On Thu, Jun 16, 2016 at 12:16 PM, Robert Haas <robertmh...@gmail.com> wrote: > On Thu, Jun 16, 2016 at 8:00 AM, Amit Kapila <amit.kapil...@gmail.com> wrote: >>> 1. The case originally reported by Thomas Munro still fails. To fix >>> that, we probably need to apply scanjoin_target to each partial path. >>> But we can only do that if it's parallel-safe. It seems like what we >>> want is something like this: (1) During scan/join planning, somehow >>> skip calling generate_gather_paths for the topmost scan/join rel as we >>> do to all the others. (2) If scanjoin_target is not parallel-safe, >>> build a path for the scan/join phase that applies a Gather node to the >>> cheapest path and does projection at the Gather node. Then forget all >>> the partial paths so we can't do any bogus upper planning. (3) If >>> scanjoin_target is parallel-safe, replace the list of partial paths >>> for the topmost scan/join rel with a new list where scanjoin_target >>> has been applied to each one. I haven't tested this so I might be >>> totally off-base about what's actually required here... >> >> I think we can achieve it just by doing something like what you have >> mentioned in (2) and (3). I am not sure if there is a need to skip >> generation of gather paths for top scan/join node. Please see the patch >> attached. I have just done some minimal testing to ensure that problem >> reported by Thomas Munro in this thread is fixed and verified that the fix >> is sane for problems [1][2] reported by sqlsmith. If you think this is on >> right lines, I can try to do more verification and try to add tests. > > You can't do it this way because of the issue Tom discussed here: > > https://www.postgresql.org/message-id/16421.1465828...@sss.pgh.pa.us
Something like what you have there might work if you use create_projection_path instead of apply_projection_to_path. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
