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@@ -252,11 +252,20 @@ document.write("Last Published: " + document.lastModified);
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<a href="#Task+Execution+%26+Environment">Task Execution & Environment</a>
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<ul class="minitoc">
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<li>
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+<a href="#Memory+management"> Memory management</a>
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+</li>
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+<li>
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<a href="#Map+Parameters">Map Parameters</a>
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</li>
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<li>
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<a href="#Shuffle%2FReduce+Parameters">Shuffle/Reduce Parameters</a>
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</li>
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+<li>
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+<a href="#Directory+Structure"> Directory Structure </a>
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+</li>
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+<li>
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+<a href="#Task+JVM+Reuse">Task JVM Reuse</a>
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+</li>
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</ul>
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</li>
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<li>
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@@ -330,7 +339,7 @@ document.write("Last Published: " + document.lastModified);
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<a href="#Example%3A+WordCount+v2.0">Example: WordCount v2.0</a>
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<ul class="minitoc">
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<li>
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-<a href="#Source+Code-N10F78">Source Code</a>
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+<a href="#Source+Code-N10F9A">Source Code</a>
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</li>
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<li>
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<a href="#Sample+Runs">Sample Runs</a>
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@@ -1588,6 +1597,8 @@ document.write("Last Published: " + document.lastModified);
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<span class="codefrag"></property></span>
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</p>
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+<a name="N108BF"></a><a name="Memory+management"></a>
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+<h4> Memory management</h4>
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<p>Users/admins can also specify the maximum virtual memory
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of the launched child-task, and any sub-process it launches
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recursively, using <span class="codefrag">mapred.child.ulimit</span>. Note that
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@@ -1629,7 +1640,7 @@ document.write("Last Published: " + document.lastModified);
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counters for a job- particularly relative to byte counts from the map
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and into the reduce- is invaluable to the tuning of these
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parameters.</p>
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-<a name="N108E9"></a><a name="Map+Parameters"></a>
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+<a name="N108F0"></a><a name="Map+Parameters"></a>
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<h4>Map Parameters</h4>
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<p>A record emitted from a map will be serialized into a buffer and
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metadata will be stored into accounting buffers. As described in the
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@@ -1703,7 +1714,7 @@ document.write("Last Published: " + document.lastModified);
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combiner.</li>
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</ul>
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-<a name="N10955"></a><a name="Shuffle%2FReduce+Parameters"></a>
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+<a name="N1095C"></a><a name="Shuffle%2FReduce+Parameters"></a>
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<h4>Shuffle/Reduce Parameters</h4>
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<p>As described previously, each reduce fetches the output assigned
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to it by the Partitioner via HTTP into memory and periodically
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@@ -1799,6 +1810,8 @@ document.write("Last Published: " + document.lastModified);
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of the intermediate merge.</li>
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</ul>
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+<a name="N109D7"></a><a name="Directory+Structure"></a>
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+<h4> Directory Structure </h4>
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<p>The task tracker has local directory,
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<span class="codefrag"> ${mapred.local.dir}/taskTracker/</span> to create localized
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cache and localized job. It can define multiple local directories
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@@ -1869,7 +1882,9 @@ document.write("Last Published: " + document.lastModified);
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<li>
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<span class="codefrag">${mapred.local.dir}/taskTracker/jobcache/$jobid/$taskid/work</span>
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- : The curernt working directory of the task. </li>
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+ : The curernt working directory of the task.
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+ With <a href="#Task+JVM+Reuse">jvm reuse</a> enabled for tasks, this
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+ directory will be the directory on which the jvm has started</li>
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<li>
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<span class="codefrag">${mapred.local.dir}/taskTracker/jobcache/$jobid/$taskid/work/tmp</span>
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@@ -1896,6 +1911,17 @@ document.write("Last Published: " + document.lastModified);
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</li>
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</ul>
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+<a name="N10A46"></a><a name="Task+JVM+Reuse"></a>
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+<h4>Task JVM Reuse</h4>
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+<p>Jobs can enable task JVMs to be reused by specifying the job
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+ configuration <span class="codefrag">mapred.job.reuse.jvm.num.tasks</span>. If the
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+ value is 1 (the default), then JVMs are not reused
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+ (i.e. 1 task per JVM). If it is -1, there is no limit to the number
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+ of tasks a JVM can run (of the same job). One can also specify some
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+ value greater than 1 using the api
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+ <a href="api/org/apache/hadoop/mapred/JobConf.html#setNumTasksToExecutePerJvm(int)">
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+ JobConf.setNumTasksToExecutePerJvm(int)</a>
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+</p>
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<p>The following properties are localized in the job configuration
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for each task's execution: </p>
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<table class="ForrestTable" cellspacing="1" cellpadding="4">
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@@ -1977,7 +2003,7 @@ document.write("Last Published: " + document.lastModified);
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<a href="native_libraries.html#Loading+native+libraries+through+DistributedCache">
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native_libraries.html</a>
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</p>
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-<a name="N10B0D"></a><a name="Job+Submission+and+Monitoring"></a>
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+<a name="N10B2F"></a><a name="Job+Submission+and+Monitoring"></a>
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<h3 class="h4">Job Submission and Monitoring</h3>
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<p>
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<a href="api/org/apache/hadoop/mapred/JobClient.html">
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@@ -2038,7 +2064,7 @@ document.write("Last Published: " + document.lastModified);
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<p>Normally the user creates the application, describes various facets
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of the job via <span class="codefrag">JobConf</span>, and then uses the
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<span class="codefrag">JobClient</span> to submit the job and monitor its progress.</p>
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-<a name="N10B6D"></a><a name="Job+Control"></a>
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+<a name="N10B8F"></a><a name="Job+Control"></a>
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<h4>Job Control</h4>
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<p>Users may need to chain Map/Reduce jobs to accomplish complex
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tasks which cannot be done via a single Map/Reduce job. This is fairly
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@@ -2074,7 +2100,7 @@ document.write("Last Published: " + document.lastModified);
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</li>
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</ul>
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-<a name="N10B97"></a><a name="Job+Input"></a>
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+<a name="N10BB9"></a><a name="Job+Input"></a>
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<h3 class="h4">Job Input</h3>
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<p>
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<a href="api/org/apache/hadoop/mapred/InputFormat.html">
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@@ -2122,7 +2148,7 @@ document.write("Last Published: " + document.lastModified);
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appropriate <span class="codefrag">CompressionCodec</span>. However, it must be noted that
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compressed files with the above extensions cannot be <em>split</em> and
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each compressed file is processed in its entirety by a single mapper.</p>
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-<a name="N10C01"></a><a name="InputSplit"></a>
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+<a name="N10C23"></a><a name="InputSplit"></a>
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<h4>InputSplit</h4>
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<p>
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<a href="api/org/apache/hadoop/mapred/InputSplit.html">
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@@ -2136,7 +2162,7 @@ document.write("Last Published: " + document.lastModified);
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FileSplit</a> is the default <span class="codefrag">InputSplit</span>. It sets
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|
<span class="codefrag">map.input.file</span> to the path of the input file for the
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|
logical split.</p>
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-<a name="N10C26"></a><a name="RecordReader"></a>
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+<a name="N10C48"></a><a name="RecordReader"></a>
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<h4>RecordReader</h4>
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<p>
|
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<a href="api/org/apache/hadoop/mapred/RecordReader.html">
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@@ -2148,7 +2174,7 @@ document.write("Last Published: " + document.lastModified);
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for processing. <span class="codefrag">RecordReader</span> thus assumes the
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responsibility of processing record boundaries and presents the tasks
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with keys and values.</p>
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-<a name="N10C49"></a><a name="Job+Output"></a>
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+<a name="N10C6B"></a><a name="Job+Output"></a>
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<h3 class="h4">Job Output</h3>
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<p>
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<a href="api/org/apache/hadoop/mapred/OutputFormat.html">
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@@ -2173,7 +2199,7 @@ document.write("Last Published: " + document.lastModified);
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<p>
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<span class="codefrag">TextOutputFormat</span> is the default
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|
<span class="codefrag">OutputFormat</span>.</p>
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-<a name="N10C72"></a><a name="OutputCommitter"></a>
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+<a name="N10C94"></a><a name="OutputCommitter"></a>
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<h4>OutputCommitter</h4>
|
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<p>
|
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<a href="api/org/apache/hadoop/mapred/OutputCommitter.html">
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@@ -2215,7 +2241,7 @@ document.write("Last Published: " + document.lastModified);
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<p>
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<span class="codefrag">FileOutputCommitter</span> is the default
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<span class="codefrag">OutputCommitter</span>.</p>
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-<a name="N10CA2"></a><a name="Task+Side-Effect+Files"></a>
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+<a name="N10CC4"></a><a name="Task+Side-Effect+Files"></a>
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<h4>Task Side-Effect Files</h4>
|
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<p>In some applications, component tasks need to create and/or write to
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side-files, which differ from the actual job-output files.</p>
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@@ -2256,7 +2282,7 @@ document.write("Last Published: " + document.lastModified);
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<p>The entire discussion holds true for maps of jobs with
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reducer=NONE (i.e. 0 reduces) since output of the map, in that case,
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goes directly to HDFS.</p>
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-<a name="N10CF0"></a><a name="RecordWriter"></a>
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+<a name="N10D12"></a><a name="RecordWriter"></a>
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<h4>RecordWriter</h4>
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<p>
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<a href="api/org/apache/hadoop/mapred/RecordWriter.html">
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@@ -2264,9 +2290,9 @@ document.write("Last Published: " + document.lastModified);
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pairs to an output file.</p>
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<p>RecordWriter implementations write the job outputs to the
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<span class="codefrag">FileSystem</span>.</p>
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-<a name="N10D07"></a><a name="Other+Useful+Features"></a>
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+<a name="N10D29"></a><a name="Other+Useful+Features"></a>
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<h3 class="h4">Other Useful Features</h3>
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-<a name="N10D0D"></a><a name="Counters"></a>
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+<a name="N10D2F"></a><a name="Counters"></a>
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<h4>Counters</h4>
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<p>
|
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|
<span class="codefrag">Counters</span> represent global counters, defined either by
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@@ -2283,7 +2309,7 @@ document.write("Last Published: " + document.lastModified);
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in the <span class="codefrag">map</span> and/or
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|
<span class="codefrag">reduce</span> methods. These counters are then globally
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|
aggregated by the framework.</p>
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-<a name="N10D3C"></a><a name="DistributedCache"></a>
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+<a name="N10D5E"></a><a name="DistributedCache"></a>
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|
<h4>DistributedCache</h4>
|
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<p>
|
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<a href="api/org/apache/hadoop/filecache/DistributedCache.html">
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@@ -2354,7 +2380,7 @@ document.write("Last Published: " + document.lastModified);
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<span class="codefrag">mapred.job.classpath.{files|archives}</span>. Similarly the
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cached files that are symlinked into the working directory of the
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task can be used to distribute native libraries and load them.</p>
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-<a name="N10DBF"></a><a name="Tool"></a>
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+<a name="N10DE1"></a><a name="Tool"></a>
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<h4>Tool</h4>
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|
<p>The <a href="api/org/apache/hadoop/util/Tool.html">Tool</a>
|
|
|
interface supports the handling of generic Hadoop command-line options.
