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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="http://hadoop.apache.org/hdfs/">Hadoop Distributed FileSystem
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-(HDFS)</a> and an
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-implementation of the <a href="http://hadoop.apache.org/mapreduce/">
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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 has been demonstrated on GNU/Linux clusters with more than 4000 nodes.
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- </li>
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- <li>
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- Windows is also a supported 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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-<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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-<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 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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Brahma Reddy Battula