Robert Haas <robertmh...@gmail.com> writes: > On Fri, Aug 2, 2024 at 9:13 AM David Rowley <dgrowle...@gmail.com> wrote: >> ... That way you maintain the >> existing behaviour of not optimising for disabled node types and don't >> risk plan changes if the final cost comes out cheaper than the initial >> cost.
> All three initial_cost_XXX functions have a comment that says "This > must quickly produce lower-bound estimates of the path's startup and > total costs," i.e. the final cost should never be cheaper. I'm pretty > sure that it was the design intention here that no path ever gets > rejected at the initial cost stage that would have been accepted at > the final cost stage. That absolutely is the expectation, and we'd better be careful not to break it. regards, tom lane