Michael Paquier <mich...@paquier.xyz> writes: > On Mon, Sep 03, 2018 at 06:59:10PM -0700, Noah Misch wrote: >> If you're going to keep this highly-simplified estimate, please expand the >> comment to say why it doesn't matter or what makes it hard to do better. The >> non-planunionor.c path for the same query computes its own estimate of the >> same underlying quantity. Though it may be too difficult in today's system, >> one could copy the competing path's row count estimate here. Perhaps it >> doesn't matter because higher-level processing already assumes equal row >> count >> among competitors?
> As there has been no replies to Noah's review for one month, I am > marking this patch as returned with feedback for now. FWIW, my problem with this patch is that I remain unconvinced of the basic correctness of the transform (specifically the unique-ification approach). Noah's points would be important to address if we were moving the patch towards commit, but I don't see much reason to put effort into it until we can think of a way to prove whether that works. regards, tom lane