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| 89 | <H2> |
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| 90 | <FONT SIZE="-1"> |
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| 91 | org.apache.hadoop.mapred</FONT> |
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| 92 | <BR> |
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| 93 | Interface Mapper<K1,V1,K2,V2></H2> |
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| 94 | <DL> |
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| 95 | <DT><B>All Superinterfaces:</B> <DD><A HREF="http://java.sun.com/javase/6/docs/api/java/io/Closeable.html?is-external=true" title="class or interface in java.io">Closeable</A>, <A HREF="../../../../org/apache/hadoop/mapred/JobConfigurable.html" title="interface in org.apache.hadoop.mapred">JobConfigurable</A></DD> |
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| 96 | </DL> |
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| 97 | <DL> |
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| 98 | <DT><B>All Known Subinterfaces:</B> <DD><A HREF="../../../../org/apache/hadoop/contrib/index/mapred/ILocalAnalysis.html" title="interface in org.apache.hadoop.contrib.index.mapred">ILocalAnalysis</A><K,V></DD> |
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| 99 | </DL> |
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| 100 | <DL> |
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| 101 | <DT><B>All Known Implementing Classes:</B> <DD><A HREF="../../../../org/apache/hadoop/mapred/lib/ChainMapper.html" title="class in org.apache.hadoop.mapred.lib">ChainMapper</A>, <A HREF="../../../../org/apache/hadoop/contrib/utils/join/DataJoinMapperBase.html" title="class in org.apache.hadoop.contrib.utils.join">DataJoinMapperBase</A>, <A HREF="../../../../org/apache/hadoop/contrib/utils/join/DataJoinReducerBase.html" title="class in org.apache.hadoop.contrib.utils.join">DataJoinReducerBase</A>, <A HREF="../../../../org/apache/hadoop/mapred/lib/DelegatingMapper.html" title="class in org.apache.hadoop.mapred.lib">DelegatingMapper</A>, <A HREF="../../../../org/apache/hadoop/examples/dancing/DistributedPentomino.PentMap.html" title="class in org.apache.hadoop.examples.dancing">DistributedPentomino.PentMap</A>, <A HREF="../../../../org/apache/hadoop/mapred/lib/FieldSelectionMapReduce.html" title="class in org.apache.hadoop.mapred.lib">FieldSelectionMapReduce</A>, <A HREF="../../../../org/apache/hadoop/contrib/index/example/IdentityLocalAnalysis.html" title="class in org.apache.hadoop.contrib.index.example">IdentityLocalAnalysis</A>, <A HREF="../../../../org/apache/hadoop/mapred/lib/IdentityMapper.html" title="class in org.apache.hadoop.mapred.lib">IdentityMapper</A>, <A HREF="../../../../org/apache/hadoop/contrib/index/mapred/IndexUpdateMapper.html" title="class in org.apache.hadoop.contrib.index.mapred">IndexUpdateMapper</A>, <A HREF="../../../../org/apache/hadoop/mapred/lib/InverseMapper.html" title="class in org.apache.hadoop.mapred.lib">InverseMapper</A>, <A HREF="../../../../org/apache/hadoop/contrib/utils/join/JobBase.html" title="class in org.apache.hadoop.contrib.utils.join">JobBase</A>, <A HREF="../../../../org/apache/hadoop/contrib/index/example/LineDocLocalAnalysis.html" title="class in org.apache.hadoop.contrib.index.example">LineDocLocalAnalysis</A>, <A HREF="../../../../org/apache/hadoop/examples/MultiFileWordCount.MapClass.html" title="class in org.apache.hadoop.examples">MultiFileWordCount.MapClass</A>, <A HREF="../../../../org/apache/hadoop/examples/PiEstimator.PiMapper.html" title="class in org.apache.hadoop.examples">PiEstimator.PiMapper</A>, <A HREF="../../../../org/apache/hadoop/streaming/PipeMapper.html" title="class in org.apache.hadoop.streaming">PipeMapper</A>, <A HREF="../../../../org/apache/hadoop/mapred/lib/RegexMapper.html" title="class in org.apache.hadoop.mapred.lib">RegexMapper</A>, <A HREF="../../../../org/apache/hadoop/examples/SleepJob.html" title="class in org.apache.hadoop.examples">SleepJob</A>, <A HREF="../../../../org/apache/hadoop/examples/terasort/TeraGen.SortGenMapper.html" title="class in org.apache.hadoop.examples.terasort">TeraGen.SortGenMapper</A>, <A HREF="../../../../org/apache/hadoop/mapred/lib/TokenCountMapper.html" title="class in org.apache.hadoop.mapred.lib">TokenCountMapper</A>, <A HREF="../../../../org/apache/hadoop/mapred/lib/aggregate/ValueAggregatorCombiner.html" title="class in org.apache.hadoop.mapred.lib.aggregate">ValueAggregatorCombiner</A>, <A HREF="../../../../org/apache/hadoop/mapred/lib/aggregate/ValueAggregatorJobBase.html" title="class in org.apache.hadoop.mapred.lib.aggregate">ValueAggregatorJobBase</A>, <A HREF="../../../../org/apache/hadoop/mapred/lib/aggregate/ValueAggregatorMapper.html" title="class in org.apache.hadoop.mapred.lib.aggregate">ValueAggregatorMapper</A>, <A HREF="../../../../org/apache/hadoop/mapred/lib/aggregate/ValueAggregatorReducer.html" title="class in org.apache.hadoop.mapred.lib.aggregate">ValueAggregatorReducer</A></DD> |
