Github user markhamstra commented on a diff in the pull request:

    https://github.com/apache/spark/pull/1689#discussion_r15920203
  
    --- Diff: core/src/main/scala/org/apache/spark/Partitioner.scala ---
    @@ -113,8 +113,12 @@ class RangePartitioner[K : Ordering : ClassTag, V](
       private var ordering = implicitly[Ordering[K]]
     
       // An array of upper bounds for the first (partitions - 1) partitions
    -  private var rangeBounds: Array[K] = {
    -    if (partitions <= 1) {
    +  @volatile private var valRB: Array[K] = null
    --- End diff --
    
    It wouldn't surprise me if this performance figure varied with different 
combinations of hardware and Java version; but for at least one such 
combination, volatile reads are roughly 2-3x as costly as non-volatile reads as 
long as they are uncontended -- much more expensive when there are concurrent 
writes to contend with. http://brooker.co.za/blog/2012/09/10/volatile.html 


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