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@@ -268,6 +268,9 @@ document.write("Last Published: " + document.lastModified);
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<a href="#Job+Output">Job Output</a>
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<ul class="minitoc">
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<li>
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+<a href="#OutputCommitter">OutputCommitter</a>
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+</li>
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+<li>
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<a href="#Task+Side-Effect+Files">Task Side-Effect Files</a>
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</li>
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<li>
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@@ -310,7 +313,7 @@ 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-N10E0A">Source Code</a>
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+<a href="#Source+Code-N10E46">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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@@ -1258,16 +1261,17 @@ document.write("Last Published: " + document.lastModified);
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<p>We will then discuss other core interfaces including
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<span class="codefrag">JobConf</span>, <span class="codefrag">JobClient</span>, <span class="codefrag">Partitioner</span>,
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<span class="codefrag">OutputCollector</span>, <span class="codefrag">Reporter</span>,
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- <span class="codefrag">InputFormat</span>, <span class="codefrag">OutputFormat</span> and others.</p>
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+ <span class="codefrag">InputFormat</span>, <span class="codefrag">OutputFormat</span>,
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+ <span class="codefrag">OutputCommitter</span> and others.</p>
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<p>Finally, we will wrap up by discussing some useful features of the
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framework such as the <span class="codefrag">DistributedCache</span>,
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<span class="codefrag">IsolationRunner</span> etc.</p>
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-<a name="N105FC"></a><a name="Payload"></a>
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+<a name="N105FF"></a><a name="Payload"></a>
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<h3 class="h4">Payload</h3>
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<p>Applications typically implement the <span class="codefrag">Mapper</span> and
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<span class="codefrag">Reducer</span> interfaces to provide the <span class="codefrag">map</span> and
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<span class="codefrag">reduce</span> methods. These form the core of the job.</p>
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-<a name="N10611"></a><a name="Mapper"></a>
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+<a name="N10614"></a><a name="Mapper"></a>
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<h4>Mapper</h4>
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<p>
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<a href="api/org/apache/hadoop/mapred/Mapper.html">
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@@ -1323,7 +1327,7 @@ document.write("Last Published: " + document.lastModified);
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<a href="api/org/apache/hadoop/io/compress/CompressionCodec.html">
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CompressionCodec</a> to be used via the <span class="codefrag">JobConf</span>.
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</p>
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-<a name="N10687"></a><a name="How+Many+Maps%3F"></a>
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+<a name="N1068A"></a><a name="How+Many+Maps%3F"></a>
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<h5>How Many Maps?</h5>
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<p>The number of maps is usually driven by the total size of the
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inputs, that is, the total number of blocks of the input files.</p>
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@@ -1336,7 +1340,7 @@ document.write("Last Published: " + document.lastModified);
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<a href="api/org/apache/hadoop/mapred/JobConf.html#setNumMapTasks(int)">
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setNumMapTasks(int)</a> (which only provides a hint to the framework)
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is used to set it even higher.</p>
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-<a name="N1069F"></a><a name="Reducer"></a>
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+<a name="N106A2"></a><a name="Reducer"></a>
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<h4>Reducer</h4>
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<p>
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<a href="api/org/apache/hadoop/mapred/Reducer.html">
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@@ -1359,18 +1363,18 @@ document.write("Last Published: " + document.lastModified);
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<p>
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<span class="codefrag">Reducer</span> has 3 primary phases: shuffle, sort and reduce.