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| 102 | </DL> |
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| 103 | <HR> |
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| 104 | <B>Deprecated.</B> <I>Use <A HREF="../../../../org/apache/hadoop/mapreduce/Mapper.html" title="class in org.apache.hadoop.mapreduce"><CODE>Mapper</CODE></A> instead.</I> |
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| 105 | <P> |
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| 106 | <DL> |
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| 107 | <DT><PRE><FONT SIZE="-1"><A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Deprecated.html?is-external=true" title="class or interface in java.lang">@Deprecated</A> |
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| 108 | </FONT>public interface <B>Mapper<K1,V1,K2,V2></B><DT>extends <A HREF="../../../../org/apache/hadoop/mapred/JobConfigurable.html" title="interface in org.apache.hadoop.mapred">JobConfigurable</A>, <A HREF="../../../../org/apache/hadoop/io/Closeable.html" title="interface in org.apache.hadoop.io">Closeable</A></DL> |
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| 109 | </PRE> |
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| 110 | |
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| 111 | <P> |
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| 112 | Maps input key/value pairs to a set of intermediate key/value pairs. |
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| 113 | |
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| 114 | <p>Maps are the individual tasks which transform input records into a |
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| 115 | intermediate records. The transformed intermediate records need not be of |
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| 116 | the same type as the input records. A given input pair may map to zero or |
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| 117 | many output pairs.</p> |
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| 118 | |
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| 119 | <p>The Hadoop Map-Reduce framework spawns one map task for each |
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| 120 | <A HREF="../../../../org/apache/hadoop/mapred/InputSplit.html" title="interface in org.apache.hadoop.mapred"><CODE>InputSplit</CODE></A> generated by the <A HREF="../../../../org/apache/hadoop/mapred/InputFormat.html" title="interface in org.apache.hadoop.mapred"><CODE>InputFormat</CODE></A> for the job. |
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| 121 | <code>Mapper</code> implementations can access the <A HREF="../../../../org/apache/hadoop/mapred/JobConf.html" title="class in org.apache.hadoop.mapred"><CODE>JobConf</CODE></A> for the |
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| 122 | job via the <A HREF="../../../../org/apache/hadoop/mapred/JobConfigurable.html#configure(org.apache.hadoop.mapred.JobConf)"><CODE>JobConfigurable.configure(JobConf)</CODE></A> and initialize |
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| 123 | themselves. Similarly they can use the <A HREF="http://java.sun.com/javase/6/docs/api/java/io/Closeable.html?is-external=true#close()" title="class or interface in java.io"><CODE>Closeable.close()</CODE></A> method for |
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| 124 | de-initialization.</p> |
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| 125 | |
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| 126 | <p>The framework then calls |
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| 127 | <A HREF="../../../../org/apache/hadoop/mapred/Mapper.html#map(K1, V1, org.apache.hadoop.mapred.OutputCollector, org.apache.hadoop.mapred.Reporter)"><CODE>map(Object, Object, OutputCollector, Reporter)</CODE></A> |
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| 128 | for each key/value pair in the <code>InputSplit</code> for that task.</p> |
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| 129 | |
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| 130 | <p>All intermediate values associated with a given output key are |
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| 131 | subsequently grouped by the framework, and passed to a <A HREF="../../../../org/apache/hadoop/mapred/Reducer.html" title="interface in org.apache.hadoop.mapred"><CODE>Reducer</CODE></A> to |
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| 132 | determine the final output. Users can control the grouping by specifying |
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| 133 | a <code>Comparator</code> via |
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| 134 | <A HREF="../../../../org/apache/hadoop/mapred/JobConf.html#setOutputKeyComparatorClass(java.lang.Class)"><CODE>JobConf.setOutputKeyComparatorClass(Class)</CODE></A>.</p> |
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| 135 | |
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| 136 | <p>The grouped <code>Mapper</code> outputs are partitioned per |
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| 137 | <code>Reducer</code>. Users can control which keys (and hence records) go to |
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| 138 | which <code>Reducer</code> by implementing a custom <A HREF="../../../../org/apache/hadoop/mapred/Partitioner.html" title="interface in org.apache.hadoop.mapred"><CODE>Partitioner</CODE></A>. |
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| 139 | |
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| 140 | <p>Users can optionally specify a <code>combiner</code>, via |
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| 141 | <A HREF="../../../../org/apache/hadoop/mapred/JobConf.html#setCombinerClass(java.lang.Class)"><CODE>JobConf.setCombinerClass(Class)</CODE></A>, to perform local aggregation of the |
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| 142 | intermediate outputs, which helps to cut down the amount of data transferred |
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| 143 | from the <code>Mapper</code> to the <code>Reducer</code>. |
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| 144 | |
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| 145 | <p>The intermediate, grouped outputs are always stored in |
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| 146 | <A HREF="../../../../org/apache/hadoop/io/SequenceFile.html" title="class in org.apache.hadoop.io"><CODE>SequenceFile</CODE></A>s. Applications can specify if and how the intermediate |
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| 147 | outputs are to be compressed and which <A HREF="../../../../org/apache/hadoop/io/compress/CompressionCodec.html" title="interface in org.apache.hadoop.io.compress"><CODE>CompressionCodec</CODE></A>s are to be |
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| 148 | used via the <code>JobConf</code>.</p> |
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| 149 | |
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| 150 | <p>If the job has |
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| 151 | <a href="../../../../org/apache/hadoop/mapred/JobConf.html#ReducerNone">zero |
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| 152 | reduces</a> then the output of the <code>Mapper</code> is directly written |
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| 153 | to the <A HREF="../../../../org/apache/hadoop/fs/FileSystem.html" title="class in org.apache.hadoop.fs"><CODE>FileSystem</CODE></A> without grouping by keys.</p> |
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| 154 | |
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| 155 | <p>Example:</p> |
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| 156 | <p><blockquote><pre> |
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| 157 | public class MyMapper<K extends WritableComparable, V extends Writable> |
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| 158 | extends MapReduceBase implements Mapper<K, V, K, V> { |
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| 159 | |
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| 160 | static enum MyCounters { NUM_RECORDS } |
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| 161 | |
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| 162 | private String mapTaskId; |
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| 163 | private String inputFile; |
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| 164 | private int noRecords = 0; |
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| 165 | |
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| 166 | public void configure(JobConf job) { |
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| 167 | mapTaskId = job.get("mapred.task.id"); |
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| 168 | inputFile = job.get("map.input.file"); |
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| 169 | } |
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| 170 | |
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| 171 | public void map(K key, V val, |
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| 172 | OutputCollector<K, V> output, Reporter reporter) |
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| 173 | throws IOException { |
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| 174 | // Process the <key, value> pair (assume this takes a while) |
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| 175 | // ... |
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| 176 | // ... |
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| 177 | |
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| 178 | // Let the framework know that we are alive, and kicking! |
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| 179 | // reporter.progress(); |
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| 180 | |
