Re: postgres_fdw: wrong results with self join + enable_nestloop off

The commit[1] seems to break some queries in Citus[2], which is an extension which relies on set_join_pathlist_hook.

Although the comment says /*Finally, give extensions a chance to manipulate the path list.*/  we use it to extract lots of information about the joins and do the planning based on the information.

Now,  for some joins where consider_join_pushdown=false, we cannot get the information that we used to get, which prevents doing distributed planning for certain queries.

We wonder if it is possible to allow extensions to access the join info under all circumstances, as it used to be? Basically, removing the additional check:

diff --git a/src/backend/optimizer/path/joinpath.c b/src/backend/optimizer/path/joinpath.c
index 03b3185984..080e76cbe9 100644
--- a/src/backend/optimizer/path/joinpath.c
+++ b/src/backend/optimizer/path/joinpath.c
@@ -349,8 +349,7 @@ add_paths_to_joinrel(PlannerInfo *root,
        /*
         * 6. Finally, give extensions a chance to manipulate the path list.
         */
-       if (set_join_pathlist_hook &&
-               consider_join_pushdown)
+       if (set_join_pathlist_hook)
                set_join_pathlist_hook(root, joinrel, outerrel, innerrel,
                                                           jointype, &extra);
 }

Thanks,

Onder

[1]: https://github.com/postgres/postgres/commit/b0e390e6d1d68b92e9983840941f8f6d9e083fe0

[2]: https://github.com/citusdata/citus/issues/7119