src/java/overview.html - hadoop - Git at Google

 <html>
 <head>
    <title>Hadoop</title>
 </head>
 <body>

 Hadoop is a distributed computing platform.

 <p>Hadoop primarily consists of a distributed filesystem (DFS, in <a
 href="org/apache/hadoop/dfs/package-summary.html">org.apache.hadoop.dfs</a>)
 and an implementation of a MapReduce distributed data processor (in <a
 href="org/apache/hadoop/mapred/package-summary.html">org.apache.hadoop.mapred
 </a>).</p>

 <h2>Requirements</h2>

 <ol>

 <li>Java 1.5.x, preferably from <a
  href="http://java.sun.com/j2se/downloads.html">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.  On Ubuntu, this may done
 with <br><tt>sudo apt-get install ssh</tt></li>

 <li>rsync must be installed to use Hadoop's scripts to manage remote
 Hadoop installations.  On Ubuntu, this may done with <br><tt>sudo
 apt-get install rsync</tt>.</li>

 <li>On Win32, <a href="http://www.cygwin.com/">cygwin</a>, for shell
 support.  To use Subversion on Win32, select the subversion package
 when you install, in the "Devel" category.  Distributed operation has
 not been well tested on Win32, so this should primarily be considered
 a development platform at this point, not a production platform.</li>

 </ol>

 <h2>Getting Started</h2>

 <p>First, you need to get a copy of the Hadoop code.</p>

 <p>You can download a nightly build from <a
 href="http://cvs.apache.org/dist/lucene/hadoop/nightly/">http://cvs.apache.org/dist/lucene/hadoop/nightly/</a>.
 Unpack the release and connect to its top-level directory.</p>

 <p>Or, check out the code from <a
 href="http://lucene.apache.org/hadoop/version_control.html">subversion</a>
 and build it with <a href="http://ant.apache.org/">Ant</a>.</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 {@link org.apache.hadoop.dfs.NameNode} (Distributed Filesystem
 master) host and port.  This is specified with the configuration
 property <tt><a
 href="../hadoop-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="../hadoop-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 conf/hadoop-site.xml:

 <xmp><configuration>

   <property>
     <name>fs.default.name</name>
     <value>localhost:9000</value>
   </property>

   <property>
     <name>mapred.job.tracker</name>
     <value>localhost:9001</value>
   </property>

   <property>
     <name>dfs.replication</name>
     <value>1</value>
   </property>

 </configuration></xmp>

 <p>(We also set the DFS 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 dfs -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 dfs -get output output
 cat output/*
 </tt>

 <p>When you're done, stop the daemons with:</p>

 <p><tt>bin/stop-all.sh</tt></p>

 <h2>Fully-distributed operation</h2>

 <p>Distributed operation is just like the pseudo-distributed operation
 described above, except:</p>

 <ol>

 <li>Specify hostname or IP address of the master server in the values
 for <tt><a
 href="../hadoop-default.html#fs.default.name">fs.default.name</a></tt>
 and <tt><a
 href="../hadoop-default.html#mapred.job.tracker">mapred.job.tracker</a></tt>
 in <tt>conf/hadoop-site.xml</tt>.  These are specified as
 <tt><em>host</em>:<em>port</em></tt> pairs.</li>

 <li>Specify directories for <tt><a
 href="../hadoop-default.html#dfs.name.dir">dfs.name.dir</a></tt> and
 <tt><a
 href="../hadoop-default.html#dfs.data.dir">dfs.data.dir</a></tt> in
 <tt>conf/hadoop-site.xml</tt>.  These are 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
 devices.</li>

 <li>Specify <tt><a
 href="../hadoop-default.html#mapred.local.dir">mapred.local.dir</a></tt>
 in <tt>conf/hadoop-site.xml</tt>.  This determines where temporary
 MapReduce data is written.  It also may be a list of directories.</li>

 <li>Specify <tt><a
 href="../hadoop-default.html#mapred.map.tasks">mapred.map.tasks</a></tt>
 and <tt><a
 href="../hadoop-default.html#mapred.reduce.tasks">mapred.reduce.tasks</a></tt>
 in <tt>conf/mapred-default.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>

 <li>List all slave hostnames or IP addresses in your
 <tt>conf/slaves</tt> file, one per line.</li>

 </ol>

 </body>
 </html>
	<html>
	<head>
	<title>Hadoop</title>
	</head>
	<body>

	Hadoop is a distributed computing platform.

