Robert Haas <robertmh...@gmail.com> writes: > On Tue, Mar 17, 2015 at 10:11 AM, Kouhei Kaigai <kai...@ak.jp.nec.com> wrote: >> It might be an idea if foreign-scan path is not wiped out regardless of the >> estimated cost, we will be able to construct an entirely remote-join path >> even if intermediation path is expensive than local join. >> A problem is, how to distinct these special paths from usual paths that are >> eliminated on the previous stage once its path is more expensive.
> Any solution that is based on not eliminating paths that would > otherwise be discarded based on cost seems to me to be unlikely to be > feasible. We can't complicate the core path-cost-comparison stuff for > the convenience of FDW or custom-scan pushdown. I concur. I'm not even so worried about the cost of add_path as such; the real problem with not discarding paths as aggressively as possible is that it will result in a combinatorial explosion in the number of path combinations that have to be examined at higher join levels. regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers