001/**
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *     http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018
019package org.apache.hadoop.mapred;
020
021import java.io.IOException;
022import java.text.NumberFormat;
023
024import org.apache.hadoop.classification.InterfaceAudience;
025import org.apache.hadoop.classification.InterfaceStability;
026import org.apache.hadoop.fs.FileSystem;
027import org.apache.hadoop.fs.Path;
028import org.apache.hadoop.io.compress.CompressionCodec;
029import org.apache.hadoop.mapred.FileAlreadyExistsException;
030import org.apache.hadoop.mapreduce.security.TokenCache;
031import org.apache.hadoop.util.Progressable;
032
033/** A base class for {@link OutputFormat}. */
034@InterfaceAudience.Public
035@InterfaceStability.Stable
036public abstract class FileOutputFormat<K, V> implements OutputFormat<K, V> {
037
038  /**
039   * Set whether the output of the job is compressed.
040   * @param conf the {@link JobConf} to modify
041   * @param compress should the output of the job be compressed?
042   */
043  public static void setCompressOutput(JobConf conf, boolean compress) {
044    conf.setBoolean(org.apache.hadoop.mapreduce.lib.output.
045      FileOutputFormat.COMPRESS, compress);
046  }
047  
048  /**
049   * Is the job output compressed?
050   * @param conf the {@link JobConf} to look in
051   * @return <code>true</code> if the job output should be compressed,
052   *         <code>false</code> otherwise
053   */
054  public static boolean getCompressOutput(JobConf conf) {
055    return conf.getBoolean(org.apache.hadoop.mapreduce.lib.output.
056      FileOutputFormat.COMPRESS, false);
057  }
058  
059  /**
060   * Set the {@link CompressionCodec} to be used to compress job outputs.
061   * @param conf the {@link JobConf} to modify
062   * @param codecClass the {@link CompressionCodec} to be used to
063   *                   compress the job outputs
064   */
065  public static void 
066  setOutputCompressorClass(JobConf conf, 
067                           Class<? extends CompressionCodec> codecClass) {
068    setCompressOutput(conf, true);
069    conf.setClass(org.apache.hadoop.mapreduce.lib.output.
070      FileOutputFormat.COMPRESS_CODEC, codecClass, 
071                  CompressionCodec.class);
072  }
073  
074  /**
075   * Get the {@link CompressionCodec} for compressing the job outputs.
076   * @param conf the {@link JobConf} to look in
077   * @param defaultValue the {@link CompressionCodec} to return if not set
078   * @return the {@link CompressionCodec} to be used to compress the 
079   *         job outputs
080   * @throws IllegalArgumentException if the class was specified, but not found
081   */
082  public static Class<? extends CompressionCodec> 
083  getOutputCompressorClass(JobConf conf, 
084                                       Class<? extends CompressionCodec> defaultValue) {
085    Class<? extends CompressionCodec> codecClass = defaultValue;
086    
087    String name = conf.get(org.apache.hadoop.mapreduce.lib.output.
088      FileOutputFormat.COMPRESS_CODEC);
089    if (name != null) {
090      try {
091        codecClass = 
092                conf.getClassByName(name).asSubclass(CompressionCodec.class);
093      } catch (ClassNotFoundException e) {
094        throw new IllegalArgumentException("Compression codec " + name + 
095                                           " was not found.", e);
096      }
097    }
098    return codecClass;
099  }
100  
101  public abstract RecordWriter<K, V> getRecordWriter(FileSystem ignored,
102                                               JobConf job, String name,
103                                               Progressable progress)
104    throws IOException;
105
106  public void checkOutputSpecs(FileSystem ignored, JobConf job) 
107    throws FileAlreadyExistsException, 
108           InvalidJobConfException, IOException {
109    // Ensure that the output directory is set and not already there
110    Path outDir = getOutputPath(job);
111    if (outDir == null && job.getNumReduceTasks() != 0) {
112      throw new InvalidJobConfException("Output directory not set in JobConf.");
113    }
114    if (outDir != null) {
115      FileSystem fs = outDir.getFileSystem(job);
116      // normalize the output directory
117      outDir = fs.makeQualified(outDir);
118      setOutputPath(job, outDir);
119      
120      // get delegation token for the outDir's file system
121      TokenCache.obtainTokensForNamenodes(job.getCredentials(), 
122                                          new Path[] {outDir}, job);
123      
124      // check its existence
125      if (fs.exists(outDir)) {
126        throw new FileAlreadyExistsException("Output directory " + outDir + 
127                                             " already exists");
128      }
129    }
130  }
131
132  /**
133   * Set the {@link Path} of the output directory for the map-reduce job.
