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@@ -216,6 +216,9 @@ document.write("Last Published: " + document.lastModified);
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<a href="#Job+Configuration">Job Configuration</a>
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<a href="#Job+Configuration">Job Configuration</a>
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</li>
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</li>
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<li>
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<li>
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+<a href="#Task+Execution+%26+Environment">Task Execution & Environment</a>
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+</li>
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+<li>
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<a href="#Job+Submission+and+Monitoring">Job Submission and Monitoring</a>
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<a href="#Job+Submission+and+Monitoring">Job Submission and Monitoring</a>
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<ul class="minitoc">
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<ul class="minitoc">
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<li>
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<li>
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@@ -274,7 +277,7 @@ 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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<a href="#Example%3A+WordCount+v2.0">Example: WordCount v2.0</a>
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<ul class="minitoc">
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<ul class="minitoc">
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<li>
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<li>
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-<a href="#Source+Code-N10B1F">Source Code</a>
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+<a href="#Source+Code-N10B98">Source Code</a>
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</li>
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</li>
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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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<a href="#Sample+Runs">Sample Runs</a>
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@@ -1460,7 +1463,67 @@ document.write("Last Published: " + document.lastModified);
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<a href="api/org/apache/hadoop/conf/Configuration.html#set(java.lang.String, java.lang.String)">set(String, String)</a>/<a href="api/org/apache/hadoop/conf/Configuration.html#get(java.lang.String, java.lang.String)">get(String, String)</a>
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<a href="api/org/apache/hadoop/conf/Configuration.html#set(java.lang.String, java.lang.String)">set(String, String)</a>/<a href="api/org/apache/hadoop/conf/Configuration.html#get(java.lang.String, java.lang.String)">get(String, String)</a>
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to set/get arbitrary parameters needed by applications. However, use the
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to set/get arbitrary parameters needed by applications. However, use the
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<span class="codefrag">DistributedCache</span> for large amounts of (read-only) data.</p>
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<span class="codefrag">DistributedCache</span> for large amounts of (read-only) data.</p>
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-<a name="N1082C"></a><a name="Job+Submission+and+Monitoring"></a>
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+<a name="N1082C"></a><a name="Task+Execution+%26+Environment"></a>
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+<h3 class="h4">Task Execution & Environment</h3>
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+<p>The <span class="codefrag">TaskTracker</span> executes the <span class="codefrag">Mapper</span>/
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+ <span class="codefrag">Reducer</span> <em>task</em> as a child process in a separate jvm.
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+ </p>
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+<p>The child-task inherits the environment of the parent
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+ <span class="codefrag">TaskTracker</span>. The user can specify additional options to the
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+ child-jvm via the <span class="codefrag">mapred.child.java.opts</span> configuration
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+ parameter in the <span class="codefrag">JobConf</span> such as non-standard paths for the
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+ run-time linker to search shared libraries via
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+ <span class="codefrag">-Djava.library.path=<></span> etc. If the
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+ <span class="codefrag">mapred.child.java.opts</span> contains the symbol <em>@taskid@</em>
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+ it is interpolated with value of <span class="codefrag">taskid</span> of the map/reduce
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+ task.</p>
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+<p>Here is an example with multiple arguments and substitutions,
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+ showing jvm GC logging, and start of a passwordless JVM JMX agent so that
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+ it can connect with jconsole and the likes to watch child memory,
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+ threads and get thread dumps. It also sets the maximum heap-size of the
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+ child jvm to 512MB and adds an additional path to the
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+ <span class="codefrag">java.library.path</span> of the child-jvm.</p>
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+<p>
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+
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+<span class="codefrag"><property></span>
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+<br>
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+ <span class="codefrag"><name>mapred.child.java.opts</name></span>
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+<br>
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+ <span class="codefrag"><value></span>
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+<br>
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+ <span class="codefrag">
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+ -Xmx512M -Djava.library.path=/home/mycompany/lib
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+ -verbose:gc -Xloggc:/tmp/@taskid@.gc</span>
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+<br>
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+ <span class="codefrag">
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+ -Dcom.sun.management.jmxremote.authenticate=false
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+ -Dcom.sun.management.jmxremote.ssl=false</span>
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+<br>
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+ <span class="codefrag"></value></span>
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+<br>
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+
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+<span class="codefrag"></property></span>
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+
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+</p>
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+<p>The <a href="#DistributedCache">DistributedCache</a> can also be used
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+ as a rudimentary software distribution mechanism for use in the map
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+ and/or reduce tasks. It can be used to distribute both jars and
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+ native libraries. The
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+ <a href="api/org/apache/hadoop/filecache/DistributedCache.html#addArchiveToClassPath(org.apache.hadoop.fs.Path,%20org.apache.hadoop.conf.Configuration)">
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+ DistributedCache.addArchiveToClassPath(Path, Configuration)</a> or
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+ <a href="api/org/apache/hadoop/filecache/DistributedCache.html#addFileToClassPath(org.apache.hadoop.fs.Path,%20org.apache.hadoop.conf.Configuration)">
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+ DistributedCache.addFileToClassPath(Path, Configuration)</a> api can
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+ be used to cache files/jars and also add them to the <em>classpath</em>
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+ of child-jvm. Similarly the facility provided by the
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+ <span class="codefrag">DistributedCache</span> where-in it symlinks the cached files into
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+ the working directory of the task can be used to distribute native
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+ libraries and load them. The underlying detail is that child-jvm always
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+ has its <em>current working directory</em> added to the
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+ <span class="codefrag">java.library.path</span> and hence the cached libraries can be
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+ loaded via <a href="http://java.sun.com/j2se/1.5.0/docs/api/java/lang/System.html#loadLibrary(java.lang.String)">
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+ System.loadLibrary</a> or <a href="http://java.sun.com/j2se/1.5.0/docs/api/java/lang/System.html#load(java.lang.String)">
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+ System.load</a>.</p>
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+<a name="N108A1"></a><a name="Job+Submission+and+Monitoring"></a>
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<h3 class="h4">Job Submission and Monitoring</h3>
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<h3 class="h4">Job Submission and Monitoring</h3>
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<p>
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<p>
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<a href="api/org/apache/hadoop/mapred/JobClient.html">
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<a href="api/org/apache/hadoop/mapred/JobClient.html">
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@@ -1496,7 +1559,7 @@ document.write("Last Published: " + document.lastModified);
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<p>Normally the user creates the application, describes various facets
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<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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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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<span class="codefrag">JobClient</span> to submit the job and monitor its progress.</p>
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-<a name="N1086A"></a><a name="Job+Control"></a>
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+<a name="N108DF"></a><a name="Job+Control"></a>
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<h4>Job Control</h4>
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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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<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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tasks which cannot be done via a single map-reduce job. This is fairly
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@@ -1532,7 +1595,7 @@ document.write("Last Published: " + document.lastModified);
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</li>
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</li>
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</ul>
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</ul>
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-<a name="N10894"></a><a name="Job+Input"></a>
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+<a name="N10909"></a><a name="Job+Input"></a>
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<h3 class="h4">Job Input</h3>
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<h3 class="h4">Job Input</h3>
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<p>
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<p>
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<a href="api/org/apache/hadoop/mapred/InputFormat.html">
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<a href="api/org/apache/hadoop/mapred/InputFormat.html">
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@@ -1580,7 +1643,7 @@ 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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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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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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each compressed file is processed in its entirety by a single mapper.</p>
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-<a name="N108FE"></a><a name="InputSplit"></a>
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+<a name="N10973"></a><a name="InputSplit"></a>
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<h4>InputSplit</h4>
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<h4>InputSplit</h4>
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<p>
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<p>
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<a href="api/org/apache/hadoop/mapred/InputSplit.html">
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<a href="api/org/apache/hadoop/mapred/InputSplit.html">
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@@ -1594,7 +1657,7 @@ 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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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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<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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logical split.</p>
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-<a name="N10923"></a><a name="RecordReader"></a>
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+<a name="N10998"></a><a name="RecordReader"></a>
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<h4>RecordReader</h4>
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<h4>RecordReader</h4>
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<p>
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<p>
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<a href="api/org/apache/hadoop/mapred/RecordReader.html">
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<a href="api/org/apache/hadoop/mapred/RecordReader.html">
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@@ -1606,7 +1669,7 @@ document.write("Last Published: " + document.lastModified);
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for processing. <span class="codefrag">RecordReader</span> thus assumes the
