not expose the file state in the main loop, so maybe better
to keep this function.

> ---
> +       active_workers = list_copy(ParallelApplyWorkerPool);
> +
> +       foreach(lc, active_workers)
> +       {
> +               int                     slot_no;
> +               uint16          generation;
> +               ParallelApplyWorkerInfo *winfo =
> (ParallelApplyWorkerInfo *) lfirst(lc);
> +
> +               LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
> +               napplyworkers =
> logicalrep_pa_worker_count(MyLogicalRepWorker->subid);
> +               LWLockRelease(LogicalRepWorkerLock);
> +
> +               if (napplyworkers <=
> max_parallel_apply_workers_per_subscription / 2)
> +                       return;
> +
> 
> Calling logicalrep_pa_worker_count() with lwlock for each worker seems
> not efficient to me. I think we can get the number of workers once at
> the top of this function and return if it's already lower than the
> maximum pool size. Otherwise, we attempt to stop extra workers.

How about we directly check the length of worker pool list here which
seems simpler and don't need to lock ?

> ---
> +bool
> +pa_free_worker(ParallelApplyWorkerInfo *winfo, TransactionId xid)
> +{
> 
> 
> Is there any reason why this function has the XID as a separate
> argument? It seems to me that since we always call this function with
> 'winfo' and 'winfo->shared->xid', we can remove xid from the function
> argument.
> 
> ---
> +       /* Initialize shared memory area. */
> +       SpinLockAcquire(&winfo->shared->mutex);
> +       winfo->shared->xact_state = PARALLEL_TRANS_UNKNOWN;
> +       winfo->shared->xid = xid;
> +       SpinLockRelease(&winfo->shared->mutex);
> 
> It's practically no problem but is there any reason why some fields of
> ParallelApplyWorkerInfo are initialized in pa_setup_dsm() whereas some
> fields are done here?

We could be using old worker in the pool here in which case we need to update
these fields with the new streaming transaction information.

I will address other comments except above ones which are being discussed.

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.