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| 181 | // Process some more |
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| 182 | // ... |
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| 183 | // ... |
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| 184 | |
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| 185 | // Increment the no. of <key, value> pairs processed |
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| 186 | ++noRecords; |
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| 187 | |
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| 188 | // Increment counters |
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| 189 | reporter.incrCounter(NUM_RECORDS, 1); |
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| 190 | |
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| 191 | // Every 100 records update application-level status |
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| 192 | if ((noRecords%100) == 0) { |
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| 193 | reporter.setStatus(mapTaskId + " processed " + noRecords + |
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| 194 | " from input-file: " + inputFile); |
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| 195 | } |
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| 196 | |
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| 197 | // Output the result |
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| 198 | output.collect(key, val); |
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| 199 | } |
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| 200 | } |
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| 201 | </pre></blockquote></p> |
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| 202 | |
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| 203 | <p>Applications may write a custom <A HREF="../../../../org/apache/hadoop/mapred/MapRunnable.html" title="interface in org.apache.hadoop.mapred"><CODE>MapRunnable</CODE></A> to exert greater |
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| 204 | control on map processing e.g. multi-threaded <code>Mapper</code>s etc.</p> |
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| 205 | <P> |
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| 206 | |
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| 207 | <P> |
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| 208 | <DL> |
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| 209 | <DT><B>See Also:</B><DD><A HREF="../../../../org/apache/hadoop/mapred/JobConf.html" title="class in org.apache.hadoop.mapred"><CODE>JobConf</CODE></A>, |
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| 210 | <A HREF="../../../../org/apache/hadoop/mapred/InputFormat.html" title="interface in org.apache.hadoop.mapred"><CODE>InputFormat</CODE></A>, |
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| 211 | <A HREF="../../../../org/apache/hadoop/mapred/Partitioner.html" title="interface in org.apache.hadoop.mapred"><CODE>Partitioner</CODE></A>, |
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| 212 | <A HREF="../../../../org/apache/hadoop/mapred/Reducer.html" title="interface in org.apache.hadoop.mapred"><CODE>Reducer</CODE></A>, |
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| 213 | <A HREF="../../../../org/apache/hadoop/mapred/MapReduceBase.html" title="class in org.apache.hadoop.mapred"><CODE>MapReduceBase</CODE></A>, |
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| 214 | <A HREF="../../../../org/apache/hadoop/mapred/MapRunnable.html" title="interface in org.apache.hadoop.mapred"><CODE>MapRunnable</CODE></A>, |
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| 215 | <A HREF="../../../../org/apache/hadoop/io/SequenceFile.html" title="class in org.apache.hadoop.io"><CODE>SequenceFile</CODE></A></DL> |
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| 216 | <HR> |
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| 217 | |
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| 218 | <P> |
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| 219 | |
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| 220 | <!-- ========== METHOD SUMMARY =========== --> |
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| 221 | |
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| 222 | <A NAME="method_summary"><!-- --></A> |
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| 223 | <TABLE BORDER="1" WIDTH="100%" CELLPADDING="3" CELLSPACING="0" SUMMARY=""> |
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| 224 | <TR BGCOLOR="#CCCCFF" CLASS="TableHeadingColor"> |
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| 225 | <TH ALIGN="left" COLSPAN="2"><FONT SIZE="+2"> |
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| 226 | <B>Method Summary</B></FONT></TH> |
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| 227 | </TR> |
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| 228 | <TR BGCOLOR="white" CLASS="TableRowColor"> |
