[SPARK-15958] Make initial buffer size for the Sorter configurable

## What changes were proposed in this pull request?

Currently the initial buffer size in the sorter is hard coded inside the code and is too small for large workload. As a result, the sorter spends significant time expanding the buffer size and copying the data. It would be useful to have it configurable.

## How was this patch tested?

Tested by running a job on the cluster.

Author: Sital Kedia <skedia@fb.com>

Closes #13699 from sitalkedia/config_sort_buffer_upstream.

2 files changed, 7 insertions, 4 deletions

diff --git a/core/src/main/java/org/apache/spark/shuffle/sort/UnsafeShuffleWriter.java b/core/src/main/java/org/apache/spark/shuffle/sort/UnsafeShuffleWriter.java
index daa63d47e6..05fa04c44d 100644
--- a/core/src/main/java/org/apache/spark/shuffle/sort/UnsafeShuffleWriter.java
+++ b/core/src/main/java/org/apache/spark/shuffle/sort/UnsafeShuffleWriter.java
@@ -61,7 +61,7 @@ public class UnsafeShuffleWriter<K, V> extends ShuffleWriter<K, V> {
   private static final ClassTag<Object> OBJECT_CLASS_TAG = ClassTag$.MODULE$.Object();
 
   @VisibleForTesting
-  static final int INITIAL_SORT_BUFFER_SIZE = 4096;
+  static final int DEFAULT_INITIAL_SORT_BUFFER_SIZE = 4096;
 
   private final BlockManager blockManager;
   private final IndexShuffleBlockResolver shuffleBlockResolver;
@@ -74,6 +74,7 @@ public class UnsafeShuffleWriter<K, V> extends ShuffleWriter<K, V> {
   private final TaskContext taskContext;
   private final SparkConf sparkConf;
   private final boolean transferToEnabled;
+  private final int initialSortBufferSize;
 
   @Nullable private MapStatus mapStatus;
   @Nullable private ShuffleExternalSorter sorter;
@@ -122,6 +123,8 @@ public class UnsafeShuffleWriter<K, V> extends ShuffleWriter<K, V> {
     this.taskContext = taskContext;
     this.sparkConf = sparkConf;
     this.transferToEnabled = sparkConf.getBoolean("spark.file.transferTo", true);
+    this.initialSortBufferSize = sparkConf.getInt("spark.shuffle.sort.initialBufferSize",
+                                                  DEFAULT_INITIAL_SORT_BUFFER_SIZE);
     open();
   }
 
@@ -187,7 +190,7 @@ public class UnsafeShuffleWriter<K, V> extends ShuffleWriter<K, V> {
       memoryManager,
       blockManager,
       taskContext,
-      INITIAL_SORT_BUFFER_SIZE,
+      initialSortBufferSize,
       partitioner.numPartitions(),
       sparkConf,
       writeMetrics);
diff --git a/core/src/test/java/org/apache/spark/shuffle/sort/UnsafeShuffleWriterSuite.java b/core/src/test/java/org/apache/spark/shuffle/sort/UnsafeShuffleWriterSuite.java
index 7dd61f85ab..daeb4675ea 100644
--- a/core/src/test/java/org/apache/spark/shuffle/sort/UnsafeShuffleWriterSuite.java
+++ b/core/src/test/java/org/apache/spark/shuffle/sort/UnsafeShuffleWriterSuite.java
@@ -413,10 +413,10 @@ public class UnsafeShuffleWriterSuite {
   }
 
   private void writeEnoughRecordsToTriggerSortBufferExpansionAndSpill() throws Exception {
-    memoryManager.limit(UnsafeShuffleWriter.INITIAL_SORT_BUFFER_SIZE * 16);
+    memoryManager.limit(UnsafeShuffleWriter.DEFAULT_INITIAL_SORT_BUFFER_SIZE * 16);
     final UnsafeShuffleWriter<Object, Object> writer = createWriter(false);
     final ArrayList<Product2<Object, Object>> dataToWrite = new ArrayList<>();
-    for (int i = 0; i < UnsafeShuffleWriter.INITIAL_SORT_BUFFER_SIZE + 1; i++) {
+    for (int i = 0; i < UnsafeShuffleWriter.DEFAULT_INITIAL_SORT_BUFFER_SIZE + 1; i++) {
       dataToWrite.add(new Tuple2<Object, Object>(i, i));
     }
     writer.write(dataToWrite.iterator());