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           <h1>Using in MapReduce</h1>
           <p>This page describes how to read and write ORC files from Hadoop’s
 newer org.apache.hadoop.mapreduce MapReduce APIs. If you want to use the
 older org.apache.hadoop.mapred API, please look at the <a href="/docs/mapred.html">previous
 page</a>.</p>

 <h2 id="reading-orc-files">Reading ORC files</h2>

 <p>Add ORC and your desired version of Hadoop to your <code class="highlighter-rouge">pom.xml</code>:</p>

 <div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt">&lt;dependencies&gt;</span>
   <span class="nt">&lt;dependency&gt;</span>
     <span class="nt">&lt;groupId&gt;</span>org.apache.orc<span class="nt">&lt;/groupId&gt;</span>
     <span class="nt">&lt;artifactId&gt;</span>orc-mapreduce<span class="nt">&lt;/artifactId&gt;</span>
     <span class="nt">&lt;version&gt;</span>1.1.0<span class="nt">&lt;/version&gt;</span>
   <span class="nt">&lt;/dependency&gt;</span>
   <span class="nt">&lt;dependency&gt;</span>
     <span class="nt">&lt;groupId&gt;</span>org.apache.hadoop<span class="nt">&lt;/groupId&gt;</span>
     <span class="nt">&lt;artifactId&gt;</span>hadoop-mapreduce-client-core<span class="nt">&lt;/artifactId&gt;</span>
     <span class="nt">&lt;version&gt;</span>2.7.0<span class="nt">&lt;/version&gt;</span>
   <span class="nt">&lt;/dependency&gt;</span>
 <span class="nt">&lt;/dependencies&gt;</span>
 </code></pre></div></div>

 <p>Set the minimal properties in your JobConf:</p>

 <ul>
   <li><strong>mapreduce.job.inputformat.class</strong> = <a href="/api/orc-mapreduce/index.html?org/apache/orc/mapreduce/OrcInputFormat.html">org.apache.orc.mapreduce.OrcInputFormat</a></li>
   <li><strong>mapreduce.input.fileinputformat.inputdir</strong> = your input directory</li>
 </ul>

 <p>ORC files contain a series of values of the same type and that type
 schema is encoded in the file. Because the ORC files are
 self-describing, the reader always knows how to correctly interpret
 the data. All of the ORC files written by Hive and most of the others have
 a struct as the value type.</p>

 <p>Your Mapper class will receive org.apache.hadoop.io.NullWritable as
 the key and a value based on the table below expanded recursively.</p>

 <table>
   <thead>
     <tr>
       <th>ORC Type</th>
       <th>Writable Type</th>
     </tr>
   </thead>
   <tbody>
     <tr>
       <td>array</td>
       <td><a href="/api/orc-mapreduce/index.html?org/apache/orc/mapred/OrcStruct.html">org.apache.orc.mapred.OrcList</a></td>
     </tr>
     <tr>
       <td>binary</td>
       <td>org.apache.hadoop.io.BytesWritable</td>
     </tr>
     <tr>
       <td>bigint</td>
       <td>org.apache.hadoop.io.LongWritable</td>
     </tr>
     <tr>
       <td>boolean</td>
       <td>org.apache.hadoop.io.BooleanWritable</td>
     </tr>
     <tr>
       <td>char</td>
       <td>org.apache.hadoop.io.Text</td>
     </tr>
     <tr>
       <td>date</td>
       <td><a href="https://javadoc.io/static/org.apache.hive/hive-storage-api/2.8.1/org/apache/hadoop/hive/serde2/io/DateWritable.html">org.apache.hadoop.hive.serde2.io.DateWritable</a></td>
     </tr>
     <tr>
       <td>decimal</td>
       <td><a href="https://javadoc.io/static/org.apache.hive/hive-storage-api/2.8.1/org/apache/hadoop/hive/serde2/io/HiveDecimalWritable.html">org.apache.hadoop.hive.serde2.io.HiveDecimalWritable</a></td>
     </tr>
     <tr>
       <td>double</td>
       <td>org.apache.hadoop.io.DoubleWritable</td>
     </tr>
     <tr>
       <td>float</td>
       <td>org.apache.hadoop.io.FloatWritable</td>
     </tr>
     <tr>
       <td>int</td>
       <td>org.apache.hadoop.io.IntWritable</td>
     </tr>
     <tr>
       <td>map</td>
       <td><a href="/api/orc-mapreduce/index.html?org/apache/orc/mapred/OrcMap.html">org.apache.orc.mapred.OrcMap</a></td>
     </tr>
     <tr>
       <td>smallint</td>
       <td>org.apache.hadoop.io.ShortWritable</td>
     </tr>
     <tr>
       <td>string</td>
       <td>org.apache.hadoop.io.Text</td>
     </tr>
     <tr>
       <td>struct</td>
       <td><a href="/api/orc-mapreduce/index.html?org/apache/orc/mapred/OrcStruct.html">org.apache.orc.mapred.OrcStruct</a></td>
     </tr>
     <tr>
       <td>timestamp</td>
       <td><a href="/api/orc-mapreduce/index.html?org/apache/orc/mapred/OrcTimestamp.html">org.apache.orc.mapred.OrcTimestamp</a></td>
     </tr>
     <tr>
       <td>tinyint</td>
       <td>org.apache.hadoop.io.ByteWritable</td>
     </tr>
     <tr>
       <td>uniontype</td>
       <td><a href="/api/orc-mapreduce/index.html?org/apache/orc/mapred/OrcUnion.html">org.apache.orc.mapred.OrcUnion</a></td>
     </tr>
     <tr>
       <td>varchar</td>
       <td>org.apache.hadoop.io.Text</td>
     </tr>
   </tbody>
 </table>

