Try to exclude partitioned tables in toto.

Ashutosh Bapat, reviewed by Jeevan Chalke.  Comment by me.

Discussion: http://postgr.es/m/CAFjFpRcuRaydz88CY_aQekmuvmN2A9ax5z0k=ppT+s8KS8xMRA@mail.gmail.com

src/backend/optimizer/util/plancat.c

@@ -1414,8 +1414,18 @@ relation_excluded_by_constraints(PlannerInfo *root,
 	if (predicate_refuted_by(safe_restrictions, safe_restrictions, false))
 		return true;
 
-	/* Only plain relations have constraints */
-	if (rte->rtekind != RTE_RELATION || rte->inh)
+	/*
+	 * Only plain relations have constraints.  In a partitioning hierarchy,
+	 * but not with regular table inheritance, it's OK to assume that any
+	 * constraints that hold for the parent also hold for every child; for
+	 * instance, table inheritance allows the parent to have constraints
+	 * marked NO INHERIT, but table partitioning does not.  We choose to check
+	 * whether the partitioning parents can be excluded here; doing so
+	 * consumes some cycles, but potentially saves us the work of excluding
+	 * each child individually.
+	 */
+	if (rte->rtekind != RTE_RELATION ||
+		(rte->inh && rte->relkind != RELKIND_PARTITIONED_TABLE))
 		return false;
 
 	/*