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From hvanhovell <...@git.apache.org>
Subject [GitHub] spark pull request #15238: [SPARK-17653][SQL] Remove unnecessary distincts i...
Date Tue, 27 Sep 2016 17:49:57 GMT
Github user hvanhovell commented on a diff in the pull request:

    https://github.com/apache/spark/pull/15238#discussion_r80753108
  
    --- Diff: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/planning/patterns.scala
---
    @@ -191,25 +191,34 @@ object ExtractFiltersAndInnerJoins extends PredicateHelper {
     
     /**
      * A pattern that collects all adjacent unions and returns their children as a Seq.
    + * If the top union is wrapped in a [[Distinct]], then the [[Distinct]] in the adjacent
unions, if
    + * any, will be eliminated.
      */
     object Unions {
    -  def unapply(plan: LogicalPlan): Option[Seq[LogicalPlan]] = plan match {
    -    case u: Union => Some(collectUnionChildren(mutable.Stack(u), Seq.empty[LogicalPlan]))
    +  def unapply(plan: LogicalPlan): Option[(Seq[LogicalPlan], Boolean)] = plan match {
    +    case u: Union =>
    +      Some(collectUnionChildren(mutable.Stack(u), Seq.empty[LogicalPlan], false), false)
    +    case Distinct(u: Union) =>
    +      Some(collectUnionChildren(mutable.Stack(u), Seq.empty[LogicalPlan], true), true)
         case _ => None
       }
     
       // Doing a depth-first tree traversal to combine all the union children.
       @tailrec
       private def collectUnionChildren(
           plans: mutable.Stack[LogicalPlan],
    -      children: Seq[LogicalPlan]): Seq[LogicalPlan] = {
    +      children: Seq[LogicalPlan],
    +      dedupDistinct: Boolean): Seq[LogicalPlan] = {
    --- End diff --
    
    Why is this method so complicated? It seems that we can do without the stack. A stack
only makes sense if you do not want use recursion (you can use a while loop instead). This
comment has nothing to do with this PR, but with the code as it was to begin with. Could you
fix it anyway?
    
    cc @gatorsmile as well


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