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</p>
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-<a name="N106CF"></a><a name="Shuffle"></a>
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+<a name="N106D2"></a><a name="Shuffle"></a>
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<h5>Shuffle</h5>
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<p>Input to the <span class="codefrag">Reducer</span> is the sorted output of the
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mappers. In this phase the framework fetches the relevant partition
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of the output of all the mappers, via HTTP.</p>
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-<a name="N106DC"></a><a name="Sort"></a>
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+<a name="N106DF"></a><a name="Sort"></a>
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<h5>Sort</h5>
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<p>The framework groups <span class="codefrag">Reducer</span> inputs by keys (since
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different mappers may have output the same key) in this stage.</p>
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<p>The shuffle and sort phases occur simultaneously; while
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map-outputs are being fetched they are merged.</p>
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-<a name="N106EB"></a><a name="Secondary+Sort"></a>
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+<a name="N106EE"></a><a name="Secondary+Sort"></a>
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<h5>Secondary Sort</h5>
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<p>If equivalence rules for grouping the intermediate keys are
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required to be different from those for grouping keys before
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@@ -1381,7 +1385,7 @@ document.write("Last Published: " + document.lastModified);
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JobConf.setOutputKeyComparatorClass(Class)</a> can be used to
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control how intermediate keys are grouped, these can be used in
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conjunction to simulate <em>secondary sort on values</em>.</p>
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-<a name="N10704"></a><a name="Reduce"></a>
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+<a name="N10707"></a><a name="Reduce"></a>
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<h5>Reduce</h5>
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<p>In this phase the
|
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|
<a href="api/org/apache/hadoop/mapred/Reducer.html#reduce(K2, java.util.Iterator, org.apache.hadoop.mapred.OutputCollector, org.apache.hadoop.mapred.Reporter)">
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@@ -1397,7 +1401,7 @@ document.write("Last Published: " + document.lastModified);
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progress, set application-level status messages and update
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<span class="codefrag">Counters</span>, or just indicate that they are alive.</p>
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<p>The output of the <span class="codefrag">Reducer</span> is <em>not sorted</em>.</p>
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-<a name="N10732"></a><a name="How+Many+Reduces%3F"></a>
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+<a name="N10735"></a><a name="How+Many+Reduces%3F"></a>
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<h5>How Many Reduces?</h5>
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<p>The right number of reduces seems to be <span class="codefrag">0.95</span> or
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|
<span class="codefrag">1.75</span> multiplied by (<<em>no. of nodes</em>> *
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@@ -1412,7 +1416,7 @@ document.write("Last Published: " + document.lastModified);
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<p>The scaling factors above are slightly less than whole numbers to
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reserve a few reduce slots in the framework for speculative-tasks and
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failed tasks.</p>
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-<a name="N10757"></a><a name="Reducer+NONE"></a>
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|
+<a name="N1075A"></a><a name="Reducer+NONE"></a>
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|
|
<h5>Reducer NONE</h5>
|
|
|
<p>It is legal to set the number of reduce-tasks to <em>zero</em> if
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|
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no reduction is desired.</p>
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@@ -1422,7 +1426,7 @@ document.write("Last Published: " + document.lastModified);
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setOutputPath(Path)</a>. The framework does not sort the
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|
map-outputs before writing them out to the <span class="codefrag">FileSystem</span>.
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|
</p>
|
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|
-<a name="N10772"></a><a name="Partitioner"></a>
|
|
|
+<a name="N10775"></a><a name="Partitioner"></a>
|
|
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<h4>Partitioner</h4>
|
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|
<p>
|
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|
<a href="api/org/apache/hadoop/mapred/Partitioner.html">
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|
@@ -1436,7 +1440,7 @@ document.write("Last Published: " + document.lastModified);
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<p>
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|
|
<a href="api/org/apache/hadoop/mapred/lib/HashPartitioner.html">
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|
|
HashPartitioner</a> is the default <span class="codefrag">Partitioner</span>.</p>
|
|
|
-<a name="N10791"></a><a name="Reporter"></a>
|
|
|
+<a name="N10794"></a><a name="Reporter"></a>
|
|
|
<h4>Reporter</h4>
|
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|
<p>
|
|
|
<a href="api/org/apache/hadoop/mapred/Reporter.html">
|
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|
@@ -1455,7 +1459,7 @@ document.write("Last Published: " + document.lastModified);
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|
</p>
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|
<p>Applications can also update <span class="codefrag">Counters</span> using the
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|
|
<span class="codefrag">Reporter</span>.</p>
|
|
|
-<a name="N107BB"></a><a name="OutputCollector"></a>
|
|
|
+<a name="N107BE"></a><a name="OutputCollector"></a>
|
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|
<h4>OutputCollector</h4>
|
|
|
<p>
|
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|
<a href="api/org/apache/hadoop/mapred/OutputCollector.html">
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@@ -1466,7 +1470,7 @@ document.write("Last Published: " + document.lastModified);
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<p>Hadoop Map/Reduce comes bundled with a
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|
|
<a href="api/org/apache/hadoop/mapred/lib/package-summary.html">
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|
|
library</a> of generally useful mappers, reducers, and partitioners.</p>
|
|
|
-<a name="N107D6"></a><a name="Job+Configuration"></a>
|
|
|
+<a name="N107D9"></a><a name="Job+Configuration"></a>
|
|
|
<h3 class="h4">Job Configuration</h3>
|
|
|
<p>
|
|
|
<a href="api/org/apache/hadoop/mapred/JobConf.html">
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@@ -1498,8 +1502,9 @@ document.write("Last Published: " + document.lastModified);
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<p>
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|
|
<span class="codefrag">JobConf</span> is typically used to specify the
|
|
|
<span class="codefrag">Mapper</span>, combiner (if any), <span class="codefrag">Partitioner</span>,
|
|
|
- <span class="codefrag">Reducer</span>, <span class="codefrag">InputFormat</span> and
|
|
|
- <span class="codefrag">OutputFormat</span> implementations. <span class="codefrag">JobConf</span> also
|
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|
+ <span class="codefrag">Reducer</span>, <span class="codefrag">InputFormat</span>,
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|
+ <span class="codefrag">OutputFormat</span> and <span class="codefrag">OutputCommitter</span>
|
|
|
+ implementations. <span class="codefrag">JobConf</span> also
|
|
|
indicates the set of input files
|
|
|
(<a href="api/org/apache/hadoop/mapred/FileInputFormat.html#setInputPaths(org.apache.hadoop.mapred.JobConf,%20org.apache.hadoop.fs.Path[])">setInputPaths(JobConf, Path...)</a>
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|
|
/<a href="api/org/apache/hadoop/mapred/FileInputFormat.html#addInputPath(org.apache.hadoop.mapred.JobConf,%20org.apache.hadoop.fs.Path)">addInputPath(JobConf, Path)</a>)
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@@ -1524,7 +1529,7 @@ 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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|
|
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>
|
|
|
-<a name="N10868"></a><a name="Task+Execution+%26+Environment"></a>
|
|
|
