Added mapSideCombine flag to CoGroupedRDD. Added unit test for

CoGroupedRDD.

core/src/main/scala/spark/rdd/CoGroupedRDD.scala

@@ -2,10 +2,11 @@ package spark.rdd
 
 import java.io.{ObjectOutputStream, IOException}
 import java.util.{HashMap => JHashMap}
+
 import scala.collection.JavaConversions
 import scala.collection.mutable.ArrayBuffer
 
-import spark.{Aggregator, Logging, Partitioner, RDD, SparkEnv, Partition, TaskContext}
+import spark.{Aggregator, Logging, Partition, Partitioner, RDD, SparkEnv, TaskContext}
 import spark.{Dependency, OneToOneDependency, ShuffleDependency}
 
 
@@ -28,7 +29,8 @@ private[spark] case class NarrowCoGroupSplitDep(
 private[spark] case class ShuffleCoGroupSplitDep(shuffleId: Int) extends CoGroupSplitDep
 
 private[spark]
-class CoGroupPartition(idx: Int, val deps: Seq[CoGroupSplitDep]) extends Partition with Serializable {
+class CoGroupPartition(idx: Int, val deps: Seq[CoGroupSplitDep])
+  extends Partition with Serializable {
   override val index: Int = idx
   override def hashCode(): Int = idx
 }
@@ -40,7 +42,19 @@ private[spark] class CoGroupAggregator
     { (b1, b2) => b1 ++ b2 })
   with Serializable
 
-class CoGroupedRDD[K](@transient var rdds: Seq[RDD[(K, _)]], part: Partitioner)
+
+/**
+ * A RDD that cogroups its parents. For each key k in parent RDDs, the resulting RDD contains a
+ * tuple with the list of values for that key.
+ *
+ * @param rdds parent RDDs.
+ * @param part partitioner used to partition the shuffle output.
+ * @param mapSideCombine flag indicating whether to merge values before shuffle step.
+ */
+class CoGroupedRDD[K](
+  @transient var rdds: Seq[RDD[(K, _)]],
+  part: Partitioner,
+  val mapSideCombine: Boolean = true)
   extends RDD[(K, Seq[Seq[_]])](rdds.head.context, Nil) {
 
   private val aggr = new CoGroupAggregator
@@ -52,8 +66,12 @@ class CoGroupedRDD[K](@transient var rdds: Seq[RDD[(K, _)]], part: Partitioner)
         new OneToOneDependency(rdd)
       } else {
         logInfo("Adding shuffle dependency with " + rdd)
-        val mapSideCombinedRDD = rdd.mapPartitions(aggr.combineValuesByKey(_), true)
-        new ShuffleDependency[Any, ArrayBuffer[Any]](mapSideCombinedRDD, part)
+        if (mapSideCombine) {
+          val mapSideCombinedRDD = rdd.mapPartitions(aggr.combineValuesByKey(_), true)
+          new ShuffleDependency[Any, ArrayBuffer[Any]](mapSideCombinedRDD, part)
+        } else {
+          new ShuffleDependency[Any, Any](rdd.asInstanceOf[RDD[(Any, Any)]], part)
+        }
       }
     }
   }
@@ -82,6 +100,7 @@ class CoGroupedRDD[K](@transient var rdds: Seq[RDD[(K, _)]], part: Partitioner)
     val numRdds = split.deps.size
     // e.g. for `(k, a) cogroup (k, b)`, K -> Seq(ArrayBuffer as, ArrayBuffer bs)
     val map = new JHashMap[K, Seq[ArrayBuffer[Any]]]
+
     def getSeq(k: K): Seq[ArrayBuffer[Any]] = {
       val seq = map.get(k)
       if (seq != null) {
@@ -92,6 +111,7 @@ class CoGroupedRDD[K](@transient var rdds: Seq[RDD[(K, _)]], part: Partitioner)
         seq
       }
     }
+
     for ((dep, depNum) <- split.deps.zipWithIndex) dep match {
       case NarrowCoGroupSplitDep(rdd, _, itsSplit) => {
         // Read them from the parent
@@ -102,9 +122,16 @@ class CoGroupedRDD[K](@transient var rdds: Seq[RDD[(K, _)]], part: Partitioner)
       case ShuffleCoGroupSplitDep(shuffleId) => {
         // Read map outputs of shuffle
         val fetcher = SparkEnv.get.shuffleFetcher
-        val fetchItr = fetcher.fetch[K, Seq[Any]](shuffleId, split.index, context.taskMetrics)
-        for ((k, vs) <- fetchItr) {
-          getSeq(k)(depNum) ++= vs
+        if (mapSideCombine) {
+          // With map side combine on, for each key, the shuffle fetcher returns a list of values.
+          fetcher.fetch[K, Seq[Any]](shuffleId, split.index, context.taskMetrics).foreach {
+            case (key, values) => getSeq(key)(depNum) ++= values
+          }
+        } else {
+          // With map side combine off, for each key the shuffle fetcher returns a single value.
+          fetcher.fetch[K, Any](shuffleId, split.index, context.taskMetrics).foreach {
+            case (key, value) => getSeq(key)(depNum) += value
+          }
         }
       }
     }

