Github user hvanhovell commented on a diff in the pull request:
https://github.com/apache/spark/pull/17240#discussion_r105368556
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/CostBasedJoinReorder.scala
---
@@ -122,46 +123,59 @@ case class CostBasedJoinReorder(conf: CatalystConf)
extends Rule[LogicalPlan] wi
* level 3: p({A, B, C, D})
* where p({A, B, C, D}) is the final output plan.
*
- * For cost evaluation, since physical costs for operators are not
available currently, we use
- * cardinalities and sizes to compute costs.
+ * To evaluate cost for a given plan, we calculate the sum of
cardinalities for all intermediate
+ * joins in the plan.
*/
object JoinReorderDP extends PredicateHelper {
def search(
conf: CatalystConf,
items: Seq[LogicalPlan],
- conditions: Set[Expression],
- topOutput: AttributeSet): Option[LogicalPlan] = {
+ conditions: Set[Expression]): Option[LogicalPlan] = {
// Level i maintains all found plans for i + 1 items.
// Create the initial plans: each plan is a single item with zero cost.
- val itemIndex = items.zipWithIndex
+ val itemIndex = items.zipWithIndex.map(e => (e._2, e._1)).toMap
--- End diff --
NIT: use swap: `items.zipWithIndex.map(_.swap).toMap`
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