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| <head> |
| <title>Hadoop</title> |
| </head> |
| <body> |
| |
| Hadoop is a distributed computing platform. |
| |
| <p>Hadoop primarily consists of the <a |
| href="org/apache/hadoop/hdfs/package-summary.html">Hadoop Distributed FileSystem |
| (HDFS)</a> and an |
| implementation of the <a href="org/apache/hadoop/mapred/package-summary.html"> |
| Map-Reduce</a> programming paradigm.</p> |
| |
| |
| <p>Hadoop is a software framework that lets one easily write and run applications |
| that process vast amounts of data. Here's what makes Hadoop especially useful:</p> |
| <ul> |
| <li> |
| <b>Scalable</b>: Hadoop can reliably store and process petabytes. |
| </li> |
| <li> |
| <b>Economical</b>: It distributes the data and processing across clusters |
| of commonly available computers. These clusters can number into the thousands |
| of nodes. |
| </li> |
| <li> |
| <b>Efficient</b>: By distributing the data, Hadoop can process it in parallel |
| on the nodes where the data is located. This makes it extremely rapid. |
| </li> |
| <li> |
| <b>Reliable</b>: Hadoop automatically maintains multiple copies of data and |
| automatically redeploys computing tasks based on failures. |
| </li> |
| </ul> |
| |
| <h2>Requirements</h2> |
| |
| <h3>Platforms</h3> |
| |
| <ul> |
| <li> |
| Hadoop was been demonstrated on GNU/Linux clusters with 2000 nodes. |
| </li> |
| <li> |
| Win32 is supported as a <i>development</i> platform. Distributed operation |
| has not been well tested on Win32, so this is not a <i>production</i> |
| platform. |
| </li> |
| </ul> |
| |
| <h3>Requisite Software</h3> |
| |
| <ol> |
| <li> |
| Java 1.6.x, preferably from |
| <a href="http://java.sun.com/javase/downloads/">Sun</a>. |
| Set <tt>JAVA_HOME</tt> to the root of your Java installation. |
| </li> |
| <li> |
| ssh must be installed and sshd must be running to use Hadoop's |
| scripts to manage remote Hadoop daemons. |
| </li> |
| <li> |
| rsync may be installed to use Hadoop's scripts to manage remote |
| Hadoop installations. |
| </li> |
| </ol> |
| |
| <h4>Additional requirements for Windows</h4> |
| |
| <ol> |
| <li> |
| <a href="http://www.cygwin.com/">Cygwin</a> - Required for shell support in |
| addition to the required software above. |
| </li> |
| </ol> |
| |
| <h3>Installing Required Software</h3> |
| |
| <p>If your platform does not have the required software listed above, you |
| will have to install it.</p> |
| |
| <p>For example on Ubuntu Linux:</p> |
| <p><blockquote><pre> |
| $ sudo apt-get install ssh<br> |
| $ sudo apt-get install rsync<br> |
| </pre></blockquote></p> |
| |
| <p>On Windows, if you did not install the required software when you |
| installed cygwin, start the cygwin installer and select the packages:</p> |
| <ul> |
| <li>openssh - the "Net" category</li> |
| <li>rsync - the "Net" category</li> |
| </ul> |
| |
| <h2>Getting Started</h2> |
| |
| <p>First, you need to get a copy of the Hadoop code.</p> |
| |
| <p>Edit the file <tt>conf/hadoop-env.sh</tt> to define at least |
| <tt>JAVA_HOME</tt>.</p> |
| |
| <p>Try the following command:</p> |
| <tt>bin/hadoop</tt> |
| <p>This will display the documentation for the Hadoop command script.</p> |
| |
| <h2>Standalone operation</h2> |
| |
| <p>By default, Hadoop is configured to run things in a non-distributed |
| mode, as a single Java process. This is useful for debugging, and can |
| be demonstrated as follows:</p> |
| <tt> |
| mkdir input<br> |
| cp conf/*.xml input<br> |
| bin/hadoop jar hadoop-examples-*.jar grep input output 'dfs[a-z.]+'<br> |
| cat output/* |
| </tt> |
| <p>This will display counts for each match of the <a |
| href="http://java.sun.com/j2se/1.4.2/docs/api/java/util/regex/Pattern.html"> |
| regular expression.</a></p> |
| |
| <p>Note that input is specified as a <em>directory</em> containing input |
| files and that output is also specified as a directory where parts are |
| written.</p> |
| |
| <h2>Distributed operation</h2> |
| |
| To configure Hadoop for distributed operation you must specify the |
| following: |
| |
| <ol> |
| |
| <li>The NameNode (Distributed Filesystem master) host. This is |
| specified with the configuration property <tt><a |
| href="../core-default.html#fs.default.name">fs.default.name</a></tt>. |
| </li> |
| |
| <li>The {@link org.apache.hadoop.mapred.JobTracker} (MapReduce master) |
| host and port. This is specified with the configuration property |
