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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: "houzj.fnst@fujitsu.com" <houzj.fnst@fujitsu.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: 2022-11-28T13:10:42Z
Lists: pgsql-hackers 
On Mon, Nov 28, 2022 at 12:49 PM Peter Smith <smithpb2250@gmail.com> wrote:
>
...
>
> 17.
> @@ -388,10 +401,9 @@ static inline void cleanup_subxact_info(void);
>  /*
>   * Serialize and deserialize changes for a toplevel transaction.
>   */
> -static void stream_cleanup_files(Oid subid, TransactionId xid);
>  static void stream_open_file(Oid subid, TransactionId xid,
>   bool first_segment);
> -static void stream_write_change(char action, StringInfo s);
> +static void stream_write_message(TransactionId xid, char action, StringInfo s);
>  static void stream_close_file(void);
>
> 17a.
>
> I felt just saying "file/files" is too vague. All the references to
> the file should be consistent, so IMO everything would be better named
> like:
>
> "stream_cleanup_files" -> "stream_msg_spoolfile_cleanup()"
> "stream_open_file" ->  "stream_msg_spoolfile_open()"
> "stream_close_file" -> "stream_msg_spoolfile_close()"
> "stream_write_message" -> "stream_msg_spoolfile_write_msg()"
>
> ~
>
> 17b.
> IMO there is not enough distinction here between function names
> stream_write_message and stream_write_change. e.g. You cannot really
> tell from their names what might be the difference.
>
> ~~~
>

I think the only new function needed by this patch is
stream_write_message so don't see why to change all others for that. I
see two possibilities to make name better (a) name function as
stream_open_and_write_change, or (b) pass a new argument (boolean
open) to stream_write_change

...
>
> src/include/replication/worker_internal.h
>
> 33. LeaderFileSetState
>
> +/* State of fileset in leader apply worker. */
> +typedef enum LeaderFileSetState
> +{
> + LEADER_FILESET_UNKNOWN,
> + LEADER_FILESET_BUSY,
> + LEADER_FILESET_ACCESSIBLE
> +} LeaderFileSetState;
>
> 33a.
>
> Missing from typedefs.list?
>
> ~
>
> 33b.
>
> I thought some more explanatory comments for the meaning of
> BUSY/ACCESSIBLE should be here.
>
> ~
>
> 33c.
>
> READY might be a better value than ACCESSIBLE
>
> ~
>
> 33d.
> I'm not sure what usefulness does the "LEADER_" and "Leader" prefixes
> give here. Maybe a name like PartialFileSetStat is more meaningful?
>
> e.g. like this?
>
> typedef enum PartialFileSetState
> {
> FS_UNKNOWN,
> FS_BUSY,
> FS_READY
> } PartialFileSetState;
>
> ~
>

All your suggestions in this point look good to me.

>
> ~~~
>
>
> 35. globals
>
>   /*
> + * Indicates whether the leader apply worker needs to serialize the
> + * remaining changes to disk due to timeout when sending data to the
> + * parallel apply worker.
> + */
> + bool serialize_changes;
>
> 35a.
> I wonder if the comment would be better to also mention "via shared memory".
>
> SUGGESTION
>
> Indicates whether the leader apply worker needs to serialize the
> remaining changes to disk due to timeout when attempting to send data
> to the parallel apply worker via shared memory.
>
> ~
>

I think the comment should say " .. the leader apply worker serialized
remaining changes ..."

> 35b.
> I wonder if a more informative variable name might be
> serialize_remaining_changes?
>

I think this needlessly makes the variable name long.

-- 
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.