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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: Amit Kapila <amit.kapila16@gmail.com>
Cc: Masahiko Sawada <sawada.mshk@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: 2022-12-07T02:58:19Z
Lists: pgsql-hackers

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On Tuesday, December 6, 2022 3:50 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
> 
> On Mon, Dec 5, 2022 at 9:59 AM houzj.fnst@fujitsu.com
> <houzj.fnst@fujitsu.com> wrote:
> >
> > Attach a new version patch set which fixed a testcase failure on CFbot.
> >
> 
> Few comments:
> ============
> 1.
> + /*
> + * Break the loop if the parallel apply worker has finished applying
> + * the transaction. The parallel apply worker should have closed the
> + * file before committing.
> + */
> + if (am_parallel_apply_worker() &&
> + MyParallelShared->xact_state == PARALLEL_TRANS_FINISHED)
> + goto done;
> 
> This looks hackish to me because ideally, this API should exit after reading and
> applying all the messages in the spool file. This check is primarily based on the
> knowledge that once we reach some state, the file won't have more data. I
> think it would be better to explicitly ensure the same.

I added a function to ensure that there is no message left after committing
the transaction.


> 2.
> + /*
> + * No need to output the DEBUG message here in the parallel apply
> + * worker as similar messages will be output when handling STREAM_STOP
> + * message.
> + */
> + if (!am_parallel_apply_worker() && nchanges % 1000 == 0)
>   elog(DEBUG1, "replayed %d changes from file \"%s\"",
>   nchanges, path);
>   }
> 
> I think this check appeared a bit ugly to me. I think it is okay to get a similar
> DEBUG message at another place (on stream_stop) because
> (a) this is logged every 1000 messages whereas stream_stop can be after many
> more messages, so there doesn't appear to be a direct correlation; (b) due to
> this, we can identify whether it is due to spooled messages or due to direct
> apply; ideally we can use another DEBUG message to differentiate but this
> doesn't appear bad to me.

OK, I removed this check.

> 3. The function names for serialize_stream_start(), serialize_stream_stop(), and
> serialize_stream_abort() don't seem to match the functionality they provide
> because none of these write/serialize changes to the file. Can we rename
> these? Some possible options could be stream_start_internal or
> stream_start_guts.

Renamed to stream_start_internal().

Attach the new version patch set which addressed above comments.
I also attach a new patch to force stream change(provided by Shi-san) and
another one that introduce a GUC stream_serialize_threshold (provided by
Kuroda-san and Shi-san) which can help testing the patch set.

Besides, I fixed a bug where there could still be messages left in memory
queue and the PA has started to apply spooled message.

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.