On Mon, Nov 6, 2017 at 9:57 PM, Amit Kapila <amit.kapil...@gmail.com> wrote: >> Well, I suppose that test will fire for a baserel when the total >> number of baserels is at least 3 and there's no inheritance involved. >> But if there are 2 baserels, we're still not the topmost scan/join >> target. > > No, if there are 2 baserels, then simple_rel_array_size will be 3. > The simple_rel_array_size is always the "number of relations" plus > "one". See setup_simple_rel_arrays.
Oh, wow. That's surprising. >> Also, even if inheritance is used, we might still be the >> topmost scan/join target. > > Sure, but in that case, it won't generate the gather path here (due to > this part of check "!root->append_rel_list"). I am not sure whether I > have understood the second part of your question, so if my answer > appears inadequate, then can you provide more details on what you are > concerned about? I don't know why the question of why root->append_rel_list is empty is the relevant thing here for deciding whether to generate gather paths at this point. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (firstname.lastname@example.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers