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7org.apache.hadoop.mapred (Hadoop 0.20.1 API)
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82<H2>
83Package org.apache.hadoop.mapred
84</H2>
85A software framework for easily writing applications which process vast
86amounts of data (multi-terabyte data-sets) parallelly on large clusters
87(thousands of nodes) built of commodity hardware in a reliable, fault-tolerant
88manner.
89<P>
90<B>See:</B>
91<BR>
92&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<A HREF="#package_description"><B>Description</B></A>
93<P>
94
95<TABLE BORDER="1" WIDTH="100%" CELLPADDING="3" CELLSPACING="0" SUMMARY="">
96<TR BGCOLOR="#CCCCFF" CLASS="TableHeadingColor">
97<TH ALIGN="left" COLSPAN="2"><FONT SIZE="+2">
98<B>Interface Summary</B></FONT></TH>
99</TR>
100<TR BGCOLOR="white" CLASS="TableRowColor">
101<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/InputFormat.html" title="interface in org.apache.hadoop.mapred">InputFormat&lt;K,V&gt;</A></B></TD>
102<TD><B>Deprecated.</B>&nbsp;<I>Use <A HREF="../../../../org/apache/hadoop/mapreduce/InputFormat.html" title="class in org.apache.hadoop.mapreduce"><CODE>InputFormat</CODE></A> instead.</I></TD>
103</TR>
104<TR BGCOLOR="white" CLASS="TableRowColor">
105<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/InputSplit.html" title="interface in org.apache.hadoop.mapred">InputSplit</A></B></TD>
106<TD><B>Deprecated.</B>&nbsp;<I>Use <A HREF="../../../../org/apache/hadoop/mapreduce/InputSplit.html" title="class in org.apache.hadoop.mapreduce"><CODE>InputSplit</CODE></A> instead.</I></TD>
107</TR>
108<TR BGCOLOR="white" CLASS="TableRowColor">
109<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/JobConfigurable.html" title="interface in org.apache.hadoop.mapred">JobConfigurable</A></B></TD>
110<TD><B>Deprecated.</B></TD>
111</TR>
112<TR BGCOLOR="white" CLASS="TableRowColor">
113<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/JobHistory.Listener.html" title="interface in org.apache.hadoop.mapred">JobHistory.Listener</A></B></TD>
114<TD>Callback interface for reading back log events from JobHistory.</TD>
115</TR>
116<TR BGCOLOR="white" CLASS="TableRowColor">
117<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/Mapper.html" title="interface in org.apache.hadoop.mapred">Mapper&lt;K1,V1,K2,V2&gt;</A></B></TD>
118<TD><B>Deprecated.</B>&nbsp;<I>Use <A HREF="../../../../org/apache/hadoop/mapreduce/Mapper.html" title="class in org.apache.hadoop.mapreduce"><CODE>Mapper</CODE></A> instead.</I></TD>
119</TR>
120<TR BGCOLOR="white" CLASS="TableRowColor">
121<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/MapRunnable.html" title="interface in org.apache.hadoop.mapred">MapRunnable&lt;K1,V1,K2,V2&gt;</A></B></TD>
122<TD><B>Deprecated.</B>&nbsp;<I>Use <A HREF="../../../../org/apache/hadoop/mapreduce/Mapper.html" title="class in org.apache.hadoop.mapreduce"><CODE>Mapper</CODE></A> instead.</I></TD>
123</TR>
124<TR BGCOLOR="white" CLASS="TableRowColor">
125<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/OutputCollector.html" title="interface in org.apache.hadoop.mapred">OutputCollector&lt;K,V&gt;</A></B></TD>
126<TD>Collects the <code>&lt;key, value&gt;</code> pairs output by <A HREF="../../../../org/apache/hadoop/mapred/Mapper.html" title="interface in org.apache.hadoop.mapred"><CODE>Mapper</CODE></A>s
127 and <A HREF="../../../../org/apache/hadoop/mapred/Reducer.html" title="interface in org.apache.hadoop.mapred"><CODE>Reducer</CODE></A>s.</TD>
128</TR>
129<TR BGCOLOR="white" CLASS="TableRowColor">
130<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/OutputFormat.html" title="interface in org.apache.hadoop.mapred">OutputFormat&lt;K,V&gt;</A></B></TD>
131<TD><B>Deprecated.</B>&nbsp;<I>Use <A HREF="../../../../org/apache/hadoop/mapreduce/OutputFormat.html" title="class in org.apache.hadoop.mapreduce"><CODE>OutputFormat</CODE></A> instead.</I></TD>
132</TR>
133<TR BGCOLOR="white" CLASS="TableRowColor">
134<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/Partitioner.html" title="interface in org.apache.hadoop.mapred">Partitioner&lt;K2,V2&gt;</A></B></TD>
