Amit Kapila <amit.kapil...@gmail.com> writes: >>>> Is there some reason why hash and nestloop are safe but merge isn't?
> To make hash and nestloop work in parallel queries, we just push those > nodes below gather node. Refer code > paths match_unsorted_outer()->consider_parallel_nestloop() > and hash_inner_and_outer()->try_partial_hashjoin_path(). AFAICS, those are about generating partial paths, which is a completely different thing from whether a regular path is parallel-safe or not. (I think, anyway. It would be nice if this stuff were documented better. It would also likely be a good thing if partial-ness of a path were marked in the path itself, which does not seem to be the case now. Or at the very least, it'd be a good thing if create_foo_path and the underlying costing functions were told it was a partial path, because how the heck can they generate sane cost numbers without that knowledge?) regards, tom lane -- Sent via pgsql-hackers mailing list (email@example.com) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers