[GitHub] [spark] srowen commented on a change in pull request #23986: [SPARK-27070] Fix performance bug in DefaultPartitionCoalescer

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srowen commented on a change in pull request #23986: [SPARK-27070] Fix performance bug in DefaultPartitionCoalescer
URL: https://github.com/apache/spark/pull/23986#discussion_r262932060
 
 

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 File path: core/src/main/scala/org/apache/spark/rdd/CoalescedRDD.scala
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 @@ -156,9 +156,11 @@ private[spark] class CoalescedRDD[T: ClassTag](
 
 private class DefaultPartitionCoalescer(val balanceSlack: Double = 0.10)
   extends PartitionCoalescer {
-  def compare(o1: PartitionGroup, o2: PartitionGroup): Boolean = o1.numPartitions < o2.numPartitions
-  def compare(o1: Option[PartitionGroup], o2: Option[PartitionGroup]): Boolean =
-    if (o1 == None) false else if (o2 == None) true else compare(o1.get, o2.get)
+
+  implicit val partitionGroupOrdering: Ordering[PartitionGroup]
+  = (o1: PartitionGroup, o2: PartitionGroup)
+  => o1.numPartitions - o2.numPartitions
 
 Review comment:
   The indent is off here. Returning the result of a subtraction in compare can overflow, though I don't think it can happen in practice here. Still, see below, I think we can just remove this.

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