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@@ -2394,7 +2420,7 @@ document.write("Last Published: " + document.lastModified);
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</span>
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</p>
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-<a name="N10DF1"></a><a name="IsolationRunner"></a>
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+<a name="N10E13"></a><a name="IsolationRunner"></a>
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<h4>IsolationRunner</h4>
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<p>
|
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<a href="api/org/apache/hadoop/mapred/IsolationRunner.html">
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@@ -2418,7 +2444,7 @@ document.write("Last Published: " + document.lastModified);
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<p>
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<span class="codefrag">IsolationRunner</span> will run the failed task in a single
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jvm, which can be in the debugger, over precisely the same input.</p>
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-<a name="N10E24"></a><a name="Profiling"></a>
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+<a name="N10E46"></a><a name="Profiling"></a>
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<h4>Profiling</h4>
|
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<p>Profiling is a utility to get a representative (2 or 3) sample
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|
|
of built-in java profiler for a sample of maps and reduces. </p>
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@@ -2451,7 +2477,7 @@ document.write("Last Published: " + document.lastModified);
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<span class="codefrag">-agentlib:hprof=cpu=samples,heap=sites,force=n,thread=y,verbose=n,file=%s</span>
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</p>
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-<a name="N10E58"></a><a name="Debugging"></a>
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+<a name="N10E7A"></a><a name="Debugging"></a>
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<h4>Debugging</h4>
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<p>Map/Reduce framework provides a facility to run user-provided
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scripts for debugging. When map/reduce task fails, user can run
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@@ -2462,14 +2488,14 @@ document.write("Last Published: " + document.lastModified);
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<p> In the following sections we discuss how to submit debug script
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along with the job. For submitting debug script, first it has to
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distributed. Then the script has to supplied in Configuration. </p>
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-<a name="N10E64"></a><a name="How+to+distribute+script+file%3A"></a>
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+<a name="N10E86"></a><a name="How+to+distribute+script+file%3A"></a>
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<h5> How to distribute script file: </h5>
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<p>
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The user has to use
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<a href="mapred_tutorial.html#DistributedCache">DistributedCache</a>
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mechanism to <em>distribute</em> and <em>symlink</em> the
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debug script file.</p>
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-<a name="N10E78"></a><a name="How+to+submit+script%3A"></a>
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+<a name="N10E9A"></a><a name="How+to+submit+script%3A"></a>
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<h5> How to submit script: </h5>
|
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<p> A quick way to submit debug script is to set values for the
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properties "mapred.map.task.debug.script" and
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@@ -2493,17 +2519,17 @@ document.write("Last Published: " + document.lastModified);
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<span class="codefrag">$script $stdout $stderr $syslog $jobconf $program </span>
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</p>
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-<a name="N10E9A"></a><a name="Default+Behavior%3A"></a>
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+<a name="N10EBC"></a><a name="Default+Behavior%3A"></a>
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<h5> Default Behavior: </h5>
|
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<p> For pipes, a default script is run to process core dumps under
|
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|
gdb, prints stack trace and gives info about running threads. </p>
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-<a name="N10EA5"></a><a name="JobControl"></a>
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+<a name="N10EC7"></a><a name="JobControl"></a>
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<h4>JobControl</h4>
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<p>
|
|
|
<a href="api/org/apache/hadoop/mapred/jobcontrol/package-summary.html">
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|
JobControl</a> is a utility which encapsulates a set of Map/Reduce jobs
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|
and their dependencies.</p>
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-<a name="N10EB2"></a><a name="Data+Compression"></a>
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+<a name="N10ED4"></a><a name="Data+Compression"></a>
|
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<h4>Data Compression</h4>
|
|
|
<p>Hadoop Map/Reduce provides facilities for the application-writer to
|
|
|
specify compression for both intermediate map-outputs and the
|
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@@ -2517,7 +2543,7 @@ document.write("Last Published: " + document.lastModified);
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codecs for reasons of both performance (zlib) and non-availability of
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Java libraries (lzo). More details on their usage and availability are
|
|
|
available <a href="native_libraries.html">here</a>.</p>
|
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|
-<a name="N10ED2"></a><a name="Intermediate+Outputs"></a>
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|
|
+<a name="N10EF4"></a><a name="Intermediate+Outputs"></a>
|
|
|
<h5>Intermediate Outputs</h5>
|
|
|
<p>Applications can control compression of intermediate map-outputs
|
|
|
via the
|
|
|
@@ -2526,7 +2552,7 @@ document.write("Last Published: " + document.lastModified);
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|
|
<span class="codefrag">CompressionCodec</span> to be used via the
|
|
|
<a href="api/org/apache/hadoop/mapred/JobConf.html#setMapOutputCompressorClass(java.lang.Class)">
|
|
|
JobConf.setMapOutputCompressorClass(Class)</a> api.</p>
|
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-<a name="N10EE7"></a><a name="Job+Outputs"></a>
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|
|
+<a name="N10F09"></a><a name="Job+Outputs"></a>
|
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|
<h5>Job Outputs</h5>
|
|
|
<p>Applications can control compression of job-outputs via the
|
|
|
<a href="api/org/apache/hadoop/mapred/FileOutputFormat.html#setCompressOutput(org.apache.hadoop.mapred.JobConf,%20boolean)">
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@@ -2543,7 +2569,7 @@ document.write("Last Published: " + document.lastModified);
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<a href="api/org/apache/hadoop/mapred/SequenceFileOutputFormat.html#setOutputCompressionType(org.apache.hadoop.mapred.JobConf,%20org.apache.hadoop.io.SequenceFile.CompressionType)">
|
|
|
SequenceFileOutputFormat.setOutputCompressionType(JobConf,
|
|
|
SequenceFile.CompressionType)</a> api.</p>
|
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-<a name="N10F14"></a><a name="Skipping+Bad+Records"></a>
|
|
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+<a name="N10F36"></a><a name="Skipping+Bad+Records"></a>
|
|
|
<h4>Skipping Bad Records</h4>
|
|
|
<p>Hadoop provides an optional mode of execution in which the bad
|
|
|
records are detected and skipped in further attempts.
|
|
|
@@ -2617,7 +2643,7 @@ document.write("Last Published: " + document.lastModified);
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</div>
|
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|
|
-<a name="N10F5E"></a><a name="Example%3A+WordCount+v2.0"></a>
|
|
|
+<a name="N10F80"></a><a name="Example%3A+WordCount+v2.0"></a>
|
|
|
<h2 class="h3">Example: WordCount v2.0</h2>
|
|
|
<div class="section">
|
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<p>Here is a more complete <span class="codefrag">WordCount</span> which uses many of the
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@@ -2627,7 +2653,7 @@ document.write("Last Published: " + document.lastModified);
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<a href="quickstart.html#SingleNodeSetup">pseudo-distributed</a> or
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<a href="quickstart.html#Fully-Distributed+Operation">fully-distributed</a>
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Hadoop installation.</p>
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-<a name="N10F78"></a><a name="Source+Code-N10F78"></a>
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+<a name="N10F9A"></a><a name="Source+Code-N10F9A"></a>
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<h3 class="h4">Source Code</h3>
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<table class="ForrestTable" cellspacing="1" cellpadding="4">
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</tr>
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</table>
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-<a name="N116DA"></a><a name="Sample+Runs"></a>
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+<a name="N116FC"></a><a name="Sample+Runs"></a>
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<h3 class="h4">Sample Runs</h3>
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<p>Sample text-files as input:</p>
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<p>
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<br>
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</p>
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-<a name="N117AE"></a><a name="Highlights"></a>
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+<a name="N117D0"></a><a name="Highlights"></a>
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<h3 class="h4">Highlights</h3>
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<p>The second version of <span class="codefrag">WordCount</span> improves upon the
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previous one by using some features offered by the Map/Reduce framework:
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Devaraj Das