 <p>Let’s assume that your input directory contains ORC files with the
 schema <code class="highlighter-rouge">struct&lt;s:string,i:int&gt;</code> and you want to use the string field
 as the key to the MapReduce shuffle and the integer as the value. The
 mapper code would look like:</p>

 <div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kd">public</span> <span class="kd">static</span> <span class="kd">class</span> <span class="nc">MyMapper</span>
     <span class="kd">extends</span> <span class="nc">Mapper</span><span class="o">&lt;</span><span class="nc">NullWritable</span><span class="o">,</span><span class="nc">OrcStruct</span><span class="o">,</span><span class="nc">Text</span><span class="o">,</span><span class="nc">IntWritable</span><span class="o">&gt;</span> <span class="o">{</span>

   <span class="c1">// Assume the ORC file has type: struct&lt;s:string,i:int&gt;</span>
   <span class="kd">public</span> <span class="kt">void</span> <span class="nf">map</span><span class="o">(</span><span class="nc">NullWritable</span> <span class="n">key</span><span class="o">,</span> <span class="nc">OrcStruct</span> <span class="n">value</span><span class="o">,</span>
                   <span class="nc">Context</span> <span class="n">output</span><span class="o">)</span> <span class="kd">throws</span> <span class="nc">IOException</span><span class="o">,</span> <span class="nc">InterruptedException</span> <span class="o">{</span>
     <span class="c1">// take the first field as the key and the second field as the value</span>
     <span class="n">output</span><span class="o">.</span><span class="na">write</span><span class="o">((</span><span class="nc">Text</span><span class="o">)</span> <span class="n">value</span><span class="o">.</span><span class="na">getFieldValue</span><span class="o">(</span><span class="mi">0</span><span class="o">),</span>
                  <span class="o">(</span><span class="nc">IntWritable</span><span class="o">)</span> <span class="n">value</span><span class="o">.</span><span class="na">getFieldValue</span><span class="o">(</span><span class="mi">1</span><span class="o">));</span>
   <span class="o">}</span>
 <span class="o">}</span>
 </code></pre></div></div>

 <h2 id="writing-orc-files">Writing ORC files</h2>

 <p>To write ORC files from your MapReduce job, you’ll need to set</p>

 <ul>
   <li><strong>mapreduce.job.outputformat.class</strong> = <a href="/api/orc-mapreduce/index.html?org/apache/orc/mapreduce/OrcOutputFormat.html">org.apache.orc.mapreduce.OrcOutputFormat</a></li>
   <li><strong>mapreduce.output.fileoutputformat.outputdir</strong> = your output directory</li>
   <li><strong>orc.mapred.output.schema</strong> = the schema to write to the ORC file</li>
 </ul>

 <p>The reducer needs to create the Writable value to be put into the ORC
 file and typically uses the OrcStruct.createValue(TypeDescription)
 function. For our example, let’s assume that the shuffle types are
 (Text, IntWritable) from the previous section and the reduce should
 gather the integer for each key together and write them as a list. The
 output schema would be <code class="highlighter-rouge">struct&lt;key:string,ints:array&lt;int&gt;&gt;</code>. As always
 with MapReduce, if your method stores the values, you need to copy their
 value before getting the next.</p>

 <div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kd">public</span> <span class="kd">static</span> <span class="kd">class</span> <span class="nc">MyReducer</span>
   <span class="kd">extends</span> <span class="nc">Reducer</span><span class="o">&lt;</span><span class="nc">Text</span><span class="o">,</span><span class="nc">IntWritable</span><span class="o">,</span><span class="nc">NullWritable</span><span class="o">,</span><span class="nc">OrcStruct</span><span class="o">&gt;</span> <span class="o">{</span>

