[GitHub] spark pull request: [SPARK-9066][SQL] Improve cartesian performanc...

[cloud-fan <gi...@git.apache.org>]

Github user cloud-fan commented on a diff in the pull request:

    https://github.com/apache/spark/pull/7417#discussion_r41081828
  
    --- Diff: sql/core/src/main/scala/org/apache/spark/sql/execution/SparkStrategies.scala ---
    @@ -274,12 +275,30 @@ private[sql] abstract class SparkStrategies extends QueryPlanner[SparkPlan] {
       }
     
       object CartesianProduct extends Strategy {
    +    def getSmallSide(left: LogicalPlan, right: LogicalPlan): BuildSide = {
    +      if (right.statistics.sizeInBytes < left.statistics.sizeInBytes) {
    +        joins.BuildRight
    +      } else {
    +        joins.BuildLeft
    +      }
    +    }
    +
         def apply(plan: LogicalPlan): Seq[SparkPlan] = plan match {
    +      // If plan can broadcast we use BroadcastNestedLoopJoin, as we know for inner join with true
    +      // condition is same as Cartesian.
    +      case logical.Join(CanBroadcast(left), right, joinType, condition) =>
    +        execution.joins.BroadcastNestedLoopJoin(
    +          planLater(left), planLater(right), joins.BuildLeft, joinType, condition) :: Nil
    +      case logical.Join(left, CanBroadcast(right), joinType, condition) =>
    +        execution.joins.BroadcastNestedLoopJoin(
    +          planLater(left), planLater(right), joins.BuildRight, joinType, condition) :: Nil
           case logical.Join(left, right, _, None) =>
    -        execution.joins.CartesianProduct(planLater(left), planLater(right)) :: Nil
    +        execution.joins.CartesianProduct(planLater(left), planLater(right),
    +          getSmallSide(left, right)) :: Nil
           case logical.Join(left, right, Inner, Some(condition)) =>
             execution.Filter(condition,
    -          execution.joins.CartesianProduct(planLater(left), planLater(right))) :: Nil
    +          execution.joins.CartesianProduct(planLater(left), planLater(right),
    +            getSmallSide(left, right))) :: Nil
    --- End diff --
    
    instead of passing a `BuildSide` to `CartesianProduct`, why not just change the parameters order according to the data size? like
    ```
    if (left < right) {
      CartesianProduct(left, right)
    } else {
      CartesianProduct(right, left)
    }
    ```


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