On Thu, Sep 10, 2015 at 11:36 PM, Etsuro Fujita <fujita.ets...@lab.ntt.co.jp> wrote: > I've proposed the following API changes: > > * I modified create_foreignscan_path, which is called from > postgresGetForeignJoinPaths/postgresGetForeignPaths, so that a path, > subpath, is passed as the eighth argument of the function. subpath > represents a local join execution path if scanrelid==0, but NULL if > scanrelid>0.
OK, I see now. But I don't much like the way get_unsorted_unparameterized_path() looks. First, it's basically praying that MergePath, NodePath, and NestPath can be flat-copied without breaking anything. In general, we have copyfuncs.c support for nodes that we need to be able to copy, and we use copyObject() to do it. Even if what you've got here works today, it's not very future-proof. Second, what guarantee do we have that we'll find a path with no pathkeys and a NULL param_info? Why can't all of the paths for a join relation have pathkeys? Why can't they all be parameterized? I can't think of anything that would guarantee that. Third, even if such a guarantee existed, why is this the right behavior? Any join type will produce the same output; it's just a question of performance. And if you have only one tuple on each side, surely a nested loop would be fine. It seems to me that what you ought to be doing is using data hung off the fdw_private field of each RelOptInfo to cache a NestPath that can be used for EPQ rechecks at that level. When you go to consider pushing down another join, you can build up a new NestPath that's suitable for the new level. That seems much cleaner than groveling through the list of surviving paths and hoping you find the right kind of thing. And all that having been said, I still don't really understand why you are resisting the idea of providing a callback so that the FDW can execute arbitrary code in the recheck path. There doesn't seem to be any reason not to let the FDW take control of the rechecks if it wishes, and there's no real cost in complexity that I can see. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (email@example.com) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers