Review comments

core/src/main/scala/org/apache/spark/SparkEnv.scala

@@ -252,10 +252,10 @@ object SparkEnv extends Logging {
 
     // Let the user specify short names for shuffle managers
     val shortShuffleMgrNames = Map(
-      "HASH" -> "org.apache.spark.shuffle.hash.HashShuffleManager",
-      "SORT" -> "org.apache.spark.shuffle.sort.SortShuffleManager")
-    val shuffleMgrName = conf.get("spark.shuffle.manager", "HASH")
-    val shuffleMgrClass = shortShuffleMgrNames.getOrElse(shuffleMgrName, shuffleMgrName)
+      "hash" -> "org.apache.spark.shuffle.hash.HashShuffleManager",
+      "sort" -> "org.apache.spark.shuffle.sort.SortShuffleManager")
+    val shuffleMgrName = conf.get("spark.shuffle.manager", "hash")
+    val shuffleMgrClass = shortShuffleMgrNames.getOrElse(shuffleMgrName.toLowerCase, shuffleMgrName)
     val shuffleManager = instantiateClass[ShuffleManager](shuffleMgrClass)
 
     val shuffleMemoryManager = new ShuffleMemoryManager(conf)

core/src/main/scala/org/apache/spark/shuffle/sort/SortShuffleWriter.scala

@@ -66,9 +66,9 @@ private[spark] class SortShuffleWriter[K, V, C](
         dep.aggregator, Some(dep.partitioner), dep.keyOrdering, dep.serializer)
       sorter.insertAll(records)
     } else {
-      // In this case we pass neither an aggregator nor an ordering to the sorter, because we
-      // don't care whether the keys get sorted in each partition; that will be done on the
-      // reduce side if the operation being run is sortByKey.
+      // In this case we pass neither an aggregator nor an ordering to the sorter, because we don't
+      // care whether the keys get sorted in each partition; that will be done on the reduce side
+      // if the operation being run is sortByKey.
       sorter = new ExternalSorter[K, V, V](
         None, Some(dep.partitioner), None, dep.serializer)
       sorter.insertAll(records)

core/src/main/scala/org/apache/spark/util/collection/ExternalSorter.scala

@@ -137,10 +137,10 @@ private[spark] class ExternalSorter[K, V, C](
   // spilled files, which would happen with the normal code path. The downside is having multiple
   // files open at a time and thus more memory allocated to buffers.
   private val bypassMergeThreshold = conf.getInt("spark.shuffle.sort.bypassMergeThreshold", 200)
-  private[collection] val bypassMergeSort =            // private[collection] for unit tests
+  private val bypassMergeSort =
     (numPartitions <= bypassMergeThreshold && aggregator.isEmpty && ordering.isEmpty)
 
-  // Array of file writers for each partition, used if bypassMergeSort is true
+  // Array of file writers for each partition, used if bypassMergeSort is true and we've spilled
   private var partitionWriters: Array[BlockObjectWriter] = null
 
   // A comparator for keys K that orders them within a partition to allow aggregation or sorting.

core/src/test/scala/org/apache/spark/util/collection/ExternalSorterSuite.scala

@@ -19,12 +19,12 @@ package org.apache.spark.util.collection
 
 import scala.collection.mutable.ArrayBuffer
 
-import org.scalatest.FunSuite
+import org.scalatest.{PrivateMethodTester, FunSuite}
 
 import org.apache.spark._
 import org.apache.spark.SparkContext._
 
-class ExternalSorterSuite extends FunSuite with LocalSparkContext {
+class ExternalSorterSuite extends FunSuite with LocalSparkContext with PrivateMethodTester {
   private def createSparkConf(loadDefaults: Boolean): SparkConf = {
     val conf = new SparkConf(loadDefaults)
     // Make the Java serializer write a reset instruction (TC_RESET) after each object to test
@@ -36,6 +36,16 @@ class ExternalSorterSuite extends FunSuite with LocalSparkContext {
     conf
   }
 
+  private def assertBypassedMergeSort(sorter: ExternalSorter[_, _, _]): Unit = {
+    val bypassMergeSort = PrivateMethod[Boolean]('bypassMergeSort)
+    assert(sorter.invokePrivate(bypassMergeSort()), "sorter did not bypass merge-sort")
+  }
+
+  private def assertDidNotBypassMergeSort(sorter: ExternalSorter[_, _, _]): Unit = {
+    val bypassMergeSort = PrivateMethod[Boolean]('bypassMergeSort)
+    assert(!sorter.invokePrivate(bypassMergeSort()), "sorter bypassed merge-sort")
+  }
+
   test("empty data stream") {
     val conf = new SparkConf(false)
     conf.set("spark.shuffle.memoryFraction", "0.001")
@@ -123,7 +133,7 @@ class ExternalSorterSuite extends FunSuite with LocalSparkContext {
 
     val sorter = new ExternalSorter[Int, Int, Int](
       None, Some(new HashPartitioner(7)), Some(ord), None)
-    assert(!sorter.bypassMergeSort, "sorter bypassed merge-sort")
+    assertDidNotBypassMergeSort(sorter)
     sorter.insertAll(elements)
     assert(sc.env.blockManager.diskBlockManager.getAllFiles().length > 0) // Make sure it spilled
     val iter = sorter.partitionedIterator.map(p => (p._1, p._2.toList))
@@ -147,7 +157,7 @@ class ExternalSorterSuite extends FunSuite with LocalSparkContext {
 
