Re: make add_paths_to_append_rel aware of startup cost

On Sun, 1 Oct 2023 at 21:26, Andy Fan <zhihui(dot)fan1213(at)gmail(dot)com> wrote:
>> 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:(

I've attached a patch with the same code as the previous patch but
this time including a regression test.

I see no reason to not commit this so if anyone feels differently
please let me know.

David