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<h1>Native Hadoop Libraries</h1>
<div id="minitoc-area">
<ul class="minitoc">
<li>
<a href="#Purpose">Purpose</a>
</li>
<li>
<a href="#Components">Components</a>
</li>
<li>
<a href="#Usage">Usage</a>
</li>
<li>
<a href="#Supported+Platforms">Supported Platforms</a>
</li>
<li>
<a href="#Building+Native+Hadoop+Libraries">Building Native Hadoop Libraries</a>
<ul class="minitoc">
<li>
<a href="#Notes">Notes</a>
</li>
</ul>
</li>
<li>
<a href="#Loading+native+libraries+through+DistributedCache"> Loading native libraries through DistributedCache </a>
</li>
</ul>
</div>
  
    
<a name="N1000D"></a><a name="Purpose"></a>
<h2 class="h3">Purpose</h2>
<div class="section">
<p>Hadoop has native implementations of certain components for reasons of 
      both performance and non-availability of Java implementations. These 
      components are available in a single, dynamically-linked, native library. 
      On the *nix platform it is <em>libhadoop.so</em>. This document describes 
      the usage and details on how to build the native libraries.</p>
</div>
    
    
<a name="N1001A"></a><a name="Components"></a>
<h2 class="h3">Components</h2>
<div class="section">
<p>Hadoop currently has the following 
      <a href="api/org/apache/hadoop/io/compress/CompressionCodec.html">
      compression codecs</a> as the native components:</p>
<ul>
        
<li>
<a href="http://www.zlib.net/">zlib</a>
</li>
        
<li>
<a href="http://www.gzip.org/">gzip</a>
</li>
        
<li>
<a href="http://www.oberhumer.com/opensource/lzo/">lzo</a>
</li>
      
</ul>
<p>Of the above, the availability of native hadoop libraries is imperative 
      for the lzo and gzip compression codecs to work.</p>
</div>

    
<a name="N1003D"></a><a name="Usage"></a>
<h2 class="h3">Usage</h2>
<div class="section">
<p>It is fairly simple to use the native hadoop libraries:</p>
<ul>
        
<li>
          Take a look at the 
          <a href="#Supported+Platforms">supported platforms</a>.
        </li>
        
<li>
          Either <a href="http://hadoop.apache.org/core/releases.html#Download">download</a> the pre-built 
          32-bit i386-Linux native hadoop libraries (available as part of hadoop 
          distribution in <span class="codefrag">lib/native</span> directory) or 
          <a href="#Building+Native+Hadoop+Libraries">build</a> them yourself.
        </li>
        
<li>
          Make sure you have either or both of <strong>&gt;zlib-1.2</strong> and 
          <strong>&gt;lzo2.0</strong> packages for your platform installed; 
          depending on your needs.
        </li>
      
</ul>
<p>The <span class="codefrag">bin/hadoop</span> script ensures that the native hadoop 
      library is on the library path via the system property 
      <em>-Djava.library.path=&lt;path&gt;</em>.</p>
<p>To check everything went alright check the hadoop log files for:</p>
<p>
        
<span class="codefrag">
          DEBUG util.NativeCodeLoader - Trying to load the custom-built 
          native-hadoop library... 
        </span>
<br>
        
<span class="codefrag">
          INFO  util.NativeCodeLoader - Loaded the native-hadoop library
        </span>
      
</p>
<p>If something goes wrong, then:</p>
<p>
        
<span class="codefrag">
          INFO util.NativeCodeLoader - Unable to load native-hadoop library for 
          your platform... using builtin-java classes where applicable
        </span>
      
</p>
</div>
    
    
<a name="N10087"></a><a name="Supported+Platforms"></a>
<h2 class="h3">Supported Platforms</h2>
<div class="section">
<p>Hadoop native library is supported only on *nix platforms only.
      Unfortunately it is known not to work on <a href="http://www.cygwin.com/">Cygwin</a> 
      and <a href="http://www.apple.com/macosx">Mac OS X</a> and has mainly been used on the 
      GNU/Linux platform.</p>
<p>It has been tested on the following GNU/Linux distributions:</p>
<ul>
        
<li>
          
<a href="http://www.redhat.com/rhel/">RHEL4</a>/<a href="http://fedora.redhat.com/">Fedora</a>
        