     val sorter = new ExternalSorter[Int, Int, Int](
       None, Some(new HashPartitioner(7)), None, None)
-    assert(sorter.bypassMergeSort, "sorter did not bypass merge-sort")
+    assertBypassedMergeSort(sorter)
     sorter.insertAll(elements)
     assert(sc.env.blockManager.diskBlockManager.getAllFiles().length > 0) // Make sure it spilled
     val iter = sorter.partitionedIterator.map(p => (p._1, p._2.toList))
@@ -314,15 +324,15 @@ class ExternalSorterSuite extends FunSuite with LocalSparkContext {
 
     val sorter = new ExternalSorter[Int, Int, Int](
       None, Some(new HashPartitioner(3)), Some(ord), None)
-    assert(!sorter.bypassMergeSort, "sorter bypassed merge-sort")
+    assertDidNotBypassMergeSort(sorter)
     sorter.insertAll((0 until 100000).iterator.map(i => (i, i)))
     assert(diskBlockManager.getAllFiles().length > 0)
     sorter.stop()
     assert(diskBlockManager.getAllBlocks().length === 0)
 
     val sorter2 = new ExternalSorter[Int, Int, Int](
       None, Some(new HashPartitioner(3)), Some(ord), None)
-    assert(!sorter2.bypassMergeSort, "sorter bypassed merge-sort")
+    assertDidNotBypassMergeSort(sorter2)
     sorter2.insertAll((0 until 100000).iterator.map(i => (i, i)))
     assert(diskBlockManager.getAllFiles().length > 0)
     assert(sorter2.iterator.toSet === (0 until 100000).map(i => (i, i)).toSet)
@@ -338,14 +348,14 @@ class ExternalSorterSuite extends FunSuite with LocalSparkContext {
     val diskBlockManager = SparkEnv.get.blockManager.diskBlockManager
 
     val sorter = new ExternalSorter[Int, Int, Int](None, Some(new HashPartitioner(3)), None, None)
-    assert(sorter.bypassMergeSort, "sorter did not bypass merge-sort")
+    assertBypassedMergeSort(sorter)
     sorter.insertAll((0 until 100000).iterator.map(i => (i, i)))
     assert(diskBlockManager.getAllFiles().length > 0)
     sorter.stop()
     assert(diskBlockManager.getAllBlocks().length === 0)
 
     val sorter2 = new ExternalSorter[Int, Int, Int](None, Some(new HashPartitioner(3)), None, None)
-    assert(sorter2.bypassMergeSort, "sorter did not bypass merge-sort")
+    assertBypassedMergeSort(sorter2)
     sorter2.insertAll((0 until 100000).iterator.map(i => (i, i)))
     assert(diskBlockManager.getAllFiles().length > 0)
     assert(sorter2.iterator.toSet === (0 until 100000).map(i => (i, i)).toSet)
@@ -364,7 +374,7 @@ class ExternalSorterSuite extends FunSuite with LocalSparkContext {
 
     val sorter = new ExternalSorter[Int, Int, Int](
       None, Some(new HashPartitioner(3)), Some(ord), None)
-    assert(!sorter.bypassMergeSort, "sorter bypassed merge-sort")
+    assertDidNotBypassMergeSort(sorter)
     intercept[SparkException] {
       sorter.insertAll((0 until 100000).iterator.map(i => {
         if (i == 99990) {
@@ -386,7 +396,7 @@ class ExternalSorterSuite extends FunSuite with LocalSparkContext {
     val diskBlockManager = SparkEnv.get.blockManager.diskBlockManager
 
     val sorter = new ExternalSorter[Int, Int, Int](None, Some(new HashPartitioner(3)), None, None)
-    assert(sorter.bypassMergeSort, "sorter did not bypass merge-sort")
+    assertBypassedMergeSort(sorter)
     intercept[SparkException] {
       sorter.insertAll((0 until 100000).iterator.map(i => {
         if (i == 99990) {
@@ -681,20 +691,20 @@ class ExternalSorterSuite extends FunSuite with LocalSparkContext {
 
     val sorter1 = new ExternalSorter[Int, Int, Int](
       None, Some(new HashPartitioner(FEW_PARTITIONS)), None, None)
-    assert(sorter1.bypassMergeSort, "sorter did not bypass merge-sort")
+    assertBypassedMergeSort(sorter1)
 
     val sorter2 = new ExternalSorter[Int, Int, Int](
       None, Some(new HashPartitioner(MANY_PARTITIONS)), None, None)
-    assert(!sorter2.bypassMergeSort, "sorter bypassed merge-sort")
+    assertDidNotBypassMergeSort(sorter2)
 
     // Sorters with an ordering or aggregator: should not bypass even if they have few partitions
 
     val sorter3 = new ExternalSorter[Int, Int, Int](
       None, Some(new HashPartitioner(FEW_PARTITIONS)), Some(ord), None)
-    assert(!sorter3.bypassMergeSort, "sorter bypassed merge-sort")
+    assertDidNotBypassMergeSort(sorter3)
 
     val sorter4 = new ExternalSorter[Int, Int, Int](
       Some(agg), Some(new HashPartitioner(FEW_PARTITIONS)), None, None)
-    assert(!sorter4.bypassMergeSort, "sorter bypassed merge-sort")
+    assertDidNotBypassMergeSort(sorter4)
   }
 }