Re: make add_paths_to_append_rel aware of startup cost

Hi David,

But overall, I'm more inclined to just go with the more simple "add a
> cheap unordered startup append path if considering cheap startup
> plans" version. I see your latest patch does both. So, I'd suggest two
> patches as I do see the merit in keeping this simple and cheap. If we
> can get the first part in and you still find cases where you're not
> getting the most appropriate startup plan based on the tuple fraction,
> then we can reconsider what extra complexity we should endure in the
> code based on the example query where we've demonstrated the planner
> is not choosing the best startup path appropriate to the given tuple
> fraction.
>

I think this is a fair point, I agree that your first part is good enough
to be
committed first. Actually I tried a lot to make a test case which can
prove
the value of cheapest fractional cost but no gain so far:(

--
Best Regards
Andy Fan