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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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responsibility of processing record boundaries and presents the tasks
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with keys and values.</p>
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with keys and values.</p>
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-<a name="N10946"></a><a name="Job+Output"></a>
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+<a name="N109BB"></a><a name="Job+Output"></a>
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<h3 class="h4">Job Output</h3>
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<h3 class="h4">Job Output</h3>
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<p>
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<p>
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<a href="api/org/apache/hadoop/mapred/OutputFormat.html">
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<a href="api/org/apache/hadoop/mapred/OutputFormat.html">
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@@ -1631,7 +1694,7 @@ document.write("Last Published: " + document.lastModified);
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<p>
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<p>
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<span class="codefrag">TextOutputFormat</span> is the default
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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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<span class="codefrag">OutputFormat</span>.</p>
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-<a name="N1096F"></a><a name="Task+Side-Effect+Files"></a>
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+<a name="N109E4"></a><a name="Task+Side-Effect+Files"></a>
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<h4>Task Side-Effect Files</h4>
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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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<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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side-files, which differ from the actual job-output files.</p>
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@@ -1657,7 +1720,7 @@ document.write("Last Published: " + document.lastModified);
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JobConf.getOutputPath()</a>, and the framework will promote them
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JobConf.getOutputPath()</a>, and the framework will promote them
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similarly for succesful task-attempts, thus eliminating the need to
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similarly for succesful task-attempts, thus eliminating the need to
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pick unique paths per task-attempt.</p>
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pick unique paths per task-attempt.</p>
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-<a name="N109A4"></a><a name="RecordWriter"></a>
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+<a name="N10A19"></a><a name="RecordWriter"></a>
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<h4>RecordWriter</h4>
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<h4>RecordWriter</h4>
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<p>
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<p>
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<a href="api/org/apache/hadoop/mapred/RecordWriter.html">
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<a href="api/org/apache/hadoop/mapred/RecordWriter.html">
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@@ -1665,9 +1728,9 @@ document.write("Last Published: " + document.lastModified);
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pairs to an output file.</p>
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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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<p>RecordWriter implementations write the job outputs to the
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<span class="codefrag">FileSystem</span>.</p>
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<span class="codefrag">FileSystem</span>.</p>
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-<a name="N109BB"></a><a name="Other+Useful+Features"></a>
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+<a name="N10A30"></a><a name="Other+Useful+Features"></a>
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<h3 class="h4">Other Useful Features</h3>
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<h3 class="h4">Other Useful Features</h3>
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-<a name="N109C1"></a><a name="Counters"></a>
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+<a name="N10A36"></a><a name="Counters"></a>
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<h4>Counters</h4>
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<h4>Counters</h4>
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<p>
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<p>
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<span class="codefrag">Counters</span> represent global counters, defined either by
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<span class="codefrag">Counters</span> represent global counters, defined either by
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@@ -1681,7 +1744,7 @@ document.write("Last Published: " + document.lastModified);
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Reporter.incrCounter(Enum, long)</a> in the <span class="codefrag">map</span> and/or
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Reporter.incrCounter(Enum, long)</a> 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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<span class="codefrag">reduce</span> methods. These counters are then globally
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aggregated by the framework.</p>
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aggregated by the framework.</p>
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-<a name="N109EC"></a><a name="DistributedCache"></a>
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+<a name="N10A61"></a><a name="DistributedCache"></a>
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<h4>DistributedCache</h4>
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<h4>DistributedCache</h4>
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<p>
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<p>
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<a href="api/org/apache/hadoop/filecache/DistributedCache.html">
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<a href="api/org/apache/hadoop/filecache/DistributedCache.html">
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@@ -1701,19 +1764,20 @@ document.write("Last Published: " + document.lastModified);
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per job and the ability to cache archives which are un-archived on
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per job and the ability to cache archives which are un-archived on
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the slaves.</p>
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the slaves.</p>
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<p>
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<p>
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-<span class="codefrag">DistributedCache</span> can be used to distribute simple,
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- read-only data/text files and more complex types such as archives and
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- jars. Archives (zip files) are <em>un-archived</em> at the slave nodes.
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- Jars maybe be optionally added to the classpath of the tasks, a
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- rudimentary <em>software distribution</em> mechanism. Files have
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- <em>execution permissions</em> set. Optionally users can also direct the
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- <span class="codefrag">DistributedCache</span> to <em>symlink</em> the cached file(s)
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- into the working directory of the task.</p>
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-<p>
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<span class="codefrag">DistributedCache</span> tracks the modification timestamps of
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<span class="codefrag">DistributedCache</span> tracks the modification timestamps of
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the cached files. Clearly the cache files should not be modified by
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the cached files. Clearly the cache files should not be modified by
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the application or externally while the job is executing.</p>
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the application or externally while the job is executing.</p>
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-<a name="N10A26"></a><a name="Tool"></a>
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+<p>
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+<span class="codefrag">DistributedCache</span> can be used to distribute simple,
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+ read-only data/text files and more complex types such as archives and
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+ jars. Archives (zip files) are <em>un-archived</em> at the slave nodes.
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+ Optionally users can also direct the <span class="codefrag">DistributedCache</span> to
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+ <em>symlink</em> the cached file(s) into the <span class="codefrag">current working
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+ directory</span> of the task via the
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+ <a href="api/org/apache/hadoop/filecache/DistributedCache.html#createSymlink(org.apache.hadoop.conf.Configuration)">
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+ DistributedCache.createSymlink(Path, Configuration)</a> api. Files
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+ have <em>execution permissions</em> set.</p>
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+<a name="N10A9F"></a><a name="Tool"></a>
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<h4>Tool</h4>
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<h4>Tool</h4>
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<p>The <a href="api/org/apache/hadoop/util/Tool.html">Tool</a>
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<p>The <a href="api/org/apache/hadoop/util/Tool.html">Tool</a>
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interface supports the handling of generic Hadoop command-line options.
|
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interface supports the handling of generic Hadoop command-line options.
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@@ -1753,7 +1817,7 @@ document.write("Last Published: " + document.lastModified);
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</span>
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</span>
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</p>
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</p>
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-<a name="N10A58"></a><a name="IsolationRunner"></a>
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+<a name="N10AD1"></a><a name="IsolationRunner"></a>
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<h4>IsolationRunner</h4>
|
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<h4>IsolationRunner</h4>
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<p>
|
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<p>
|
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<a href="api/org/apache/hadoop/mapred/IsolationRunner.html">
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<a href="api/org/apache/hadoop/mapred/IsolationRunner.html">
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@@ -1777,13 +1841,13 @@ document.write("Last Published: " + document.lastModified);
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<p>
|
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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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<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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jvm, which can be in the debugger, over precisely the same input.</p>
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-<a name="N10A8B"></a><a name="JobControl"></a>
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+<a name="N10B04"></a><a name="JobControl"></a>
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<h4>JobControl</h4>
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<h4>JobControl</h4>
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<p>
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<p>
|
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<a href="api/org/apache/hadoop/mapred/jobcontrol/package-summary.html">
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<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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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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and their dependencies.</p>
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-<a name="N10A98"></a><a name="Data+Compression"></a>
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+<a name="N10B11"></a><a name="Data+Compression"></a>
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<h4>Data Compression</h4>
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<h4>Data Compression</h4>
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<p>Hadoop Map-Reduce provides facilities for the application-writer to
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<p>Hadoop Map-Reduce provides facilities for the application-writer to
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specify compression for both intermediate map-outputs and the
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specify compression for both intermediate map-outputs and the
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@@ -1797,7 +1861,7 @@ 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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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
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Java libraries (lzo). More details on their usage and availability are
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available <a href="native_libraries.html">here</a>.</p>
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available <a href="native_libraries.html">here</a>.</p>
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-<a name="N10AB8"></a><a name="Intermediate+Outputs"></a>
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+<a name="N10B31"></a><a name="Intermediate+Outputs"></a>
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<h5>Intermediate Outputs</h5>
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<h5>Intermediate Outputs</h5>
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<p>Applications can control compression of intermediate map-outputs
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<p>Applications can control compression of intermediate map-outputs
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via the
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via the
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@@ -1818,7 +1882,7 @@ document.write("Last Published: " + document.lastModified);
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<a href="api/org/apache/hadoop/mapred/JobConf.html#setMapOutputCompressionType(org.apache.hadoop.io.SequenceFile.CompressionType)">
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<a href="api/org/apache/hadoop/mapred/JobConf.html#setMapOutputCompressionType(org.apache.hadoop.io.SequenceFile.CompressionType)">
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JobConf.setMapOutputCompressionType(SequenceFile.CompressionType)</a>
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JobConf.setMapOutputCompressionType(SequenceFile.CompressionType)</a>
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api.</p>
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api.</p>
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-<a name="N10AE4"></a><a name="Job+Outputs"></a>
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+<a name="N10B5D"></a><a name="Job+Outputs"></a>
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<h5>Job Outputs</h5>
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<h5>Job Outputs</h5>
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<p>Applications can control compression of job-outputs via the
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<p>Applications can control compression of job-outputs via the
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<a href="api/org/apache/hadoop/mapred/OutputFormatBase.html#setCompressOutput(org.apache.hadoop.mapred.JobConf,%20boolean)">
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<a href="api/org/apache/hadoop/mapred/OutputFormatBase.html#setCompressOutput(org.apache.hadoop.mapred.JobConf,%20boolean)">
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@@ -1838,12 +1902,12 @@ document.write("Last Published: " + document.lastModified);
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</div>
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</div>
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-<a name="N10B13"></a><a name="Example%3A+WordCount+v2.0"></a>
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+<a name="N10B8C"></a><a name="Example%3A+WordCount+v2.0"></a>
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<h2 class="h3">Example: WordCount v2.0</h2>
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<h2 class="h3">Example: WordCount v2.0</h2>
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<div class="section">
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<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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<p>Here is a more complete <span class="codefrag">WordCount</span> which uses many of the
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features provided by the Map-Reduce framework we discussed so far:</p>
|
|
features provided by the Map-Reduce framework we discussed so far:</p>
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-<a name="N10B1F"></a><a name="Source+Code-N10B1F"></a>
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+<a name="N10B98"></a><a name="Source+Code-N10B98"></a>
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<h3 class="h4">Source Code</h3>
|
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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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<table class="ForrestTable" cellspacing="1" cellpadding="4">
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@@ -3021,7 +3085,7 @@ document.write("Last Published: " + document.lastModified);
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</tr>
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</tr>
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</table>
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</table>
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-<a name="N11251"></a><a name="Sample+Runs"></a>
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+<a name="N112CA"></a><a name="Sample+Runs"></a>
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|
<h3 class="h4">Sample Runs</h3>
|
|
<h3 class="h4">Sample Runs</h3>
|
|
<p>Sample text-files as input:</p>
|
|
<p>Sample text-files as input:</p>
|
|
<p>
|
|
<p>
|
|
@@ -3186,7 +3250,7 @@ document.write("Last Published: " + document.lastModified);
|
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<br>
|
|
<br>
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</p>
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</p>
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-<a name="N11321"></a><a name="Salient+Points"></a>
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+<a name="N1139A"></a><a name="Salient+Points"></a>
|
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<h3 class="h4">Salient Points</h3>
|
|
<h3 class="h4">Salient Points</h3>
|
|
<p>The second version of <span class="codefrag">WordCount</span> improves upon the
|
|
<p>The second version of <span class="codefrag">WordCount</span> improves upon the
|
|
previous one by using some features offered by the Map-Reduce framework:
|
|
previous one by using some features offered by the Map-Reduce framework:
|