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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: "kuroda.hayato@fujitsu.com" <kuroda.hayato@fujitsu.com>
Cc: Amit Kapila <amit.kapila16@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>, Peter Smith <smithpb2250@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2022-09-26T03:09:55Z
Lists: pgsql-hackers

Attachments

On Thur, Sep 22, 2022 at 16:08 PM Kuroda, Hayato/黒田 隼人 <kuroda.hayato@fujitsu.com> wrote:
> Dear Wang,
> 
> Thanks for updating the patch! Followings are comments for v33-0001.

Thanks for your comments.

> ===
> libpqwalreceiver.c
> 
> 01. inclusion
> 
> ```
> +#include "catalog/pg_subscription.h"
> ```
> 
> We don't have to include it because the analysis of parameters is done at caller.
> 
> ===
> launcher.c

Improved.

> 02. logicalrep_worker_launch()
> 
> ```
> +       /*
> +        * Return silently if the number of parallel apply workers reached the
> +        * limit per subscription.
> +        */
> +       if (is_subworker && nparallelapplyworkers >=
> max_parallel_apply_workers_per_subscription)
> ```
> 
> a.
> I felt that it might be kind if we output some debug messages.
> 
> b.
> The if statement seems to be more than 80 characters. You can move to new
> line around "nparallelapplyworkers >= ...".

Improved.

> ===
> applyparallelworker.c
> 
> 03. declaration
> 
> ```
> +/*
> + * Is there a message pending in parallel apply worker which we need to
> + * receive?
> + */
> +volatile bool ParallelApplyMessagePending = false;
> ```
> 
> I checked other flags that are set by signal handlers, their datatype seemed to
> be sig_atomic_t.
> Is there any reasons that you use normal bool? It should be changed if not.

Improved.

> 04. HandleParallelApplyMessages()
> 
> ```
> +               if (winfo->error_mq_handle == NULL)
> +                       continue;
> ```
> 
> a.
> I was not sure when the cell should be cleaned. Currently we clean up
> ParallelApplyWorkersList() only in the parallel_apply_start_worker(),
> but we have chances to remove such a cell like HandleParallelApplyMessages()
> or HandleParallelApplyMessage(). How do you think?
> 
> b.
> Comments should be added even if we keep this, like "exited worker, skipped".
> 
> ```
> +               else
> +                       ereport(ERROR,
> +
> (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
> +                                        errmsg("lost connection to the leader apply worker")));
> ```
> 
> c.
> This function is called on the leader apply worker, so the hint should be "lost
> connection to the parallel apply worker".

=>b.
Added the following comment according to your suggestion.
`Skip if worker has exited`

=>c.
Fixed.

> ===
> worker.c
> 
> 07. handle_streamed_transaction()
> 
> ```
> + * For non-streamed transactions, returns false;
> ```
> 
> "returns false;" -> "returns false"

Improved. I changed the semicolon to a period

> apply_handle_commit_prepared(), apply_handle_abort_prepared()
> 
> These functions are not expected that parallel worker calls
> so I think Assert() should be added.

I am not sure if this modification is necessary since we do not modify the
non-streamed transaction related message like "COMMIT PREPARED" or "ROLLBACK
PREPARED".

> 08. UpdateWorkerStats()
> 
> ```
> -static void
> +void
>  UpdateWorkerStats(XLogRecPtr last_lsn, TimestampTz send_time, bool reply)
> ```
> 
> This function is called only in worker.c, should be static.
> 
> 09. subscription_change_cb()
> 
> ```
> -static void
> +void
>  subscription_change_cb(Datum arg, int cacheid, uint32 hashvalue)
> ```
> 
> This function is called only in worker.c, should be static.

Improved.

> 10. InitializeApplyWorker()
> 
> ```
> +/*
> + * Initialize the database connection, in-memory subscription and necessary
> + * config options.
> + */
>  void
> -ApplyWorkerMain(Datum main_arg)
> +InitializeApplyWorker(void)
> ```
> 
> Some comments should be added about this is a common part of leader and
> parallel apply worker.

Added the following comment:
`The common initialization for leader apply worker and parallel apply worker.`

> ===
> logicalrepworker.h
> 
> 11. declaration
> 
> ```
> extern PGDLLIMPORT volatile bool ParallelApplyMessagePending;
> ```
> 
> Please refer above comment.
> 
> ===
> guc_tables.c

Improved.

Also rebased the patch set based on the changes in HEAD (26f7802).

Attach the new patch set.

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.