</li>
        
<li>
<a href="http://www.ubuntu.com/">Ubuntu</a>
</li>
        
<li>
<a href="http://www.gentoo.org/">Gentoo</a>
</li>
      
</ul>
<p>On all the above platforms a 32/64 bit Hadoop native library will work 
      with a respective 32/64 bit jvm.</p>
</div>
    
    
<a name="N100B7"></a><a name="Building+Native+Hadoop+Libraries"></a>
<h2 class="h3">Building Native Hadoop Libraries</h2>
<div class="section">
<p>Hadoop native library is written in 
      <a href="http://en.wikipedia.org/wiki/ANSI_C">ANSI C</a> and built using 
      the GNU autotools-chain (autoconf, autoheader, automake, autoscan, libtool). 
      This means it should be straight-forward to build them on any platform with 
      a standards compliant C compiler and the GNU autotools-chain. 
      See <a href="#Supported+Platforms">supported platforms</a>.</p>
<p>In particular the various packages you would need on the target 
      platform are:</p>
<ul>
        
<li>
          C compiler (e.g. <a href="http://gcc.gnu.org/">GNU C Compiler</a>)
        </li>
        
<li>
          GNU Autools Chain: 
          <a href="http://www.gnu.org/software/autoconf/">autoconf</a>, 
          <a href="http://www.gnu.org/software/automake/">automake</a>, 
          <a href="http://www.gnu.org/software/libtool/">libtool</a>
        
</li>
        
<li> 
          zlib-development package (stable version &gt;= 1.2.0)
        </li>
        
<li> 
          lzo-development package (stable version &gt;= 2.0)
        </li> 
      
</ul>
<p>Once you have the pre-requisites use the standard <span class="codefrag">build.xml</span> 
      and pass along the <span class="codefrag">compile.native</span> flag (set to 
      <span class="codefrag">true</span>) to build the native hadoop library:</p>
<p>
<span class="codefrag">$ ant -Dcompile.native=true &lt;target&gt;</span>
</p>
<p>The native hadoop library is not built by default since not everyone is 
      interested in building them.</p>
<p>You should see the newly-built native hadoop library in:</p>
<p>
<span class="codefrag">$ build/native/&lt;platform&gt;/lib</span>
</p>
<p>where &lt;platform&gt; is combination of the system-properties: 
      <span class="codefrag">${os.name}-${os.arch}-${sun.arch.data.model}</span>; for e.g. 
      Linux-i386-32.</p>
<a name="N1010A"></a><a name="Notes"></a>
<h3 class="h4">Notes</h3>
<ul>
          
<li>
            It is <strong>mandatory</strong> to have both the zlib and lzo 
            development packages on the target platform for building the 
            native hadoop library; however for deployment it is sufficient to 
            install zlib or lzo if you wish to use only one of them.
          </li>
          
<li>
            It is necessary to have the correct 32/64 libraries of both zlib/lzo 
            depending on the 32/64 bit jvm for the target platform for 
            building/deployment of the native hadoop library.
          </li>
        
</ul>
</div>
    
<a name="N1011E"></a><a name="Loading+native+libraries+through+DistributedCache"></a>
<h2 class="h3"> Loading native libraries through DistributedCache </h2>
<div class="section">
<p>User can load native shared libraries through  
      <a href="mapred_tutorial.html#DistributedCache">DistributedCache</a>
      for <em>distributing</em> and <em>symlinking</em> the library files</p>
<p>Here is an example, describing how to distribute the library and
      load it from map/reduce task. </p>
<ol>
      
<li> First copy the library to the HDFS. <br>
      
<span class="codefrag">bin/hadoop fs -copyFromLocal mylib.so.1 /libraries/mylib.so.1</span>
      
</li>
      
<li> The job launching program should contain the following: <br>
      
<span class="codefrag"> DistributedCache.createSymlink(conf); </span> 
<br>
      
<span class="codefrag"> DistributedCache.addCacheFile("hdfs://host:port/libraries/mylib.so.1#mylib.so", conf);
      </span>
      
</li>
      
<li> The map/reduce task can contain: <br>
      
<span class="codefrag"> System.loadLibrary("mylib.so"); </span>
      
</li>
      
</ol>
</div>
  
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