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+<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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+<html>
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+<!--
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+ Licensed to the Apache Software Foundation (ASF) under one or more
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+ contributor license agreements. See the NOTICE file distributed with
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+ this work for additional information regarding copyright ownership.
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+ The ASF licenses this file to You under the Apache License, Version 2.0
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+ (the "License"); you may not use this file except in compliance with
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+ the License. You may obtain a copy of the License at
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+
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+ http://www.apache.org/licenses/LICENSE-2.0
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+
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+ Unless required by applicable law or agreed to in writing, software
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+ distributed under the License is distributed on an "AS IS" BASIS,
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+ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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+ See the License for the specific language governing permissions and
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+ limitations under the License.
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+-->
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+<head>
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+ <title>Hadoop</title>
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+</head>
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+<body>
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+
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+Hadoop is a distributed computing platform.
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+
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+<p>Hadoop primarily consists of the <a
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+href="org/apache/hadoop/hdfs/package-summary.html">Hadoop Distributed FileSystem
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+(HDFS)</a> and an
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+implementation of the <a href="org/apache/hadoop/mapred/package-summary.html">
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+Map-Reduce</a> programming paradigm.</p>
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+
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+
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+<p>Hadoop is a software framework that lets one easily write and run applications
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+that process vast amounts of data. Here's what makes Hadoop especially useful:</p>
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+<ul>
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+ <li>
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+ <b>Scalable</b>: Hadoop can reliably store and process petabytes.
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+ </li>
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+ <li>
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+ <b>Economical</b>: It distributes the data and processing across clusters
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+ of commonly available computers. These clusters can number into the thousands
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+ of nodes.
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+ </li>
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+ <li>
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+ <b>Efficient</b>: By distributing the data, Hadoop can process it in parallel
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+ on the nodes where the data is located. This makes it extremely rapid.
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+ </li>
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+ <li>
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+ <b>Reliable</b>: Hadoop automatically maintains multiple copies of data and
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+ automatically redeploys computing tasks based on failures.
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+ </li>
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+</ul>
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+
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+<h2>Requirements</h2>
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+
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+<h3>Platforms</h3>
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+
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+<ul>
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+ <li>
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+ Hadoop was been demonstrated on GNU/Linux clusters with 2000 nodes.
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+ </li>
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+ <li>
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+ Win32 is supported as a <i>development</i> platform. Distributed operation
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+ has not been well tested on Win32, so this is not a <i>production</i>
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+ platform.
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+ </li>
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+</ul>
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+
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+<h3>Requisite Software</h3>
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+
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+<ol>
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+ <li>
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+ Java 1.6.x, preferably from
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+ <a href="http://java.sun.com/javase/downloads/">Sun</a>.
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+ Set <tt>JAVA_HOME</tt> to the root of your Java installation.
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+ </li>
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+ <li>
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+ ssh must be installed and sshd must be running to use Hadoop's
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+ scripts to manage remote Hadoop daemons.
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+ </li>
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+ <li>
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+ rsync may be installed to use Hadoop's scripts to manage remote
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+ Hadoop installations.
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+ </li>
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+</ol>
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+
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+<h4>Additional requirements for Windows</h4>
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+
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+<ol>
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+ <li>
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+ <a href="http://www.cygwin.com/">Cygwin</a> - Required for shell support in
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+ addition to the required software above.
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+ </li>
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+</ol>
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+
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+<h3>Installing Required Software</h3>
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+
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+<p>If your platform does not have the required software listed above, you
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+will have to install it.</p>
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+
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+<p>For example on Ubuntu Linux:</p>
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+<p><blockquote><pre>
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+$ sudo apt-get install ssh<br>
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+$ sudo apt-get install rsync<br>
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+</pre></blockquote></p>
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+
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+<p>On Windows, if you did not install the required software when you
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+installed cygwin, start the cygwin installer and select the packages:</p>
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+<ul>
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+ <li>openssh - the "Net" category</li>
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+ <li>rsync - the "Net" category</li>
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+</ul>
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+
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+<h2>Getting Started</h2>
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+
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+<p>First, you need to get a copy of the Hadoop code.</p>
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+
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+<p>Edit the file <tt>conf/hadoop-env.sh</tt> to define at least
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+<tt>JAVA_HOME</tt>.</p>
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+
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+<p>Try the following command:</p>
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+<tt>bin/hadoop</tt>
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+<p>This will display the documentation for the Hadoop command script.</p>
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+
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+<h2>Standalone operation</h2>
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+
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+<p>By default, Hadoop is configured to run things in a non-distributed
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+mode, as a single Java process. This is useful for debugging, and can
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+be demonstrated as follows:</p>
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+<tt>
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+mkdir input<br>
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+cp conf/*.xml input<br>
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+bin/hadoop jar hadoop-*-examples.jar grep input output 'dfs[a-z.]+'<br>
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+cat output/*
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+</tt>
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+<p>This will display counts for each match of the <a
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+href="http://java.sun.com/j2se/1.4.2/docs/api/java/util/regex/Pattern.html">
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+regular expression.</a></p>
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+
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+<p>Note that input is specified as a <em>directory</em> containing input
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+files and that output is also specified as a directory where parts are
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+written.</p>
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+
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+<h2>Distributed operation</h2>
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+
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+To configure Hadoop for distributed operation you must specify the
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+following:
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+
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+<ol>
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+
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+<li>The NameNode (Distributed Filesystem master) host. This is
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+specified with the configuration property <tt><a
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+ href="../core-default.html#fs.default.name">fs.default.name</a></tt>.
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+</li>
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+
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+<li>The {@link org.apache.hadoop.mapred.JobTracker} (MapReduce master)
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+host and port. This is specified with the configuration property
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+<tt><a
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+href="../mapred-default.html#mapred.job.tracker">mapred.job.tracker</a></tt>.
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+</li>
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+
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+<li>A <em>slaves</em> file that lists the names of all the hosts in
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+the cluster. The default slaves file is <tt>conf/slaves</tt>.
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+
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+</ol>
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+
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+<h3>Pseudo-distributed configuration</h3>
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+
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+You can in fact run everything on a single host. To run things this
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+way, put the following in:
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+<br/>
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+<br/>
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+conf/core-site.xml:
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+<xmp><configuration>
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+
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+ <property>
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+ <name>fs.default.name</name>
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+ <value>hdfs://localhost/</value>
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+ </property>
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+
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+</configuration></xmp>
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+
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+conf/hdfs-site.xml:
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+<xmp><configuration>
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+
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+ <property>
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+ <name>dfs.replication</name>
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+ <value>1</value>
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+ </property>
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+
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+</configuration></xmp>
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+
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+conf/mapred-site.xml:
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+<xmp><configuration>
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+
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+ <property>
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+ <name>mapred.job.tracker</name>
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+ <value>localhost:9001</value>
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+ </property>
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+
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+</configuration></xmp>
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+
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+<p>(We also set the HDFS replication level to 1 in order to
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+reduce warnings when running on a single node.)</p>
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+
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+<p>Now check that the command <br><tt>ssh localhost</tt><br> does not
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+require a password. If it does, execute the following commands:</p>
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+
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+<p><tt>ssh-keygen -t dsa -P '' -f ~/.ssh/id_dsa<br>
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+cat ~/.ssh/id_dsa.pub >> ~/.ssh/authorized_keys
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+</tt></p>
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+
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+<h3>Bootstrapping</h3>
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+
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+<p>A new distributed filesystem must be formatted with the following
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+command, run on the master node:</p>
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+
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+<p><tt>bin/hadoop namenode -format</tt></p>
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+
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+<p>The Hadoop daemons are started with the following command:</p>
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+
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+<p><tt>bin/start-all.sh</tt></p>
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+
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+<p>Daemon log output is written to the <tt>logs/</tt> directory.</p>
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+
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+<p>Input files are copied into the distributed filesystem as follows:</p>
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+
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+<p><tt>bin/hadoop fs -put input input</tt></p>
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+
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+<h3>Distributed execution</h3>
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+
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+<p>Things are run as before, but output must be copied locally to
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+examine it:</p>
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+
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+<tt>
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+bin/hadoop jar hadoop-*-examples.jar grep input output 'dfs[a-z.]+'<br>
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+bin/hadoop fs -get output output
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+cat output/*
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+</tt>
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+
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+<p>When you're done, stop the daemons with:</p>
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+
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+<p><tt>bin/stop-all.sh</tt></p>
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+
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+<h3>Fully-distributed operation</h3>
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+
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+<p>Fully distributed operation is just like the pseudo-distributed operation
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+described above, except, specify:</p>
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+
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+<ol>
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+
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+<li>The hostname or IP address of your master server in the value
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+for <tt><a
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+href="../core-default.html#fs.default.name">fs.default.name</a></tt>,
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+ as <tt><em>hdfs://master.example.com/</em></tt> in <tt>conf/core-site.xml</tt>.</li>
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+
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+<li>The host and port of the your master server in the value
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+of <tt><a href="../mapred-default.html#mapred.job.tracker">mapred.job.tracker</a></tt>
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+as <tt><em>master.example.com</em>:<em>port</em></tt> in <tt>conf/mapred-site.xml</tt>.</li>
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+
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+<li>Directories for <tt><a
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+href="../hdfs-default.html#dfs.name.dir">dfs.name.dir</a></tt> and
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+<tt><a href="../hdfs-default.html#dfs.data.dir">dfs.data.dir</a>
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+in <tt>conf/hdfs-site.xml</tt>.
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+</tt>These are local directories used to hold distributed filesystem
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+data on the master node and slave nodes respectively. Note
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+that <tt>dfs.data.dir</tt> may contain a space- or comma-separated
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+list of directory names, so that data may be stored on multiple local
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+devices.</li>
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+
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+<li><tt><a href="../mapred-default.html#mapred.local.dir">mapred.local.dir</a></tt>
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+ in <tt>conf/mapred-site.xml</tt>, the local directory where temporary
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+ MapReduce data is stored. It also may be a list of directories.</li>
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+
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+<li><tt><a
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+href="../mapred-default.html#mapred.map.tasks">mapred.map.tasks</a></tt>
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+and <tt><a
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+href="../mapred-default.html#mapred.reduce.tasks">mapred.reduce.tasks</a></tt>
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+in <tt>conf/mapred-site.xml</tt>.
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+As a rule of thumb, use 10x the
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+number of slave processors for <tt>mapred.map.tasks</tt>, and 2x the
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+number of slave processors for <tt>mapred.reduce.tasks</tt>.</li>
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+
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+</ol>
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+
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+<p>Finally, list all slave hostnames or IP addresses in your
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+<tt>conf/slaves</tt> file, one per line. Then format your filesystem
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+and start your cluster on your master node, as above.
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+
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+</body>
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+</html>
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+
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Giridharan Kesavan