	<p>Hadoop primarily consists of a distributed filesystem (DFS, in <a
	href="org/apache/hadoop/dfs/package-summary.html">org.apache.hadoop.dfs</a>)
	and an implementation of a MapReduce distributed data processor (in <a
	href="org/apache/hadoop/mapred/package-summary.html">org.apache.hadoop.mapred
	</a>).</p>

	<h2>Requirements</h2>

	<ol>

	<li>Java 1.5.x, preferably from <a
	href="http://java.sun.com/j2se/downloads.html">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. On Ubuntu, this may done
	with <br><tt>sudo apt-get install ssh</tt></li>

	<li>rsync must be installed to use Hadoop's scripts to manage remote
	Hadoop installations. On Ubuntu, this may done with <br><tt>sudo
	apt-get install rsync</tt>.</li>

	<li>On Win32, <a href="http://www.cygwin.com/">cygwin</a>, for shell
	support. To use Subversion on Win32, select the subversion package
	when you install, in the "Devel" category. Distributed operation has
	not been well tested on Win32, so this should primarily be considered
	a development platform at this point, not a production platform.</li>

	</ol>

	<h2>Getting Started</h2>

	<p>First, you need to get a copy of the Hadoop code.</p>

	<p>You can download a nightly build from <a
	href="http://cvs.apache.org/dist/lucene/hadoop/nightly/">http://cvs.apache.org/dist/lucene/hadoop/nightly/</a>.
	Unpack the release and connect to its top-level directory.</p>

	<p>Or, check out the code from <a
	href="http://lucene.apache.org/hadoop/version_control.html">subversion</a>
	and build it with <a href="http://ant.apache.org/">Ant</a>.</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 {@link org.apache.hadoop.dfs.NameNode} (Distributed Filesystem
	master) host and port. This is specified with the configuration
	property <tt><a
	href="../hadoop-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="../hadoop-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 conf/hadoop-site.xml:

	<xmp><configuration>

	<property>
	<name>fs.default.name</name>
	<value>localhost:9000</value>
	</property>

	<property>
	<name>mapred.job.tracker</name>
	<value>localhost:9001</value>
	</property>

	<property>
	<name>dfs.replication</name>
	<value>1</value>
	</property>

	</configuration></xmp>

	<p>(We also set the DFS 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 dfs -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 dfs -get output output
	cat output/*
	</tt>

	<p>When you're done, stop the daemons with:</p>

	<p><tt>bin/stop-all.sh</tt></p>

	<h2>Fully-distributed operation</h2>

	<p>Distributed operation is just like the pseudo-distributed operation
	described above, except:</p>

	<ol>

	<li>Specify hostname or IP address of the master server in the values
	for <tt><a
	href="../hadoop-default.html#fs.default.name">fs.default.name</a></tt>
	and <tt><a
	href="../hadoop-default.html#mapred.job.tracker">mapred.job.tracker</a></tt>
	in <tt>conf/hadoop-site.xml</tt>. These are specified as
	<tt><em>host</em>:<em>port</em></tt> pairs.</li>

	<li>Specify directories for <tt><a
	href="../hadoop-default.html#dfs.name.dir">dfs.name.dir</a></tt> and
	<tt><a
	href="../hadoop-default.html#dfs.data.dir">dfs.data.dir</a></tt> in
	<tt>conf/hadoop-site.xml</tt>. These are 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
	devices.</li>

	<li>Specify <tt><a
	href="../hadoop-default.html#mapred.local.dir">mapred.local.dir</a></tt>
	in <tt>conf/hadoop-site.xml</tt>. This determines where temporary
	MapReduce data is written. It also may be a list of directories.</li>

	<li>Specify <tt><a
	href="../hadoop-default.html#mapred.map.tasks">mapred.map.tasks</a></tt>
	and <tt><a
	href="../hadoop-default.html#mapred.reduce.tasks">mapred.reduce.tasks</a></tt>
	in <tt>conf/mapred-default.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>

	<li>List all slave hostnames or IP addresses in your
	<tt>conf/slaves</tt> file, one per line.</li>

	</ol>

	</body>
	</html>