Github user cloud-fan commented on a diff in the pull request: https://github.com/apache/spark/pull/17286#discussion_r106582668 --- Diff: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/CostBasedJoinReorder.scala --- @@ -185,11 +184,14 @@ object JoinReorderDP extends PredicateHelper { // Should not join two overlapping item sets. if (oneSidePlan.itemIds.intersect(otherSidePlan.itemIds).isEmpty) { val joinPlan = buildJoin(oneSidePlan, otherSidePlan, conf, conditions, topOutput) - // Check if it's the first plan for the item set, or it's a better plan than - // the existing one due to lower cost. - val existingPlan = nextLevel.get(joinPlan.itemIds) - if (existingPlan.isEmpty || joinPlan.cost.lessThan(existingPlan.get.cost)) { - nextLevel.update(joinPlan.itemIds, joinPlan) + if (joinPlan.isDefined) { --- End diff -- when will this condition be false?
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