   <span class="kd">private</span> <span class="nc">TypeDescription</span> <span class="n">schema</span> <span class="o">=</span>
     <span class="nc">TypeDescription</span><span class="o">.</span><span class="na">fromString</span><span class="o">(</span><span class="s">"struct&lt;key:string,ints:array&lt;int&gt;&gt;"</span><span class="o">);</span>
   <span class="c1">// createValue creates the correct value type for the schema</span>
   <span class="kd">private</span> <span class="nc">OrcStruct</span> <span class="n">pair</span> <span class="o">=</span> <span class="o">(</span><span class="nc">OrcStruct</span><span class="o">)</span> <span class="nc">OrcStruct</span><span class="o">.</span><span class="na">createValue</span><span class="o">(</span><span class="n">schema</span><span class="o">);</span>
   <span class="c1">// get a handle to the list of ints</span>
   <span class="kd">private</span> <span class="nc">OrcList</span><span class="o">&lt;</span><span class="nc">IntWritable</span><span class="o">&gt;</span> <span class="n">valueList</span> <span class="o">=</span>
     <span class="o">(</span><span class="nc">OrcList</span><span class="o">&lt;</span><span class="nc">IntWritable</span><span class="o">&gt;)</span> <span class="n">pair</span><span class="o">.</span><span class="na">getFieldValue</span><span class="o">(</span><span class="mi">1</span><span class="o">);</span>
   <span class="kd">private</span> <span class="kd">final</span> <span class="nc">NullWritable</span> <span class="n">nada</span> <span class="o">=</span> <span class="nc">NullWritable</span><span class="o">.</span><span class="na">get</span><span class="o">();</span>

   <span class="kd">public</span> <span class="kt">void</span> <span class="nf">reduce</span><span class="o">(</span><span class="nc">Text</span> <span class="n">key</span><span class="o">,</span> <span class="nc">Iterable</span><span class="o">&lt;</span><span class="nc">IntWritable</span><span class="o">&gt;</span> <span class="n">values</span><span class="o">,</span>
                      <span class="nc">Context</span> <span class="n">output</span>
                      <span class="o">)</span> <span class="kd">throws</span> <span class="nc">IOException</span><span class="o">,</span> <span class="nc">InterruptedException</span> <span class="o">{</span>
     <span class="n">pair</span><span class="o">.</span><span class="na">setFieldValue</span><span class="o">(</span><span class="mi">0</span><span class="o">,</span> <span class="n">key</span><span class="o">);</span>
     <span class="n">valueList</span><span class="o">.</span><span class="na">clear</span><span class="o">();</span>
     <span class="k">for</span><span class="o">(</span><span class="nc">IntWritable</span> <span class="nl">val:</span> <span class="n">values</span><span class="o">)</span> <span class="o">{</span>
       <span class="n">valueList</span><span class="o">.</span><span class="na">add</span><span class="o">(</span><span class="k">new</span> <span class="nc">IntWritable</span><span class="o">(</span><span class="n">val</span><span class="o">.</span><span class="na">get</span><span class="o">()));</span>
     <span class="o">}</span>
     <span class="n">output</span><span class="o">.</span><span class="na">write</span><span class="o">(</span><span class="n">nada</span><span class="o">,</span> <span class="n">pair</span><span class="o">);</span>
   <span class="o">}</span>
 <span class="o">}</span>
 </code></pre></div></div>

 <h2 id="sending-orcstruct-orclist-orcmap-or-orcunion-through-the-shuffle">Sending OrcStruct, OrcList, OrcMap, or OrcUnion through the Shuffle</h2>

 <p>In the previous examples, only the Hadoop types were sent through the
 MapReduce shuffle. The complex ORC types, since they are generic
 types, need to have their full type information provided to create the
 object. To enable MapReduce to properly instantiate the OrcStruct and
 other ORC types, we need to wrap it in either an
 <a href="/api/orc-mapreduce/index.html?org/apache/orc/mapred/OrcKey.html">OrcKey</a>
 for the shuffle key or
 <a href="/api/orc-mapreduce/index.html?org/apache/orc/mapred/OrcValue.html">OrcValue</a>
 for the shuffle value.</p>

 <p>To send two OrcStructs through the shuffle, define the following properties
 in the JobConf:</p>

 <ul>
   <li><strong>mapreduce.map.output.key.class</strong> = org.apache.orc.mapred.OrcKey</li>
   <li><strong>orc.mapred.map.output.key.schema</strong> = the shuffle key’s schema</li>
   <li><strong>mapreduce.map.output.value.class</strong> = org.apache.orc.mapred.OrcValue</li>
   <li><strong>orc.mapred.map.output.value.schema</strong> = the shuffle value’s schema</li>
 </ul>

 <p>The mapper just adds an OrcKey and OrcWrapper around the key and value
 respectively. These objects should be created once and reused as the mapper
 runs.</p>

 <div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kd">public</span> <span class="kd">static</span> <span class="kd">class</span> <span class="nc">MyMapperShuffle</span>
     <span class="kd">extends</span> <span class="nc">Mapper</span><span class="o">&lt;</span><span class="nc">NullWritable</span><span class="o">,</span><span class="nc">OrcStruct</span><span class="o">,</span><span class="nc">OrcKey</span><span class="o">,</span><span class="nc">OrcValue</span><span class="o">&gt;</span> <span class="o">{</span>
   <span class="kd">private</span> <span class="nc">OrcKey</span> <span class="n">keyWrapper</span> <span class="o">=</span> <span class="k">new</span> <span class="nc">OrcKey</span><span class="o">();</span>
   <span class="kd">private</span> <span class="nc">OrcValue</span> <span class="n">valueWrapper</span> <span class="o">=</span> <span class="k">new</span> <span class="nc">OrcValue</span><span class="o">();</span>
   <span class="kd">private</span> <span class="nc">OrcStruct</span> <span class="n">outStruct</span> <span class="o">=</span> <span class="o">(</span><span class="nc">OrcStruct</span><span class="o">)</span> <span class="nc">OrcStruct</span><span class="o">.</span><span class="na">createValue</span>
     <span class="o">(</span><span class="nc">TypeDescription</span><span class="o">.</span><span class="na">fromString</span><span class="o">(</span><span class="s">"struct&lt;i:int,j:int&gt;"</span><span class="o">));</span>
   <span class="kd">private</span> <span class="nc">IntWritable</span> <span class="n">i</span> <span class="o">=</span> <span class="o">(</span><span class="nc">IntWritable</span><span class="o">)</span> <span class="n">outStruct</span><span class="o">.</span><span class="na">getFieldValue</span><span class="o">(</span><span class="s">"i"</span><span class="o">);</span>
   <span class="kd">private</span> <span class="nc">IntWritable</span> <span class="n">j</span> <span class="o">=</span> <span class="o">(</span><span class="nc">IntWritable</span><span class="o">)</span> <span class="n">outStruct</span><span class="o">.</span><span class="na">getFieldValue</span><span class="o">(</span><span class="s">"j"</span><span class="o">);</span>

   <span class="c1">// Assume the input has type: struct&lt;s:string,i:int&gt;</span>
   <span class="kd">public</span> <span class="kt">void</span> <span class="nf">map</span><span class="o">(</span><span class="nc">NullWritable</span> <span class="n">key</span><span class="o">,</span> <span class="nc">OrcStruct</span> <span class="n">value</span><span class="o">,</span>
                   <span class="nc">Context</span> <span class="n">output</span><span class="o">)</span> <span class="kd">throws</span> <span class="nc">IOException</span><span class="o">,</span> <span class="nc">InterruptedException</span> <span class="o">{</span>
     <span class="n">keyWrapper</span><span class="o">.</span><span class="na">key</span> <span class="o">=</span> <span class="n">value</span><span class="o">;</span>
     <span class="n">valueWrapper</span><span class="o">.</span><span class="na">value</span> <span class="o">=</span> <span class="n">outStruct</span><span class="o">;</span>
     <span class="kt">int</span> <span class="n">val</span> <span class="o">=</span> <span class="o">((</span><span class="nc">IntWritable</span><span class="o">)</span> <span class="n">value</span><span class="o">.</span><span class="na">getFieldValue</span><span class="o">(</span><span class="s">"i"</span><span class="o">)).</span><span class="na">get</span><span class="o">();</span>
     <span class="n">i</span><span class="o">.</span><span class="na">set</span><span class="o">(</span><span class="n">val</span> <span class="o">*</span> <span class="mi">2</span><span class="o">);</span>
     <span class="n">j</span><span class="o">.</span><span class="na">set</span><span class="o">(</span><span class="n">val</span> <span class="o">*</span> <span class="n">val</span><span class="o">);</span>
     <span class="n">output</span><span class="o">.</span><span class="na">write</span><span class="o">(</span><span class="n">keyWrapper</span><span class="o">,</span> <span class="n">valueWrapper</span><span class="o">);</span>
   <span class="o">}</span>
 <span class="o">}</span>
 </code></pre></div></div>

 <p>The reducer code accesses the underlying OrcStructs by using the
 OrcKey.key and OrcValue.value fields.</p>


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