135<TD><B>Deprecated.</B>&nbsp;<I>Use <A HREF="../../../../org/apache/hadoop/mapreduce/Partitioner.html" title="class in org.apache.hadoop.mapreduce"><CODE>Partitioner</CODE></A> instead.</I></TD>
136</TR>
137<TR BGCOLOR="white" CLASS="TableRowColor">
138<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/RawKeyValueIterator.html" title="interface in org.apache.hadoop.mapred">RawKeyValueIterator</A></B></TD>
139<TD><code>RawKeyValueIterator</code> is an iterator used to iterate over
140 the raw keys and values during sort/merge of intermediate data.</TD>
141</TR>
142<TR BGCOLOR="white" CLASS="TableRowColor">
143<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/RecordReader.html" title="interface in org.apache.hadoop.mapred">RecordReader&lt;K,V&gt;</A></B></TD>
144<TD><code>RecordReader</code> reads &lt;key, value&gt; pairs from an
145 <A HREF="../../../../org/apache/hadoop/mapred/InputSplit.html" title="interface in org.apache.hadoop.mapred"><CODE>InputSplit</CODE></A>.</TD>
146</TR>
147<TR BGCOLOR="white" CLASS="TableRowColor">
148<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/RecordWriter.html" title="interface in org.apache.hadoop.mapred">RecordWriter&lt;K,V&gt;</A></B></TD>
149<TD><code>RecordWriter</code> writes the output &lt;key, value&gt; pairs
150 to an output file.</TD>
151</TR>
152<TR BGCOLOR="white" CLASS="TableRowColor">
153<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/Reducer.html" title="interface in org.apache.hadoop.mapred">Reducer&lt;K2,V2,K3,V3&gt;</A></B></TD>
154<TD><B>Deprecated.</B>&nbsp;<I>Use <A HREF="../../../../org/apache/hadoop/mapreduce/Reducer.html" title="class in org.apache.hadoop.mapreduce"><CODE>Reducer</CODE></A> instead.</I></TD>
155</TR>
156<TR BGCOLOR="white" CLASS="TableRowColor">
157<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/Reporter.html" title="interface in org.apache.hadoop.mapred">Reporter</A></B></TD>
158<TD>A facility for Map-Reduce applications to report progress and update
159 counters, status information etc.</TD>
160</TR>
161<TR BGCOLOR="white" CLASS="TableRowColor">
162<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/RunningJob.html" title="interface in org.apache.hadoop.mapred">RunningJob</A></B></TD>
163<TD><code>RunningJob</code> is the user-interface to query for details on a
164 running Map-Reduce job.</TD>
165</TR>
166<TR BGCOLOR="white" CLASS="TableRowColor">
167<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/SequenceFileInputFilter.Filter.html" title="interface in org.apache.hadoop.mapred">SequenceFileInputFilter.Filter</A></B></TD>
168<TD>filter interface</TD>
169</TR>
170</TABLE>
171&nbsp;
172
173<P>
174
175<TABLE BORDER="1" WIDTH="100%" CELLPADDING="3" CELLSPACING="0" SUMMARY="">
176<TR BGCOLOR="#CCCCFF" CLASS="TableHeadingColor">
177<TH ALIGN="left" COLSPAN="2"><FONT SIZE="+2">
178<B>Class Summary</B></FONT></TH>
179</TR>
180<TR BGCOLOR="white" CLASS="TableRowColor">
181<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/ClusterStatus.html" title="class in org.apache.hadoop.mapred">ClusterStatus</A></B></TD>
182<TD>Status information on the current state of the Map-Reduce cluster.</TD>
183</TR>
184<TR BGCOLOR="white" CLASS="TableRowColor">
185<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/Counters.html" title="class in org.apache.hadoop.mapred">Counters</A></B></TD>
186<TD><B>Deprecated.</B>&nbsp;<I>Use <A HREF="../../../../org/apache/hadoop/mapreduce/Counters.html" title="class in org.apache.hadoop.mapreduce"><CODE>Counters</CODE></A> instead.</I></TD>
187</TR>
188<TR BGCOLOR="white" CLASS="TableRowColor">
189<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/Counters.Counter.html" title="class in org.apache.hadoop.mapred">Counters.Counter</A></B></TD>
190<TD>A counter record, comprising its name and value.</TD>
191</TR>
192<TR BGCOLOR="white" CLASS="TableRowColor">
193<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/Counters.Group.html" title="class in org.apache.hadoop.mapred">Counters.Group</A></B></TD>