134   *
135   * @param conf The configuration of the job.
136   * @param outputDir the {@link Path} of the output directory for 
137   * the map-reduce job.
138   */
139  public static void setOutputPath(JobConf conf, Path outputDir) {
140    outputDir = new Path(conf.getWorkingDirectory(), outputDir);
141    conf.set(org.apache.hadoop.mapreduce.lib.output.
142      FileOutputFormat.OUTDIR, outputDir.toString());
143  }
144
145  /**
146   * Set the {@link Path} of the task's temporary output directory 
147   * for the map-reduce job.
148   * 
149   * <p><i>Note</i>: Task output path is set by the framework.
150   * </p>
151   * @param conf The configuration of the job.
152   * @param outputDir the {@link Path} of the output directory 
153   * for the map-reduce job.
154   */
155  
156  static void setWorkOutputPath(JobConf conf, Path outputDir) {
157    outputDir = new Path(conf.getWorkingDirectory(), outputDir);
158    conf.set(JobContext.TASK_OUTPUT_DIR, outputDir.toString());
159  }
160  
161  /**
162   * Get the {@link Path} to the output directory for the map-reduce job.
163   * 
164   * @return the {@link Path} to the output directory for the map-reduce job.
165   * @see FileOutputFormat#getWorkOutputPath(JobConf)
166   */
167  public static Path getOutputPath(JobConf conf) {
168    String name = conf.get(org.apache.hadoop.mapreduce.lib.output.
169      FileOutputFormat.OUTDIR);
170    return name == null ? null: new Path(name);
171  }
172  
173  /**
174   *  Get the {@link Path} to the task's temporary output directory 
175   *  for the map-reduce job
176   *  
177   * <h4 id="SideEffectFiles">Tasks' Side-Effect Files</h4>
178   * 
179   * <p><i>Note:</i> The following is valid only if the {@link OutputCommitter}
180   *  is {@link FileOutputCommitter}. If <code>OutputCommitter</code> is not 
181   *  a <code>FileOutputCommitter</code>, the task's temporary output
182   *  directory is same as {@link #getOutputPath(JobConf)} i.e.
183   *  <tt>${mapreduce.output.fileoutputformat.outputdir}$</tt></p>
184   *  
185   * <p>Some applications need to create/write-to side-files, which differ from
186   * the actual job-outputs.
187   * 
188   * <p>In such cases there could be issues with 2 instances of the same TIP 
189   * (running simultaneously e.g. speculative tasks) trying to open/write-to the
190   * same file (path) on HDFS. Hence the application-writer will have to pick 
191   * unique names per task-attempt (e.g. using the attemptid, say 
192   * <tt>attempt_200709221812_0001_m_000000_0</tt>), not just per TIP.</p> 
193   * 
194   * <p>To get around this the Map-Reduce framework helps the application-writer 
195   * out by maintaining a special 
196   * <tt>${mapreduce.output.fileoutputformat.outputdir}/_temporary/_${taskid}</tt> 
197   * sub-directory for each task-attempt on HDFS where the output of the 
198   * task-attempt goes. On successful completion of the task-attempt the files 
199   * in the <tt>${mapreduce.output.fileoutputformat.outputdir}/_temporary/_${taskid}</tt> (only) 
200   * are <i>promoted</i> to <tt>${mapreduce.output.fileoutputformat.outputdir}</tt>. Of course, the 
201   * framework discards the sub-directory of unsuccessful task-attempts. This 
202   * is completely transparent to the application.</p>
203   * 
204   * <p>The application-writer can take advantage of this by creating any 
205   * side-files required in <tt>${mapreduce.task.output.dir}</tt> during execution 
206   * of his reduce-task i.e. via {@link #getWorkOutputPath(JobConf)}, and the 
207   * framework will move them out similarly - thus she doesn't have to pick 
208   * unique paths per task-attempt.</p>
209   * 
210   * <p><i>Note</i>: the value of <tt>${mapreduce.task.output.dir}</tt> during 
211   * execution of a particular task-attempt is actually 
212   * <tt>${mapreduce.output.fileoutputformat.outputdir}/_temporary/_{$taskid}</tt>, and this value is 
213   * set by the map-reduce framework. So, just create any side-files in the 
214   * path  returned by {@link #getWorkOutputPath(JobConf)} from map/reduce 
215   * task to take advantage of this feature.</p>
216   * 
217   * <p>The entire discussion holds true for maps of jobs with 
218   * reducer=NONE (i.e. 0 reduces) since output of the map, in that case, 
219   * goes directly to HDFS.</p> 
220   * 
221   * @return the {@link Path} to the task's temporary output directory 
222   * for the map-reduce job.