+<a name="N1086E"></a><a name="Task+Execution+%26+Environment"></a>
|
|
|
<h3 class="h4">Task Execution & Environment</h3>
|
|
|
<p>The <span class="codefrag">TaskTracker</span> executes the <span class="codefrag">Mapper</span>/
|
|
|
<span class="codefrag">Reducer</span> <em>task</em> as a child process in a separate jvm.
|
|
|
@@ -1778,7 +1783,7 @@ 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>
|
|
|
</p>
|
|
|
-<a name="N10A1D"></a><a name="Job+Submission+and+Monitoring"></a>
|
|
|
+<a name="N10A23"></a><a name="Job+Submission+and+Monitoring"></a>
|
|
|
<h3 class="h4">Job Submission and Monitoring</h3>
|
|
|
<p>
|
|
|
<a href="api/org/apache/hadoop/mapred/JobClient.html">
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|
@@ -1839,7 +1844,7 @@ 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>
|
|
|
-<a name="N10A7D"></a><a name="Job+Control"></a>
|
|
|
+<a name="N10A83"></a><a name="Job+Control"></a>
|
|
|
<h4>Job Control</h4>
|
|
|
<p>Users may need to chain Map/Reduce jobs to accomplish complex
|
|
|
tasks which cannot be done via a single Map/Reduce job. This is fairly
|
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@@ -1875,7 +1880,7 @@ document.write("Last Published: " + document.lastModified);
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</li>
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|
</ul>
|
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|
-<a name="N10AA7"></a><a name="Job+Input"></a>
|
|
|
+<a name="N10AAD"></a><a name="Job+Input"></a>
|
|
|
<h3 class="h4">Job Input</h3>
|
|
|
<p>
|
|
|
<a href="api/org/apache/hadoop/mapred/InputFormat.html">
|
|
|
@@ -1923,7 +1928,7 @@ document.write("Last Published: " + document.lastModified);
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|
appropriate <span class="codefrag">CompressionCodec</span>. However, it must be noted that
|
|
|
compressed files with the above extensions cannot be <em>split</em> and
|
|
|
each compressed file is processed in its entirety by a single mapper.</p>
|
|
|
-<a name="N10B11"></a><a name="InputSplit"></a>
|
|
|
+<a name="N10B17"></a><a name="InputSplit"></a>
|
|
|
<h4>InputSplit</h4>
|
|
|
<p>
|
|
|
<a href="api/org/apache/hadoop/mapred/InputSplit.html">
|
|
|
@@ -1937,7 +1942,7 @@ document.write("Last Published: " + document.lastModified);
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|
FileSplit</a> is the default <span class="codefrag">InputSplit</span>. It sets
|
|
|
<span class="codefrag">map.input.file</span> to the path of the input file for the
|
|
|
logical split.</p>
|
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|
-<a name="N10B36"></a><a name="RecordReader"></a>
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|
+<a name="N10B3C"></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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@@ -1949,7 +1954,7 @@ 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="N10B59"></a><a name="Job+Output"></a>
|
|
|
+<a name="N10B5F"></a><a name="Job+Output"></a>
|
|
|
<h3 class="h4">Job Output</h3>
|
|
|
<p>
|
|
|
<a href="api/org/apache/hadoop/mapred/OutputFormat.html">
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|
|
@@ -1974,7 +1979,51 @@ document.write("Last Published: " + document.lastModified);
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<p>
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|
|
<span class="codefrag">TextOutputFormat</span> is the default
|
|
|
<span class="codefrag">OutputFormat</span>.</p>
|
|
|
-<a name="N10B82"></a><a name="Task+Side-Effect+Files"></a>
|
|
|
+<a name="N10B88"></a><a name="OutputCommitter"></a>
|
|
|
+<h4>OutputCommitter</h4>
|
|
|
+<p>
|
|
|
+<a href="api/org/apache/hadoop/mapred/OutputCommitter.html">
|
|
|
+ OutputCommitter</a> describes the commit of task output for a
|
|
|
+ Map/Reduce job.</p>
|
|
|
+<p>The Map/Reduce framework relies on the <span class="codefrag">OutputCommitter</span>
|
|
|
+ of the job to:</p>
|
|
|
+<ol>
|
|
|
+
|
|
|
+<li>
|
|
|
+ Setup the job during initialization. For example, create
|
|
|
+ the temporary output directory for the job during the
|
|
|
+ initialization of the job. The job client does the setup
|
|
|
+ for the job.
|
|
|
+ </li>
|
|
|
+
|
|
|
+<li>
|
|
|
+ Cleanup the job after the job completion. For example, remove the
|
|
|
+ temporary output directory after the job completion. A separate
|
|
|
+ task does the cleanupJob at the end of the job.
|
|
|
+ </li>
|
|
|
+
|
|
|
+<li>
|
|
|
+ Setup the task temporary output.
|
|
|
+ </li>
|
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|
+
|
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|
+<li>
|
|
|
+ Check whether a task needs a commit. This is to avoid the commit
|
|
|
+ procedure if a task does not need commit.
|
|
|
+ </li>
|
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|
+
|
|
|
+<li>
|
|
|
+ Commit of the task output.
|
|
|
+ </li>
|
