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

On Monday, February 6, 2023 6:34 PM Kuroda, Hayato <kuroda(dot)hayato(at)fujitsu(dot)com> wrote:
> > while reading the code, I noticed that in pa_send_data() we set wait
> > event to WAIT_EVENT_LOGICAL_PARALLEL_APPLY_STATE_CHANGE while
> sending
> > the message to the queue. Because this state is used in multiple
> > places, user might not be able to distinguish what they are waiting
> > for. So It seems we'd better to use WAIT_EVENT_MQ_SEND here which will
> > be eaier to distinguish and understand. Here is a tiny patch for that.
>
> In LogicalParallelApplyLoop(), we introduced the new wait event
> WAIT_EVENT_LOGICAL_PARALLEL_APPLY_MAIN whereas it is practically waits a
> shared message queue and it seems to be same as WAIT_EVENT_MQ_RECEIVE.
> Do you have a policy to reuse the event instead of adding a new event?

I think PARALLEL_APPLY_MAIN waits for two kinds of event: 1) wait for new
message from the queue 2) wait for the partial file state to be set. So, I
think introducing a new general event for them is better and it is also
consistent with the WAIT_EVENT_LOGICAL_APPLY_MAIN which is used in the main
loop of leader apply worker(LogicalRepApplyLoop). But the event in
pg_send_data() is only for message send, so it seems fine to use
WAIT_EVENT_MQ_SEND, besides MQ_SEND is also unique in parallel apply worker and
user can distinglish without adding new event.

Best Regards,
Hou zj