diff --git a/core/src/main/scala/org/apache/spark/rdd/OrderedRDDFunctions.scala b/core/src/main/scala/org/apache/spark/rdd/OrderedRDDFunctions.scala
index 6a3f69844428..8147f7bc382f 100644
--- a/core/src/main/scala/org/apache/spark/rdd/OrderedRDDFunctions.scala
+++ b/core/src/main/scala/org/apache/spark/rdd/OrderedRDDFunctions.scala
@@ -58,13 +58,10 @@ class OrderedRDDFunctions[K : Ordering : ClassTag,
   def sortByKey(ascending: Boolean = true, numPartitions: Int = self.partitions.size): RDD[P] = {
     val part = new RangePartitioner(numPartitions, self, ascending)
     val shuffled = new ShuffledRDD[K, V, P](self, part)
-    shuffled.mapPartitions(iter => {
-      val buf = iter.toArray
-      if (ascending) {
-        buf.sortWith((x, y) => ordering.lt(x._1, y._1)).iterator
-      } else {
-        buf.sortWith((x, y) => ordering.gt(x._1, y._1)).iterator
-      }
-    }, preservesPartitioning = true)
+    if (ascending) {
+      shuffled.sortPartitions((x, y) => ordering.lt(x._1, y._1))
+    } else {
+      shuffled.sortPartitions((x, y) => ordering.gt(x._1, y._1))
+    }
   }
 }
diff --git a/core/src/main/scala/org/apache/spark/rdd/RDD.scala b/core/src/main/scala/org/apache/spark/rdd/RDD.scala
index 446f369c9ea1..e402cea5d062 100644
--- a/core/src/main/scala/org/apache/spark/rdd/RDD.scala
+++ b/core/src/main/scala/org/apache/spark/rdd/RDD.scala
@@ -280,6 +280,11 @@ abstract class RDD[T: ClassTag](
    */
   def filter(f: T => Boolean): RDD[T] = new FilteredRDD(this, sc.clean(f))
 
+  /**
+   * Return a new RDD containing sorted partitions in this RDD.
+   */
+  def sortPartitions(lt: (T, T) => Boolean): RDD[T] = new SortedPartitionsRDD(this, sc.clean(lt))
+
   /**
    * Return a new RDD containing the distinct elements in this RDD.
    */
diff --git a/core/src/main/scala/org/apache/spark/rdd/SortedParitionsRDD.scala b/core/src/main/scala/org/apache/spark/rdd/SortedParitionsRDD.scala
new file mode 100644
index 000000000000..9a530e10955a
--- /dev/null
+++ b/core/src/main/scala/org/apache/spark/rdd/SortedParitionsRDD.scala
@@ -0,0 +1,337 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.rdd
+
+import scala.reflect.ClassTag
+import scala.collection.mutable.ArrayBuffer
+import java.io.{InputStream, BufferedInputStream, FileInputStream, File, Serializable, EOFException}
+import org.apache.spark.{Partition, TaskContext}
+import org.apache.spark.{Logging, SparkEnv}
+import org.apache.spark.serializer.Serializer
+import org.apache.spark.storage.{BlockId, BlockManager}
+import org.apache.spark.util.SizeEstimator
+
+/**
+ * An RDD that sorts each of it's partitions independently.
+ * 
+ * If partitions are too large to fit in memory, they are externally sorted.
+ * 
+ * Two parameters control the memory threshold for external sort:
+ *
+ *   `spark.shuffle.memoryFraction` specifies the collective amount of memory used for storing
+ *   sub lists as a fraction of the executor's total memory. Since each concurrently running
+ *   task maintains one map, the actual threshold for each map is this quantity divided by the
+ *   number of running tasks.
+ *
+ *   `spark.shuffle.safetyFraction` specifies an additional margin of safety as a fraction of
+ *   this threshold, in case sub list size estimation is not sufficiently accurate.
+ */
+private[spark] class SortedPartitionsRDD[T: ClassTag](
+    prev: RDD[T],
+    lt: (T, T) => Boolean)
+  extends RDD[T](prev) {
+
+  override def getPartitions: Array[Partition] = firstParent[T].partitions
+
+  // Since sorting partitions cannot change a partition's keys
+  override val partitioner = prev.partitioner
+
+  override def compute(split: Partition, context: TaskContext) = {
+    new SortedIterator(firstParent[T].iterator(split, context), lt)
+  }
+}
+
+/**
+ * An iterator that sorts a supplied iterator, either in-memory or externally.
