Add 'iterator' to reduce memory consumed by join

Author: zsxwing

core/src/main/scala/org/apache/spark/rdd/PairRDDFunctions.scala

@@ -480,7 +480,7 @@ class PairRDDFunctions[K, V](self: RDD[(K, V)])
    */
   def join[W](other: RDD[(K, W)], partitioner: Partitioner): RDD[(K, (V, W))] = {
     this.cogroup(other, partitioner).flatMapValues( pair =>
-      for (v <- pair._1; w <- pair._2) yield (v, w)
+      for (v <- pair._1.iterator; w <- pair._2.iterator) yield (v, w)
     )
   }
 
@@ -493,9 +493,9 @@ class PairRDDFunctions[K, V](self: RDD[(K, V)])
   def leftOuterJoin[W](other: RDD[(K, W)], partitioner: Partitioner): RDD[(K, (V, Option[W]))] = {
     this.cogroup(other, partitioner).flatMapValues { pair =>
       if (pair._2.isEmpty) {
-        pair._1.map(v => (v, None))
+        pair._1.iterator.map(v => (v, None): (V, Option[W]))
       } else {
-        for (v <- pair._1; w <- pair._2) yield (v, Some(w))
+        for (v <- pair._1.iterator; w <- pair._2.iterator) yield (v, Some(w))
       }
     }
   }
@@ -510,9 +510,9 @@ class PairRDDFunctions[K, V](self: RDD[(K, V)])
       : RDD[(K, (Option[V], W))] = {
     this.cogroup(other, partitioner).flatMapValues { pair =>
       if (pair._1.isEmpty) {
-        pair._2.map(w => (None, w))
+        pair._2.iterator.map(w => (None, w): (Option[V], W))
       } else {
-        for (v <- pair._1; w <- pair._2) yield (Some(v), w)
+        for (v <- pair._1.iterator; w <- pair._2.iterator) yield (Some(v), w)
       }
     }
   }
@@ -528,9 +528,9 @@ class PairRDDFunctions[K, V](self: RDD[(K, V)])
   def fullOuterJoin[W](other: RDD[(K, W)], partitioner: Partitioner)
       : RDD[(K, (Option[V], Option[W]))] = {
     this.cogroup(other, partitioner).flatMapValues {
-      case (vs, Seq()) => vs.map(v => (Some(v), None))
-      case (Seq(), ws) => ws.map(w => (None, Some(w)))
-      case (vs, ws) => for (v <- vs; w <- ws) yield (Some(v), Some(w))
+      case (vs, Seq()) => vs.iterator.map(v => (Some(v), None): (Option[V], Option[W]))
+      case (Seq(), ws) => ws.iterator.map(w => (None, Some(w)): (Option[V], Option[W]))
+      case (vs, ws) => for (v <- vs.iterator; w <- ws.iterator) yield (Some(v), Some(w))
     }
   }