Merge -r 679878:679879 from trunk to branch-0.18 to fix HADOOP-3827

git-svn-id: https://svn.apache.org/repos/asf/hadoop/core/branches/branch-0.18@680822 13f79535-47bb-0310-9956-ffa450edef68

CHANGES.txt

@@ -770,6 +770,8 @@ Release 0.18.0 - Unreleased
 
     HADOOP-3724. Fixes two problems related to storing and recovering lease
     in the fsimage. (dhruba)
+    
+    HADOOP-3827.  Fixed compression of empty map-outputs. (acmurthy) 
 
 Release 0.17.2 - Unreleased
 

src/mapred/org/apache/hadoop/mapred/MapTask.java

@@ -1008,7 +1008,7 @@ class MapTask extends Task {
         for (int i = 0; i < partitions; i++) {
           long segmentStart = finalOut.getPos();
           Writer<K, V> writer = new Writer<K, V>(job, finalOut, 
-                                                 keyClass, valClass, null);
+                                                 keyClass, valClass, codec);
           writer.close();
           writeIndexRecord(finalIndexOut, finalOut, segmentStart, writer);
         }

src/test/org/apache/hadoop/mapred/TestCompressedEmptyMapOutputs.java

@@ -0,0 +1,123 @@
+/**
+ * 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.hadoop.mapred;
+
+import java.io.IOException;
+
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.examples.RandomWriter;
+import org.apache.hadoop.fs.FileSystem;
+import org.apache.hadoop.fs.Path;
+import org.apache.hadoop.hdfs.MiniDFSCluster;
+import org.apache.hadoop.io.BytesWritable;
+import org.apache.hadoop.mapred.lib.IdentityReducer;
+import org.apache.hadoop.util.ToolRunner;
+
+import junit.framework.TestCase;
+
+/**
+ * A JUnit test to test the Map-Reduce framework's sort in presence of 
+ * null intermediate map-outputs, when compression is enabled for intermediate
+ * map-outputs. 
+ */
+public class TestCompressedEmptyMapOutputs extends TestCase {
+  // Input/Output paths for sort
+  private static final Path SORT_INPUT_PATH = new Path("/sort/input");
+  private static final Path SORT_OUTPUT_PATH = new Path("/sort/output");
+
+  // Knobs to control randomwriter; and hence sort
+  private static final int NUM_HADOOP_SLAVES = 3;
+  private static final int RW_BYTES_PER_MAP = 50000;
+  private static final int RW_MAPS_PER_HOST = 5;
+  
+  private static void runRandomWriter(JobConf job, Path sortInput) 
+  throws Exception {
+    // Scale down the default settings for RandomWriter for the test-case
+    // Generates NUM_HADOOP_SLAVES * RW_MAPS_PER_HOST * RW_BYTES_PER_MAP -> 1MB
+    job.setInt("test.randomwrite.bytes_per_map", RW_BYTES_PER_MAP);
+    job.setInt("test.randomwriter.maps_per_host", RW_MAPS_PER_HOST);
+    String[] rwArgs = {sortInput.toString()};
+    
+    // Run RandomWriter
+    assertEquals(ToolRunner.run(job, new RandomWriter(), rwArgs), 0);
+  }
+
+
+  static class SinkMapper<K, V>
+  extends MapReduceBase implements Mapper<K, V, K, V> {
+
+    public void map(K key, V val,
+        OutputCollector<K, V> output, Reporter reporter)
+    throws IOException {
+      // Don't output anything!
+      if (false) output.collect(key, val);
+    }
+  }
+
+  private static void runSort(JobConf jobConf, Path sortInput, Path sortOutput) 
+  throws Exception {
+    // Set up the job
+    jobConf.setJobName("null-sorter");
+    
+    jobConf.setMapperClass(SinkMapper.class);
+    jobConf.setReducerClass(IdentityReducer.class);
+
+    jobConf.setNumReduceTasks(2);
+
+    jobConf.setInputFormat(SequenceFileInputFormat.class);
+    jobConf.setOutputFormat(SequenceFileOutputFormat.class);
+
+    jobConf.setOutputKeyClass(BytesWritable.class);
+    jobConf.setOutputValueClass(BytesWritable.class);
+    
+    FileInputFormat.setInputPaths(jobConf, sortInput);
+    FileOutputFormat.setOutputPath(jobConf, sortOutput);
+
+    // Compress the intermediate map-outputs!
+    jobConf.setCompressMapOutput(true);
+
+    // Run the job
+    JobClient.runJob(jobConf);
+  }
+  
+  public void testMapReduceSortWithCompressedEmptyMapOutputs() 
+  throws Exception {
+    MiniDFSCluster dfs = null;
+    MiniMRCluster mr = null;
+    FileSystem fileSys = null;
+    try {
+      Configuration conf = new Configuration();
+
+      // Start the mini-MR and mini-DFS clusters
+      dfs = new MiniDFSCluster(conf, NUM_HADOOP_SLAVES, true, null);
+      fileSys = dfs.getFileSystem();
+      mr = new MiniMRCluster(NUM_HADOOP_SLAVES, fileSys.getUri().toString(), 1);
+
+      // Run randomwriter to generate input for 'sort'
+      runRandomWriter(mr.createJobConf(), SORT_INPUT_PATH);
+      
+      // Run sort
+      runSort(mr.createJobConf(), SORT_INPUT_PATH, SORT_OUTPUT_PATH);
+    } finally {
+      if (dfs != null) { dfs.shutdown(); }
+      if (mr != null) { mr.shutdown();
+      }
+    }
+  }
+
+}