Hi, There's code in add_paths_to_joinrel() which computes the set of target relations that should overlap parameterization of any proposed join path.
120 /* 121 * Decide whether it's sensible to generate parameterized paths for this 122 * joinrel, and if so, which relations such paths should require. There 123 * is usually no need to create a parameterized result path unless there 124 * is a join order restriction that prevents joining one of our input rels 125 * directly to the parameter source rel instead of joining to the other 126 * input rel. (But see allow_star_schema_join().) This restriction 127 * reduces the number of parameterized paths we have to deal with at 128 * higher join levels, without compromising the quality of the resulting 129 * plan. We express the restriction as a Relids set that must overlap the 130 * parameterization of any proposed join path. 131 */ The calculations that follow are based on joinrel->relids (baserels covered by the join) and SpecialJoinInfo list in PlannerInfo. It is not based on specific combination of relations being joined or the paths being generated. We should probably do this computation once and store the result in the joinrel and use it multiple times. That way we can avoid computing the same set again and again for every pair of joining relations and their order. Any reasons why we don't do this? Attached patch moves this code to build_join_rel() and uses it in add_paths_to_joinrel(). make check-world does not show any failures. If this change is acceptable, we might actually remove param_source_rels from JoinPathExtraData and directly access it from joinrel in try_nestloop_path(), try_mergejoin_path() and try_hashjoin_path(). Also, the way this code has been written, the declaration of variable sjinfo masks the earlier declaration with the same name. I am not sure if that's intentional, but may be we should use another variable name for the inner sjinfo. I have not included that change in the patch. -- Best Wishes, Ashutosh Bapat EnterpriseDB Corporation The Postgres Database Company
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