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|
+
|
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|
+<li>
|
|
|
+ Discard the task commit.
|
|
|
+ </li>
|
|
|
+
|
|
|
+</ol>
|
|
|
+<p>
|
|
|
+<span class="codefrag">FileOutputCommitter</span> is the default
|
|
|
+ <span class="codefrag">OutputCommitter</span>.</p>
|
|
|
+<a name="N10BB8"></a><a name="Task+Side-Effect+Files"></a>
|
|
|
<h4>Task Side-Effect Files</h4>
|
|
|
<p>In some applications, component tasks need to create and/or write to
|
|
|
side-files, which differ from the actual job-output files.</p>
|
|
|
@@ -1985,7 +2034,9 @@ document.write("Last Published: " + document.lastModified);
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|
|
application-writer will have to pick unique names per task-attempt
|
|
|
(using the attemptid, say <span class="codefrag">attempt_200709221812_0001_m_000000_0</span>),
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|
|
not just per task.</p>
|
|
|
-<p>To avoid these issues the Map/Reduce framework maintains a special
|
|
|
+<p>To avoid these issues the Map/Reduce framework, when the
|
|
|
+ <span class="codefrag">OutputCommitter</span> is <span class="codefrag">FileOutputCommitter</span>,
|
|
|
+ maintains a special
|
|
|
<span class="codefrag">${mapred.output.dir}/_temporary/_${taskid}</span> sub-directory
|
|
|
accessible via <span class="codefrag">${mapred.work.output.dir}</span>
|
|
|
for each task-attempt on the <span class="codefrag">FileSystem</span> where the output
|
|
|
@@ -2013,7 +2064,7 @@ document.write("Last Published: " + document.lastModified);
|
|
|
<p>The entire discussion holds true for maps of jobs with
|
|
|
reducer=NONE (i.e. 0 reduces) since output of the map, in that case,
|
|
|
goes directly to HDFS.</p>
|
|
|
-<a name="N10BCA"></a><a name="RecordWriter"></a>
|
|
|
+<a name="N10C06"></a><a name="RecordWriter"></a>
|
|
|
<h4>RecordWriter</h4>
|
|
|
<p>
|
|
|
<a href="api/org/apache/hadoop/mapred/RecordWriter.html">
|
|
|
@@ -2021,9 +2072,9 @@ document.write("Last Published: " + document.lastModified);
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|
|
pairs to an output file.</p>
|
|
|
<p>RecordWriter implementations write the job outputs to the
|
|
|
<span class="codefrag">FileSystem</span>.</p>
|
|
|
-<a name="N10BE1"></a><a name="Other+Useful+Features"></a>
|
|
|
+<a name="N10C1D"></a><a name="Other+Useful+Features"></a>
|
|
|
<h3 class="h4">Other Useful Features</h3>
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|
-<a name="N10BE7"></a><a name="Counters"></a>
|
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|
+<a name="N10C23"></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
|
|
|
@@ -2040,7 +2091,7 @@ document.write("Last Published: " + document.lastModified);
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|
in the <span class="codefrag">map</span> and/or
|
|
|
<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="N10C16"></a><a name="DistributedCache"></a>
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+<a name="N10C52"></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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@@ -2111,7 +2162,7 @@ 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="N10C99"></a><a name="Tool"></a>
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+<a name="N10CD5"></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>
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|
interface supports the handling of generic Hadoop command-line options.
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@@ -2151,7 +2202,7 @@ document.write("Last Published: " + document.lastModified);
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</span>
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</p>
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-<a name="N10CCB"></a><a name="IsolationRunner"></a>
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+<a name="N10D07"></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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@@ -2175,7 +2226,7 @@ document.write("Last Published: " + document.lastModified);
|
|
|
<p>
|
|
|
<span class="codefrag">IsolationRunner</span> will run the failed task in a single
|
|
|
jvm, which can be in the debugger, over precisely the same input.</p>
|
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|
-<a name="N10CFE"></a><a name="Profiling"></a>
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+<a name="N10D3A"></a><a name="Profiling"></a>
|
|
|
<h4>Profiling</h4>
|
|
|
<p>Profiling is a utility to get a representative (2 or 3) sample
|
|
|
of built-in java profiler for a sample of maps and reduces. </p>
|
|
|
@@ -2208,7 +2259,7 @@ document.write("Last Published: " + document.lastModified);
|
|
|
<span class="codefrag">-agentlib:hprof=cpu=samples,heap=sites,force=n,thread=y,verbose=n,file=%s</span>
|
|
|
|
|
|
</p>
|
|
|