core/src/test/scala/spark/RDDSuite.scala

@@ -3,7 +3,7 @@ package spark
 import scala.collection.mutable.HashMap
 import org.scalatest.FunSuite
 import spark.SparkContext._
-import spark.rdd.{CoalescedRDD, PartitionPruningRDD}
+import spark.rdd.{CoalescedRDD, CoGroupedRDD, PartitionPruningRDD}
 
 class RDDSuite extends FunSuite with LocalSparkContext {
 
@@ -123,6 +123,36 @@ class RDDSuite extends FunSuite with LocalSparkContext {
     assert(rdd.collect().toList === List(1, 2, 3, 4))
   }
 
+  test("cogrouped RDDs") {
+    sc = new SparkContext("local", "test")
+    val rdd1 = sc.makeRDD(Array((1, "one"), (1, "another one"), (2, "two"), (3, "three")), 2)
+    val rdd2 = sc.makeRDD(Array((1, "one1"), (1, "another one1"), (2, "two1")), 2)
+
+    // Use cogroup function
+    val cogrouped = rdd1.cogroup(rdd2).collectAsMap()
+    assert(cogrouped(1) === (Seq("one", "another one"), Seq("one1", "another one1")))
+    assert(cogrouped(2) === (Seq("two"), Seq("two1")))
+    assert(cogrouped(3) === (Seq("three"), Seq()))
+
+    // Construct CoGroupedRDD directly, with map side combine enabled
+    val cogrouped1 = new CoGroupedRDD[Int](
+      Seq(rdd1.asInstanceOf[RDD[(Int, Any)]], rdd2.asInstanceOf[RDD[(Int, Any)]]),
+      new HashPartitioner(3),
+      true).collectAsMap()
+    assert(cogrouped1(1).toSeq === Seq(Seq("one", "another one"), Seq("one1", "another one1")))
+    assert(cogrouped1(2).toSeq === Seq(Seq("two"), Seq("two1")))
+    assert(cogrouped1(3).toSeq === Seq(Seq("three"), Seq()))
+
+    // Construct CoGroupedRDD directly, with map side combine disabled
+    val cogrouped2 = new CoGroupedRDD[Int](
+      Seq(rdd1.asInstanceOf[RDD[(Int, Any)]], rdd2.asInstanceOf[RDD[(Int, Any)]]),
+      new HashPartitioner(3),
+      false).collectAsMap()
+    assert(cogrouped2(1).toSeq === Seq(Seq("one", "another one"), Seq("one1", "another one1")))
+    assert(cogrouped2(2).toSeq === Seq(Seq("two"), Seq("two1")))
+    assert(cogrouped2(3).toSeq === Seq(Seq("three"), Seq()))
+  }
+
   test("coalesced RDDs") {
     sc = new SparkContext("local", "test")
     val data = sc.parallelize(1 to 10, 10)