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| 229 | <TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1"> |
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| 230 | <CODE> void</CODE></FONT></TD> |
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| 231 | <TD><CODE><B><A HREF="../../../../org/apache/hadoop/mapred/Mapper.html#map(K1, V1, org.apache.hadoop.mapred.OutputCollector, org.apache.hadoop.mapred.Reporter)">map</A></B>(<A HREF="../../../../org/apache/hadoop/mapred/Mapper.html" title="type parameter in Mapper">K1</A> key, |
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| 232 | <A HREF="../../../../org/apache/hadoop/mapred/Mapper.html" title="type parameter in Mapper">V1</A> value, |
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| 233 | <A HREF="../../../../org/apache/hadoop/mapred/OutputCollector.html" title="interface in org.apache.hadoop.mapred">OutputCollector</A><<A HREF="../../../../org/apache/hadoop/mapred/Mapper.html" title="type parameter in Mapper">K2</A>,<A HREF="../../../../org/apache/hadoop/mapred/Mapper.html" title="type parameter in Mapper">V2</A>> output, |
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| 234 | <A HREF="../../../../org/apache/hadoop/mapred/Reporter.html" title="interface in org.apache.hadoop.mapred">Reporter</A> reporter)</CODE> |
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| 235 | |
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| 236 | <BR> |
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| 237 | <B>Deprecated.</B> Maps a single input key/value pair into an intermediate key/value pair.</TD> |
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| 238 | </TR> |
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| 239 | </TABLE> |
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| 240 | <A NAME="methods_inherited_from_class_org.apache.hadoop.mapred.JobConfigurable"><!-- --></A> |
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| 241 | <TABLE BORDER="1" WIDTH="100%" CELLPADDING="3" CELLSPACING="0" SUMMARY=""> |
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| 242 | <TR BGCOLOR="#EEEEFF" CLASS="TableSubHeadingColor"> |
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| 243 | <TH ALIGN="left"><B>Methods inherited from interface org.apache.hadoop.mapred.<A HREF="../../../../org/apache/hadoop/mapred/JobConfigurable.html" title="interface in org.apache.hadoop.mapred">JobConfigurable</A></B></TH> |
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| 244 | </TR> |
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| 245 | <TR BGCOLOR="white" CLASS="TableRowColor"> |
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| 246 | <TD><CODE><A HREF="../../../../org/apache/hadoop/mapred/JobConfigurable.html#configure(org.apache.hadoop.mapred.JobConf)">configure</A></CODE></TD> |
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| 247 | </TR> |
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| 248 | </TABLE> |
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| 249 | <A NAME="methods_inherited_from_class_java.io.Closeable"><!-- --></A> |
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| 250 | <TABLE BORDER="1" WIDTH="100%" CELLPADDING="3" CELLSPACING="0" SUMMARY=""> |
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| 251 | <TR BGCOLOR="#EEEEFF" CLASS="TableSubHeadingColor"> |
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| 252 | <TH ALIGN="left"><B>Methods inherited from interface java.io.<A HREF="http://java.sun.com/javase/6/docs/api/java/io/Closeable.html?is-external=true" title="class or interface in java.io">Closeable</A></B></TH> |
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| 253 | </TR> |
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| 254 | <TR BGCOLOR="white" CLASS="TableRowColor"> |
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| 255 | <TD><CODE><A HREF="http://java.sun.com/javase/6/docs/api/java/io/Closeable.html?is-external=true#close()" title="class or interface in java.io">close</A></CODE></TD> |
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| 256 | </TR> |
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| 257 | </TABLE> |
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| 258 | |
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| 259 | <P> |
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| 260 | |
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| 261 | <!-- ============ METHOD DETAIL ========== --> |
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| 262 | |
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| 263 | <A NAME="method_detail"><!-- --></A> |
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| 264 | <TABLE BORDER="1" WIDTH="100%" CELLPADDING="3" CELLSPACING="0" SUMMARY=""> |
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| 265 | <TR BGCOLOR="#CCCCFF" CLASS="TableHeadingColor"> |
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| 266 | <TH ALIGN="left" COLSPAN="1"><FONT SIZE="+2"> |