+ */
+private[spark] class SortedIterator[T](iter: Iterator[T], lt: (T, T) => Boolean)
+    extends Iterator[T] with Logging {
+  private val sparkConf = SparkEnv.get.conf
+  // Collective memory threshold shared across all running tasks
+  private val maxMemoryThreshold = {
+    val memoryFraction = sparkConf.getDouble("spark.shuffle.memoryFraction", 0.3)
+    val safetyFraction = sparkConf.getDouble("spark.shuffle.safetyFraction", 0.8)
+    (Runtime.getRuntime.maxMemory * memoryFraction * safetyFraction).toLong
+  }
+
+  // Number of list elements before tracking memory usage
+  private val trackMemoryThreshold = 1000
+
+  private val sorted = doSort()
+  
+  def hasNext : Boolean = {
+    sorted.hasNext
+  }
+  
+  def next : T = {
+    sorted.next
+  }
+  
+  /**
+   * Sort the incoming iterator.
+   * Any input that cannot fit in memory is split into sorted sub-lists and spilled to disk.
+   * Any spilled sub-lists are merge sorted and written back to disk.
+   */
+  private def doSort() : Iterator[T] = {
+    val subLists = new ArrayBuffer[Iterator[T]]()
+
+    // keep the first sub-list in memory
+    subLists += nextSubList
+
+    while (iter.hasNext) {
+      // spill remaining sub-lists to disk
+      var diskBuffer = new DiskBuffer[T]()
+      diskBuffer ++= nextSubList
+      subLists += diskBuffer.iterator
+    }
+    logInfo("Merge sorting one in-memory list with %d external list(s)".format(subLists.size - 1))
+
+    merge(subLists)
+  }
+
+  /**
+   * Gets a sorted sub-list that can fit in memory.
+   */
+  private def nextSubList() : Iterator[T] = {
+    var subList = new SizeTrackingArrayBuffer[T](1000)
+    while (fitsInMemory(subList) && iter.hasNext) {
+      subList += iter.next
+    }
+    return subList.sortWith(lt).iterator
+  }
+
+  /**
+   * Determines if a given list can fit in memory.
+   * This algorithm is similar to that found in ExternalAppendOnlyMap.
+   */
+  private def fitsInMemory(list : SizeTrackingArrayBuffer[T]) : Boolean = {
+    if (list.size > trackMemoryThreshold && list.atNextSampleSize) {
+      val listSize = list.estimateSize()
+      val shuffleMemoryMap = SparkEnv.get.shuffleMemoryMap
+
+      // Atomically check whether there is sufficient memory in the global pool for
+      // this map to grow and, if possible, allocate the required amount
+      shuffleMemoryMap.synchronized {
+        val threadId = Thread.currentThread().getId
+        val previouslyOccupiedMemory = shuffleMemoryMap.get(threadId)
+        val availableMemory = maxMemoryThreshold -
+          (shuffleMemoryMap.values.sum - previouslyOccupiedMemory.getOrElse(0L))
+
+        // Assume list growth factor is 2x
+        if (availableMemory > listSize * 2) {
+          shuffleMemoryMap(threadId) = listSize * 2
+        } else {
+          shuffleMemoryMap(threadId) = 0
+          return false
+        }
+      }
+    }
+    return true
+  }
+
+  /**
+   * Merge-sort a list of iterators, which might be in memory or disk.
+   * Returns a sorted iterator.
+   */
+  private def merge(list : ArrayBuffer[Iterator[T]]) : Iterator[T] = {
+    if (list.size == 1) {
+      return list(0)
+    }
+    if (list.size == 2) {
+      return doMerge(list(0), list(1))
+    }
+    val mid = list.size >> 1
+    val left = merge(list.slice(0, mid))
+    val right = merge(list.slice(mid, list.size))
+    doMerge(left, right)
+  }
+
+  /**
+   * Merge two iterators, returning a sorted iterator.
+   */
+  private def doMerge(it1 : Iterator[T], it2 : Iterator[T]) : Iterator[T] = {
+    var array = new DiskBuffer[T]()
+    if (!it1.hasNext) {
+      array ++= it2
+      return array.iterator
+    }
+    if (!it2.hasNext) {
+      array ++= it1
+      return array.iterator
+    }
+    var t1 = it1.next
+    var t2 = it2.next
+    while (true) {
+      if (lt(t1, t2)) {
+        array += t1
+        if (it1.hasNext) {
+          t1 = it1.next
+        } else {
+          array += t2
+          array ++= it2
+          return array.iterator
+        }
+      } else {
+        array += t2
+        if (it2.hasNext) {
+          t2 = it2.next
+        } else {
+          array += t1
+          array ++= it1
+          return array.iterator
+        }
+      }
+    }
+    array.iterator
+  }
+}
+
+/**
+ * A buffer similar to ArrayBuffer that can estimate it's size in bytes.
