Re: make add_paths_to_append_rel aware of startup cost

On Wed, Oct 4, 2023 at 8:41 AM David Rowley <dgrowleyml@gmail.com> wrote:

> On Sun, 1 Oct 2023 at 21:26, Andy Fan <zhihui.fan1213@gmail.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
>

Patch LGTM.

-- 
Best Regards
Andy Fan