mapreduce/src/test/mapred/org/apache/hadoop/mapred/TestLazyOutput.java

/**
 * 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 java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.Writer;
import java.util.Arrays;
import java.util.Iterator;
import java.util.List;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.FileUtil;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.hdfs.MiniDFSCluster;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.io.Writable;
import org.apache.hadoop.io.WritableComparable;
import org.apache.hadoop.mapred.lib.LazyOutputFormat;
import junit.framework.TestCase;

/**
 * A JUnit test to test the Map-Reduce framework's feature to create part
 * files only if there is an explicit output.collect. This helps in preventing
 * 0 byte files
 */
public class TestLazyOutput extends TestCase {
  private static final int NUM_HADOOP_SLAVES = 3;
  private static final int NUM_MAPS_PER_NODE = 2;
  private static final Path INPUT = new Path("/testlazy/input");

  private static final List<String> input = 
    Arrays.asList("All","Roads","Lead","To","Hadoop");


  static class TestMapper extends MapReduceBase
  implements Mapper<LongWritable, Text, LongWritable, Text> {
    private String id;

    public void configure(JobConf job) {
      id = job.get(JobContext.TASK_ATTEMPT_ID);
    }

    public void map(LongWritable key, Text val,
        OutputCollector<LongWritable, Text> output, Reporter reporter)
    throws IOException {
      // Everybody other than id 0 outputs
      if (!id.endsWith("0_0")) {
        output.collect(key, val);
      }
    }
  }

  static class TestReducer  extends MapReduceBase 
  implements Reducer<LongWritable, Text, LongWritable, Text> {
    private String id;

    public void configure(JobConf job) {
      id = job.get(JobContext.TASK_ATTEMPT_ID);
    }

    /** Writes all keys and values directly to output. */
    public void reduce(LongWritable key, Iterator<Text> values,
        OutputCollector<LongWritable, Text> output, Reporter reporter)
    throws IOException {
      while (values.hasNext()) {
        Text v = values.next();
        //Reducer 0 skips collect
        if (!id.endsWith("0_0")) {
          output.collect(key, v);
        }
      }
    }
  }

  private static void runTestLazyOutput(JobConf job, Path output,
      int numReducers, boolean createLazily) 
  throws Exception {

    job.setJobName("test-lazy-output");

    FileInputFormat.setInputPaths(job, INPUT);
    FileOutputFormat.setOutputPath(job, output);
    job.setInputFormat(TextInputFormat.class);
    job.setMapOutputKeyClass(LongWritable.class);
    job.setMapOutputValueClass(Text.class);
    job.setOutputKeyClass(LongWritable.class);
    job.setOutputValueClass(Text.class);

    job.setMapperClass(TestMapper.class);        
    job.setReducerClass(TestReducer.class);

    JobClient client = new JobClient(job);
    job.setNumReduceTasks(numReducers);
    if (createLazily) {
      LazyOutputFormat.setOutputFormatClass
        (job, TextOutputFormat.class);
    } else {
      job.setOutputFormat(TextOutputFormat.class);
    }

    JobClient.runJob(job);
  }

  public void createInput(FileSystem fs, int numMappers) throws Exception {
    for (int i =0; i < numMappers; i++) {
      OutputStream os = fs.create(new Path(INPUT, 
        "text" + i + ".txt"));
      Writer wr = new OutputStreamWriter(os);
      for(String inp : input) {
        wr.write(inp+"\n");
      }
      wr.close();
    }
  }


  public void testLazyOutput() 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);

      int numReducers = 2;
      int numMappers = NUM_HADOOP_SLAVES * NUM_MAPS_PER_NODE;

      createInput(fileSys, numMappers);
      Path output1 = new Path("/testlazy/output1");

      // Test 1. 
      runTestLazyOutput(mr.createJobConf(), output1, 
          numReducers, true);

      Path[] fileList = 
        FileUtil.stat2Paths(fileSys.listStatus(output1,
            new Utils.OutputFileUtils.OutputFilesFilter()));
      for(int i=0; i < fileList.length; ++i) {
        System.out.println("Test1 File list[" + i + "]" + ": "+ fileList[i]);
      }
      assertTrue(fileList.length == (numReducers - 1));

      // Test 2. 0 Reducers, maps directly write to the output files
      Path output2 = new Path("/testlazy/output2");
      runTestLazyOutput(mr.createJobConf(), output2, 0, true);

      fileList =
        FileUtil.stat2Paths(fileSys.listStatus(output2,
            new Utils.OutputFileUtils.OutputFilesFilter()));
      for(int i=0; i < fileList.length; ++i) {
        System.out.println("Test2 File list[" + i + "]" + ": "+ fileList[i]);
      }

      assertTrue(fileList.length == numMappers - 1);

      // Test 3. 0 Reducers, but flag is turned off
      Path output3 = new Path("/testlazy/output3");
      runTestLazyOutput(mr.createJobConf(), output3, 0, false);

      fileList =
        FileUtil.stat2Paths(fileSys.listStatus(output3,
            new Utils.OutputFileUtils.OutputFilesFilter()));
      for(int i=0; i < fileList.length; ++i) {
        System.out.println("Test3 File list[" + i + "]" + ": "+ fileList[i]);
      }

      assertTrue(fileList.length == numMappers);

    } finally {
      if (dfs != null) { dfs.shutdown(); }
      if (mr != null) { mr.shutdown();
      }
    }
  }
}