| <tt><a |
| href="../mapred-default.html#mapred.job.tracker">mapred.job.tracker</a></tt>. |
| </li> |
| |
| <li>A <em>slaves</em> file that lists the names of all the hosts in |
| the cluster. The default slaves file is <tt>conf/slaves</tt>. |
| |
| </ol> |
| |
| <h3>Pseudo-distributed configuration</h3> |
| |
| You can in fact run everything on a single host. To run things this |
| way, put the following in: |
| <br/> |
| <br/> |
| conf/core-site.xml: |
| <xmp><configuration> |
| |
| <property> |
| <name>fs.default.name</name> |
| <value>hdfs://localhost/</value> |
| </property> |
| |
| </configuration></xmp> |
| |
| conf/hdfs-site.xml: |
| <xmp><configuration> |
| |
| <property> |
| <name>dfs.replication</name> |
| <value>1</value> |
| </property> |
| |
| </configuration></xmp> |
| |
| conf/mapred-site.xml: |
| <xmp><configuration> |
| |
| <property> |
| <name>mapred.job.tracker</name> |
| <value>localhost:9001</value> |
| </property> |
| |
| </configuration></xmp> |
| |
| <p>(We also set the HDFS replication level to 1 in order to |
| reduce warnings when running on a single node.)</p> |
| |
| <p>Now check that the command <br><tt>ssh localhost</tt><br> does not |
| require a password. If it does, execute the following commands:</p> |
| |
| <p><tt>ssh-keygen -t dsa -P '' -f ~/.ssh/id_dsa<br> |
| cat ~/.ssh/id_dsa.pub >> ~/.ssh/authorized_keys |
| </tt></p> |
| |
| <h3>Bootstrapping</h3> |
| |
| <p>A new distributed filesystem must be formatted with the following |
| command, run on the master node:</p> |
| |
| <p><tt>bin/hadoop namenode -format</tt></p> |
| |
| <p>The Hadoop daemons are started with the following command:</p> |
| |
| <p><tt>bin/start-all.sh</tt></p> |
| |
| <p>Daemon log output is written to the <tt>logs/</tt> directory.</p> |
| |
| <p>Input files are copied into the distributed filesystem as follows:</p> |
| |
| <p><tt>bin/hadoop fs -put input input</tt></p> |
| |
| <h3>Distributed execution</h3> |
| |
| <p>Things are run as before, but output must be copied locally to |
| examine it:</p> |
| |
| <tt> |
| bin/hadoop jar hadoop-examples-*.jar grep input output 'dfs[a-z.]+'<br> |
| bin/hadoop fs -get output output |
| cat output/* |
| </tt> |
| |
| <p>When you're done, stop the daemons with:</p> |
| |
| <p><tt>bin/stop-all.sh</tt></p> |
| |
| <h3>Fully-distributed operation</h3> |
| |
| <p>Fully distributed operation is just like the pseudo-distributed operation |
| described above, except, specify:</p> |
| |
| <ol> |
| |
| <li>The hostname or IP address of your master server in the value |
| for <tt><a |
| href="../core-default.html#fs.default.name">fs.default.name</a></tt>, |
| as <tt><em>hdfs://master.example.com/</em></tt> in <tt>conf/core-site.xml</tt>.</li> |
| |
| <li>The host and port of the your master server in the value |
| of <tt><a href="../mapred-default.html#mapred.job.tracker">mapred.job.tracker</a></tt> |
| as <tt><em>master.example.com</em>:<em>port</em></tt> in <tt>conf/mapred-site.xml</tt>.</li> |
| |
| <li>Directories for <tt><a |
| href="../hdfs-default.html#dfs.name.dir">dfs.name.dir</a></tt> and |
| <tt><a href="../hdfs-default.html#dfs.data.dir">dfs.data.dir</a> |
| in <tt>conf/hdfs-site.xml</tt>. |
| </tt>These are local directories used to hold distributed filesystem |
| data on the master node and slave nodes respectively. Note |
| that <tt>dfs.data.dir</tt> may contain a space- or comma-separated |
| list of directory names, so that data may be stored on multiple local |
| devices.</li> |
| |
| <li><tt><a href="../mapred-default.html#mapred.local.dir">mapred.local.dir</a></tt> |
| in <tt>conf/mapred-site.xml</tt>, the local directory where temporary |
| MapReduce data is stored. It also may be a list of directories.</li> |
| |
| <li><tt><a |
| href="../mapred-default.html#mapred.map.tasks">mapred.map.tasks</a></tt> |
| and <tt><a |
| href="../mapred-default.html#mapred.reduce.tasks">mapred.reduce.tasks</a></tt> |
| in <tt>conf/mapred-site.xml</tt>. |
| As a rule of thumb, use 10x the |
| number of slave processors for <tt>mapred.map.tasks</tt>, and 2x the |
| number of slave processors for <tt>mapred.reduce.tasks</tt>.</li> |
| |
| </ol> |
| |
| <p>Finally, list all slave hostnames or IP addresses in your |
| <tt>conf/slaves</tt> file, one per line. Then format your filesystem |
| and start your cluster on your master node, as above. |
| |
| </body> |
| </html> |
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