223   */
224  public static Path getWorkOutputPath(JobConf conf) {
225    String name = conf.get(JobContext.TASK_OUTPUT_DIR);
226    return name == null ? null: new Path(name);
227  }
228
229  /**
230   * Helper function to create the task's temporary output directory and 
231   * return the path to the task's output file.
232   * 
233   * @param conf job-configuration
234   * @param name temporary task-output filename
235   * @return path to the task's temporary output file
236   * @throws IOException
237   */
238  public static Path getTaskOutputPath(JobConf conf, String name) 
239  throws IOException {
240    // ${mapred.out.dir}
241    Path outputPath = getOutputPath(conf);
242    if (outputPath == null) {
243      throw new IOException("Undefined job output-path");
244    }
245
246    OutputCommitter committer = conf.getOutputCommitter();
247    Path workPath = outputPath;
248    TaskAttemptContext context = 
249      new TaskAttemptContextImpl(conf,
250                                 TaskAttemptID.forName(conf.get(
251                                     JobContext.TASK_ATTEMPT_ID)));
252    if (committer instanceof FileOutputCommitter) {
253      workPath = ((FileOutputCommitter)committer).getWorkPath(context,
254                                                              outputPath);
255    }
256    
257    // ${mapred.out.dir}/_temporary/_${taskid}/${name}
258    return new Path(workPath, name);
259  } 
260
261  /**
262   * Helper function to generate a name that is unique for the task.
263   *
264   * <p>The generated name can be used to create custom files from within the
265   * different tasks for the job, the names for different tasks will not collide
266   * with each other.</p>
267   *
268   * <p>The given name is postfixed with the task type, 'm' for maps, 'r' for
269   * reduces and the task partition number. For example, give a name 'test'
270   * running on the first map o the job the generated name will be
271   * 'test-m-00000'.</p>
272   *
273   * @param conf the configuration for the job.
274   * @param name the name to make unique.
275   * @return a unique name accross all tasks of the job.
276   */
277  public static String getUniqueName(JobConf conf, String name) {
278    int partition = conf.getInt(JobContext.TASK_PARTITION, -1);
279    if (partition == -1) {
280      throw new IllegalArgumentException(
281        "This method can only be called from within a Job");
282    }
283
284    String taskType = (conf.getBoolean(JobContext.TASK_ISMAP, true)) ? "m" : "r";
285
286    NumberFormat numberFormat = NumberFormat.getInstance();
287    numberFormat.setMinimumIntegerDigits(5);
288    numberFormat.setGroupingUsed(false);
289
290    return name + "-" + taskType + "-" + numberFormat.format(partition);
291  }
292
293  /**
294   * Helper function to generate a {@link Path} for a file that is unique for
295   * the task within the job output directory.
296   *
297   * <p>The path can be used to create custom files from within the map and
298   * reduce tasks. The path name will be unique for each task. The path parent
299   * will be the job output directory.</p>ls
300   *
301   * <p>This method uses the {@link #getUniqueName} method to make the file name
302   * unique for the task.</p>
303   *
304   * @param conf the configuration for the job.
305   * @param name the name for the file.
306   * @return a unique path accross all tasks of the job.
307   */
308  public static Path getPathForCustomFile(JobConf conf, String name) {
309    return new Path(getWorkOutputPath(conf), getUniqueName(conf, name));
310  }
311}
312