Re: Question about commit 11cf92f6e2e13c0a6e3f98be3e629e6bd90b74d5

On Tue, Mar 5, 2019 at 3:00 AM Etsuro Fujita
<fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp> wrote:
> apply_projection_to_path() not only jams the given tlist into the
> existing path but updates its tlist eval costs appropriately except for
> the cases of Gather and GatherMerge:

I had forgotten that detail, but I don't think it changes the basic
picture. Once you've added a bunch of Paths to a RelOptInfo, it's too
late to change their *relative* cost, because add_path() puts the list
in a certain order, and adjusting the path costs won't change that
ordering. You've got to have the costs already correct at the time
add_path() is first called for any given Path.

--
Robert Haas
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