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

On Thursday, January 26, 2023 11:37 AM Kuroda, Hayato/黒田 隼人 <kuroda(dot)hayato(at)fujitsu(dot)com> wrote:
>
> Followings are comments.

Thanks for the comments.

> In this test the rollback-prepared seems not to be executed. This is because
> serializations are finished while handling PREPARE message and the final
> state of transaction does not affect that, right? I think it may be helpful
> to add a one line comment.

Yes, but I am slightly unsure if it would be helpful to add this as we only test basic
cases(mainly for code coverage) for partial serialization.

>
> 1. config.sgml
>
> ```
> + the changes till logical_decoding_work_mem is reached. It can also
> be
> ```
>
> I think it should be sandwiched by <varname>.

Added.

>
> 2. config.sgml
>
> ```
> + On the publisher side,
> <varname>logical_replication_mode</varname> allows
> + allows streaming or serializing changes immediately in logical
> decoding.
> ```
>
> Typo "allows allows" -> "allows"

Fixed.

> 3. test general
>
> You confirmed that the leader started to serialize changes, but did not ensure
> the endpoint.
> IIUC the parallel apply worker exits after applying serialized changes, and it is
> not tested yet.
> Can we add polling the log somewhere?

I checked other tests and didn't find some examples where we test the exit of
apply worker or table sync worker. And if the parallel apply worker doesn't stop in
this case, we will fail anyway when reusing this worker to handle the next
transaction because the queue is broken. So, I prefer to keep the tests short.

> 4. 015_stream.pl
>
> ```
> +is($result, qq(15000), 'all changes are replayed from file')
> ```
>
> The statement may be unclear because changes can be also replicated when
> streaming = on.
> How about: "parallel apply worker replayed all changes from file"?

Changed.

Best regards,
Hou zj