Remove mapSideCombine field from Aggregator.

Instead, the presence or absense of a ShuffleDependency's aggregator
will control whether map-side combining is performed.

4 files changed, 10 insertions, 7 deletions

diff --git a/core/src/main/scala/spark/Aggregator.scala b/core/src/main/scala/spark/Aggregator.scala
index 8d4f982413..df8ce9c054 100644
--- a/core/src/main/scala/spark/Aggregator.scala
+++ b/core/src/main/scala/spark/Aggregator.scala
@@ -9,15 +9,11 @@ import scala.collection.JavaConversions._
   * @param createCombiner function to create the initial value of the aggregation.
   * @param mergeValue function to merge a new value into the aggregation result.
   * @param mergeCombiners function to merge outputs from multiple mergeValue function.
-  * @param mapSideCombine whether to apply combiners on map partitions, also
-  *                       known as map-side aggregations. When set to false, 
-  *                       mergeCombiners function is not used.
   */
 case class Aggregator[K, V, C] (
     val createCombiner: V => C,
     val mergeValue: (C, V) => C,
-    val mergeCombiners: (C, C) => C,
-    val mapSideCombine: Boolean = true) {
+    val mergeCombiners: (C, C) => C) {
 
   def combineValuesByKey(iter: Iterator[(K, V)]) : Iterator[(K, C)] = {
     val combiners = new JHashMap[K, C]
diff --git a/core/src/main/scala/spark/Dependency.scala b/core/src/main/scala/spark/Dependency.scala
index 19a51dd5b8..5a67073ef4 100644
--- a/core/src/main/scala/spark/Dependency.scala
+++ b/core/src/main/scala/spark/Dependency.scala
@@ -22,7 +22,7 @@ abstract class NarrowDependency[T](rdd: RDD[T]) extends Dependency(rdd) {
  * Represents a dependency on the output of a shuffle stage.
  * @param shuffleId the shuffle id
  * @param rdd the parent RDD
- * @param aggregator optional aggregator; this allows for map-side combining
+ * @param aggregator optional aggregator; if provided, map-side combining will be performed
  * @param partitioner partitioner used to partition the shuffle output
  */
 class ShuffleDependency[K, V, C](
diff --git a/core/src/main/scala/spark/rdd/ShuffledRDD.scala b/core/src/main/scala/spark/rdd/ShuffledRDD.scala
index 04234491a6..8b1c29b065 100644
--- a/core/src/main/scala/spark/rdd/ShuffledRDD.scala
+++ b/core/src/main/scala/spark/rdd/ShuffledRDD.scala
@@ -14,6 +14,13 @@ private[spark] class ShuffledRDDSplit(val idx: Int) extends Split {
 
 /**
  * The resulting RDD from a shuffle (e.g. repartitioning of data).
+ * @param parent the parent RDD.
+ * @param aggregator if provided, this aggregator will be used to perform map-side combining.
+ * @param part the partitioner used to partition the RDD
+ * @tparam K the key class.
+ * @tparam V the value class.
+ * @tparam C if map side combiners are used, then this is the combiner type; otherwise,
+ *           this is the same as V.
  */
 class ShuffledRDD[K, V, C](
     @transient parent: RDD[(K, V)],
diff --git a/core/src/main/scala/spark/scheduler/ShuffleMapTask.scala b/core/src/main/scala/spark/scheduler/ShuffleMapTask.scala
index 86796d3677..c97be18844 100644
--- a/core/src/main/scala/spark/scheduler/ShuffleMapTask.scala
+++ b/core/src/main/scala/spark/scheduler/ShuffleMapTask.scala
@@ -114,7 +114,7 @@ private[spark] class ShuffleMapTask(
     val partitioner = dep.partitioner
 
     val bucketIterators =
-      if (dep.aggregator.isDefined && dep.aggregator.get.mapSideCombine) {
+      if (dep.aggregator.isDefined) {
         val aggregator = dep.aggregator.get.asInstanceOf[Aggregator[Any, Any, Any]]
         // Apply combiners (map-side aggregation) to the map output.
         val buckets = Array.tabulate(numOutputSplits)(_ => new JHashMap[Any, Any])