-<a name="N10D32"></a><a name="Debugging"></a>
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|
|
+<a name="N10D6E"></a><a name="Debugging"></a>
|
|
|
<h4>Debugging</h4>
|
|
|
<p>Map/Reduce framework provides a facility to run user-provided
|
|
|
scripts for debugging. When map/reduce task fails, user can run
|
|
|
@@ -2219,14 +2270,14 @@ document.write("Last Published: " + document.lastModified);
|
|
|
<p> In the following sections we discuss how to submit debug script
|
|
|
along with the job. For submitting debug script, first it has to
|
|
|
distributed. Then the script has to supplied in Configuration. </p>
|
|
|
-<a name="N10D3E"></a><a name="How+to+distribute+script+file%3A"></a>
|
|
|
+<a name="N10D7A"></a><a name="How+to+distribute+script+file%3A"></a>
|
|
|
<h5> How to distribute script file: </h5>
|
|
|
<p>
|
|
|
The user has to use
|
|
|
<a href="mapred_tutorial.html#DistributedCache">DistributedCache</a>
|
|
|
mechanism to <em>distribute</em> and <em>symlink</em> the
|
|
|
debug script file.</p>
|
|
|
-<a name="N10D52"></a><a name="How+to+submit+script%3A"></a>
|
|
|
+<a name="N10D8E"></a><a name="How+to+submit+script%3A"></a>
|
|
|
<h5> How to submit script: </h5>
|
|
|
<p> A quick way to submit debug script is to set values for the
|
|
|
properties "mapred.map.task.debug.script" and
|
|
|
@@ -2250,17 +2301,17 @@ document.write("Last Published: " + document.lastModified);
|
|
|
<span class="codefrag">$script $stdout $stderr $syslog $jobconf $program </span>
|
|
|
|
|
|
</p>
|
|
|
-<a name="N10D74"></a><a name="Default+Behavior%3A"></a>
|
|
|
+<a name="N10DB0"></a><a name="Default+Behavior%3A"></a>
|
|
|
<h5> Default Behavior: </h5>
|
|
|
<p> For pipes, a default script is run to process core dumps under
|
|
|
gdb, prints stack trace and gives info about running threads. </p>
|
|
|
-<a name="N10D7F"></a><a name="JobControl"></a>
|
|
|
+<a name="N10DBB"></a><a name="JobControl"></a>
|
|
|
<h4>JobControl</h4>
|
|
|
<p>
|
|
|
<a href="api/org/apache/hadoop/mapred/jobcontrol/package-summary.html">
|
|
|
JobControl</a> is a utility which encapsulates a set of Map/Reduce jobs
|
|
|
and their dependencies.</p>
|
|
|
-<a name="N10D8C"></a><a name="Data+Compression"></a>
|
|
|
+<a name="N10DC8"></a><a name="Data+Compression"></a>
|
|
|
<h4>Data Compression</h4>
|
|
|
<p>Hadoop Map/Reduce provides facilities for the application-writer to
|
|
|
specify compression for both intermediate map-outputs and the
|
|
|
@@ -2274,7 +2325,7 @@ document.write("Last Published: " + document.lastModified);
|
|
|
codecs for reasons of both performance (zlib) and non-availability of
|
|
|
Java libraries (lzo). More details on their usage and availability are
|
|
|
available <a href="native_libraries.html">here</a>.</p>
|
|
|
-<a name="N10DAC"></a><a name="Intermediate+Outputs"></a>
|
|
|
+<a name="N10DE8"></a><a name="Intermediate+Outputs"></a>
|
|
|
<h5>Intermediate Outputs</h5>
|
|
|
<p>Applications can control compression of intermediate map-outputs
|
|
|
via the
|
|
|
@@ -2283,7 +2334,7 @@ document.write("Last Published: " + document.lastModified);
|
|
|
<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>
|
|
|
-<a name="N10DC1"></a><a name="Job+Outputs"></a>
|
|
|
+<a name="N10DFD"></a><a name="Job+Outputs"></a>
|
|
|
<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)">
|
|
|
@@ -2303,7 +2354,7 @@ document.write("Last Published: " + document.lastModified);
|
|
|
</div>
|
|
|
|
|
|
|
|
|
-<a name="N10DF0"></a><a name="Example%3A+WordCount+v2.0"></a>
|
|
|
+<a name="N10E2C"></a><a name="Example%3A+WordCount+v2.0"></a>
|
|
|
<h2 class="h3">Example: WordCount v2.0</h2>
|
|
|
<div class="section">
|
|
|
<p>Here is a more complete <span class="codefrag">WordCount</span> which uses many of the
|
|
|
@@ -2313,7 +2364,7 @@ document.write("Last Published: " + document.lastModified);
|
|
|
<a href="quickstart.html#SingleNodeSetup">pseudo-distributed</a> or
|
|
|
<a href="quickstart.html#Fully-Distributed+Operation">fully-distributed</a>
|
|
|
Hadoop installation.</p>
|
|
|
-<a name="N10E0A"></a><a name="Source+Code-N10E0A"></a>
|
|
|
+<a name="N10E46"></a><a name="Source+Code-N10E46"></a>
|
|
|
<h3 class="h4">Source Code</h3>
|
|
|
<table class="ForrestTable" cellspacing="1" cellpadding="4">
|
|
|
|
|
|
@@ -3523,7 +3574,7 @@ document.write("Last Published: " + document.lastModified);
|
|
|
</tr>
|
|
|
|
|
|
</table>
|
|
|
-<a name="N1156C"></a><a name="Sample+Runs"></a>
|
|
|
+<a name="N115A8"></a><a name="Sample+Runs"></a>
|
|
|
<h3 class="h4">Sample Runs</h3>
|
|
|
<p>Sample text-files as input:</p>
|
|
|
<p>
|
|
|
@@ -3691,7 +3742,7 @@ document.write("Last Published: " + document.lastModified);
|
|
|
<br>
|
|
|
|
|
|
</p>
|
|
|
-<a name="N11640"></a><a name="Highlights"></a>
|
|
|
+<a name="N1167C"></a><a name="Highlights"></a>
|
|
|
<h3 class="h4">Highlights</h3>
|
|
|
<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:
|
Devaraj Das