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| 267 | <B>Method Detail</B></FONT></TH> |
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| 268 | </TR> |
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| 269 | </TABLE> |
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| 270 | |
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| 271 | <A NAME="map(java.lang.Object,java.lang.Object,org.apache.hadoop.mapred.OutputCollector,org.apache.hadoop.mapred.Reporter)"><!-- --></A><A NAME="map(K1, V1, org.apache.hadoop.mapred.OutputCollector, org.apache.hadoop.mapred.Reporter)"><!-- --></A><H3> |
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| 272 | map</H3> |
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| 273 | <PRE> |
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| 274 | void <B>map</B>(<A HREF="../../../../org/apache/hadoop/mapred/Mapper.html" title="type parameter in Mapper">K1</A> key, |
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| 275 | <A HREF="../../../../org/apache/hadoop/mapred/Mapper.html" title="type parameter in Mapper">V1</A> value, |
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| 276 | <A HREF="../../../../org/apache/hadoop/mapred/OutputCollector.html" title="interface in org.apache.hadoop.mapred">OutputCollector</A><<A HREF="../../../../org/apache/hadoop/mapred/Mapper.html" title="type parameter in Mapper">K2</A>,<A HREF="../../../../org/apache/hadoop/mapred/Mapper.html" title="type parameter in Mapper">V2</A>> output, |
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| 277 | <A HREF="../../../../org/apache/hadoop/mapred/Reporter.html" title="interface in org.apache.hadoop.mapred">Reporter</A> reporter) |
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| 278 | throws <A HREF="http://java.sun.com/javase/6/docs/api/java/io/IOException.html?is-external=true" title="class or interface in java.io">IOException</A></PRE> |
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| 279 | <DL> |
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| 280 | <DD><B>Deprecated.</B> <DD>Maps a single input key/value pair into an intermediate key/value pair. |
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| 281 | |
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| 282 | <p>Output pairs need not be of the same types as input pairs. A given |
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| 283 | input pair may map to zero or many output pairs. Output pairs are |
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| 284 | collected with calls to |
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| 285 | <A HREF="../../../../org/apache/hadoop/mapred/OutputCollector.html#collect(K, V)"><CODE>OutputCollector.collect(Object,Object)</CODE></A>.</p> |
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| 286 | |
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| 287 | <p>Applications can use the <A HREF="../../../../org/apache/hadoop/mapred/Reporter.html" title="interface in org.apache.hadoop.mapred"><CODE>Reporter</CODE></A> provided to report progress |
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| 288 | or just indicate that they are alive. In scenarios where the application |
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| 289 | takes an insignificant amount of time to process individual key/value |
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| 290 | pairs, this is crucial since the framework might assume that the task has |
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| 291 | timed-out and kill that task. The other way of avoiding this is to set |
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| 292 | <a href="../../../../../mapred-default.html#mapred.task.timeout"> |
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| 293 | mapred.task.timeout</a> to a high-enough value (or even zero for no |
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| 294 | time-outs).</p> |
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| 295 | <P> |
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| 296 | <DD><DL> |
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| 297 | </DL> |
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| 298 | </DD> |
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| 299 | <DD><DL> |
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| 300 | <DT><B>Parameters:</B><DD><CODE>key</CODE> - the input key.<DD><CODE>value</CODE> - the input value.<DD><CODE>output</CODE> - collects mapped keys and values.<DD><CODE>reporter</CODE> - facility to report progress. |
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| 301 | <DT><B>Throws:</B> |
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| 302 | <DD><CODE><A HREF="http://java.sun.com/javase/6/docs/api/java/io/IOException.html?is-external=true" title="class or interface in java.io">IOException</A></CODE></DL> |
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