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

On Mon, Nov 7, 2022 at 1:46 PM Peter Smith <smithpb2250(at)gmail(dot)com> wrote:
>
> Here are my review comments for v42-0001
...
...
>
> 8.
>
> + /*
> + * Resend the pending message to parallel apply worker to cleanup the
> + * queue. Note that parallel apply worker will just ignore this message
> + * as it has already handled this message while applying spooled
> + * messages.
> + */
> + result = shm_mq_send(winfo->mq_handle, strlen(winfo->pending_msg),
> + winfo->pending_msg, false, true);
>
> If I understand this logic it seems a bit hacky. From the comment, it
> seems you are resending a message that you know/expect to be ignored
> simply to make it disappear. (??). Isn't there some other way to clear
> the pending message without requiring a bogus send?
>

IIUC, this handling is required for the case when we are not able to
send a message to parallel apply worker and switch to serialize mode
(write remaining data to file). Basically, it is possible that the
message is only partially sent and there is no way clean the queue. I
feel we can directly free the worker in this case even if there is a
space in the worker pool. The other idea could be that we detach from
shm_mq and then invent a way to re-attach it after we try to reuse the
same worker.

--
With Regards,
Amit Kapila.