Re: Asynchronous Append on postgres_fdw nodes.

Hello.

As the result of a discussion with Fujita-san off-list, I'm going to
hold off development until he decides whether mine or Thomas' is
better.

However, I fixed two misbehaviors and rebased.

A. It runs ordered Append asynchronously, but that leads to a bogus
result. I taught create_append_plan not to make subnodes async when
pathkey is not NIL.

B. It calculated the total cost of Append by summing up total costs of
all subnodes including async subnodes. It is too pessimistic so I
changed that to the following.

Max(total cost of sync subnodes, maximum cost of async subnodes);

However this is a bit too optimistic in that it ignores interference
between async subnodes, it is more realistic in the cases where the
subnode ForeignScans are connecting to different servers.

regards.

--
Kyotaro Horiguchi
NTT Open Source Software Center