Re: Asynchronous MergeAppend

Hi.

Looked at it. Overall I agree that when we wait for data from one slot 
after node initialization, we can't get data from other slots - they are 
already either exhausted, or have already received data which is not 
needed for now. So it seems that async machinery on later stages is 
useless.

Was a bit surprised that asyncresults field is not used in async merge 
append anymore, as we save result directly in ms_slots. However, as we 
do it only on initial stage, this seems to be OK.

classify_matching_subplans() comment still refers to ms_valid_subplans.

Will look at it once again tomorrow.
-- 
Best regards,
Alexander Pyhalov,
Postgres Professional