+ */
+private class SizeTrackingArrayBuffer[T](initialSize : Int) {
+  private var array = new ArrayBuffer[T](initialSize)
+  private var averageSize : Double = 0.0
+  private var nextSampleNum : Int = 1
+
+  def +=(elem: T): this.type = {
+    array += elem
+    updateAverage
+    this
+  }
+
+  def ++=(xs: TraversableOnce[T]): this.type = {
+    array ++= xs
+    updateAverage
+    this
+  }
+
+  def size : Int = {
+    array.size
+  }
+
+  def sortWith(lt: (T, T) => Boolean): this.type = {
+    array = array.sortWith(lt)
+    this
+  }
+
+  def iterator : Iterator[T] = {
+    array.iterator
+  }
+
+  def atNextSampleSize : Boolean = {
+    array.size >= nextSampleNum
+  }
+
+  def updateAverage = {
+    if (array.size >= nextSampleNum) {
+      averageSize = SizeEstimator.estimate(array)
+      averageSize /= array.size
+      nextSampleNum <<= 1
+      assert(nextSampleNum < 0x40000000)
+    }
+  }
+
+  def estimateSize(): Long = {
+    (array.size * averageSize).toLong
+  }
+}
+
+/**
+ * A buffer similar to ArrayBuffer, but stored on disk.
+ */
+private class DiskBuffer[T] {
+  private val serializer = SparkEnv.get.serializer
+  private val blockManager = SparkEnv.get.blockManager
+  private val diskBlockManager = blockManager.diskBlockManager
+  private val sparkConf = SparkEnv.get.conf
+  private val fileBufferSize = sparkConf.getInt("spark.shuffle.file.buffer.kb", 100) * 1024
+
+  val (blockId, file) = diskBlockManager.createTempBlock()
+  var writer = blockManager.getDiskWriter(blockId, file, serializer, fileBufferSize)
+  var numObjects : Int = 0
+
+  def +=(elem: T): this.type = {
+    numObjects += 1
+    writer.write(elem)
+    this
+  }
+
+  def ++=(xs: TraversableOnce[T]): this.type = {
+    xs.foreach({ numObjects += 1; writer.write(_) })
+    this
+  }
+
+  def iterator : Iterator[T] = {
+    writer.close
+    val fileBufferSize = sparkConf.getInt("spark.shuffle.file.buffer.kb", 100) * 1024
+    new DiskBufferIterator(file, blockId, serializer, fileBufferSize)
+  }
+}
+
+/**
+ * An iterator for DiskBuffer
+ */
+private class DiskBufferIterator[T](file: File, blockId: BlockId, serializer: Serializer,
+    fileBufferSize : Int) extends Iterator[T] {
+  private val fileStream = new FileInputStream(file)
+  private val bufferedStream = new BufferedInputStream(fileStream, fileBufferSize)
+  private var compressedStream =
+    SparkEnv.get.blockManager.wrapForCompression(blockId, bufferedStream)
+  private var deserializeStream = serializer.newInstance.deserializeStream(compressedStream)
+  private var nextItem = None : Option[T]
+  
+  def hasNext : Boolean = {
+    nextItem match {
+      case Some(item) => true
+      case None => nextItem = doNext()
+    }
+    nextItem match {
+      case Some(item) => true
+      case None => false
+    }
+  }
+  
+  def next() : T = {
+    nextItem match {
+      case Some(item) =>
+        nextItem = None
+        item
+      case None =>
+        doNext match {
+          case Some(item) => item
+          case None => throw new NoSuchElementException
+        }
+    }
+  }
+
+  private def doNext() : Option[T] = {
+    try {
+      Some(deserializeStream.readObject().asInstanceOf[T])
+    } catch {
+      case e: EOFException =>
+        cleanup
+        None
+    }
+  }
+
+  private def cleanup() = {
+    deserializeStream.close()
+    file.delete()
+  }
+}
diff --git a/core/src/test/scala/org/apache/spark/rdd/SortingSuite.scala b/core/src/test/scala/org/apache/spark/rdd/SortingSuite.scala
index 656917628f7a..6c52c0bc5b34 100644
--- a/core/src/test/scala/org/apache/spark/rdd/SortingSuite.scala
+++ b/core/src/test/scala/org/apache/spark/rdd/SortingSuite.scala
@@ -120,5 +120,15 @@ class SortingSuite extends FunSuite with SharedSparkContext with Matchers with L
     partitions(1).last should be > partitions(2).head
     partitions(2).last should be > partitions(3).head
   }
-}
 
+  test("sortPartitions") {
+    val rand = new scala.util.Random()
+    val array = Array.fill(10) { (rand.nextInt()) }
+    val pairs = sc.parallelize(array, 2)
+    val sorted = pairs.sortPartitions((x, y) => x < y)
+    assert(sorted.partitions.size === 2)
+    val partitions = sorted.collectPartitions()
+    assert(partitions(0) === partitions(0).sortWith((x, y) => x < y))
+    assert(partitions(1) === partitions(1).sortWith((x, y) => x < y))
+  }
+}