194<TD><code>Group</code> of counters, comprising of counters from a particular
195  counter <A HREF="http://java.sun.com/javase/6/docs/api/java/lang/Enum.html?is-external=true" title="class or interface in java.lang"><CODE>Enum</CODE></A> class.</TD>
196</TR>
197<TR BGCOLOR="white" CLASS="TableRowColor">
198<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/DefaultJobHistoryParser.html" title="class in org.apache.hadoop.mapred">DefaultJobHistoryParser</A></B></TD>
199<TD>Default parser for job history files.</TD>
200</TR>
201<TR BGCOLOR="white" CLASS="TableRowColor">
202<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/FileInputFormat.html" title="class in org.apache.hadoop.mapred">FileInputFormat&lt;K,V&gt;</A></B></TD>
203<TD><B>Deprecated.</B>&nbsp;<I>Use <A HREF="../../../../org/apache/hadoop/mapreduce/lib/input/FileInputFormat.html" title="class in org.apache.hadoop.mapreduce.lib.input"><CODE>FileInputFormat</CODE></A>
204  instead.</I></TD>
205</TR>
206<TR BGCOLOR="white" CLASS="TableRowColor">
207<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/FileOutputCommitter.html" title="class in org.apache.hadoop.mapred">FileOutputCommitter</A></B></TD>
208<TD>An <A HREF="../../../../org/apache/hadoop/mapred/OutputCommitter.html" title="class in org.apache.hadoop.mapred"><CODE>OutputCommitter</CODE></A> that commits files specified
209 in job output directory i.e.</TD>
210</TR>
211<TR BGCOLOR="white" CLASS="TableRowColor">
212<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/FileOutputFormat.html" title="class in org.apache.hadoop.mapred">FileOutputFormat&lt;K,V&gt;</A></B></TD>
213<TD>A base class for <A HREF="../../../../org/apache/hadoop/mapred/OutputFormat.html" title="interface in org.apache.hadoop.mapred"><CODE>OutputFormat</CODE></A>.</TD>
214</TR>
215<TR BGCOLOR="white" CLASS="TableRowColor">
216<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/FileSplit.html" title="class in org.apache.hadoop.mapred">FileSplit</A></B></TD>
217<TD><B>Deprecated.</B>&nbsp;<I>Use <A HREF="../../../../org/apache/hadoop/mapreduce/lib/input/FileSplit.html" title="class in org.apache.hadoop.mapreduce.lib.input"><CODE>FileSplit</CODE></A>
218  instead.</I></TD>
219</TR>
220<TR BGCOLOR="white" CLASS="TableRowColor">
221<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/ID.html" title="class in org.apache.hadoop.mapred">ID</A></B></TD>
222<TD><B>Deprecated.</B></TD>
223</TR>
224<TR BGCOLOR="white" CLASS="TableRowColor">
225<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/IsolationRunner.html" title="class in org.apache.hadoop.mapred">IsolationRunner</A></B></TD>
226<TD>&nbsp;</TD>
227</TR>
228<TR BGCOLOR="white" CLASS="TableRowColor">
229<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/JobClient.html" title="class in org.apache.hadoop.mapred">JobClient</A></B></TD>
230<TD><code>JobClient</code> is the primary interface for the user-job to interact
231 with the <A HREF="../../../../org/apache/hadoop/mapred/JobTracker.html" title="class in org.apache.hadoop.mapred"><CODE>JobTracker</CODE></A>.</TD>
232</TR>
233<TR BGCOLOR="white" CLASS="TableRowColor">
234<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/JobConf.html" title="class in org.apache.hadoop.mapred">JobConf</A></B></TD>
235<TD><B>Deprecated.</B>&nbsp;<I>Use <A HREF="../../../../org/apache/hadoop/conf/Configuration.html" title="class in org.apache.hadoop.conf"><CODE>Configuration</CODE></A> instead</I></TD>
236</TR>
237<TR BGCOLOR="white" CLASS="TableRowColor">
238<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/JobContext.html" title="class in org.apache.hadoop.mapred">JobContext</A></B></TD>
239<TD><B>Deprecated.</B>&nbsp;<I>Use <A HREF="../../../../org/apache/hadoop/mapreduce/JobContext.html" title="class in org.apache.hadoop.mapreduce"><CODE>JobContext</CODE></A> instead.</I></TD>
240</TR>
241<TR BGCOLOR="white" CLASS="TableRowColor">
242<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/JobEndNotifier.html" title="class in org.apache.hadoop.mapred">JobEndNotifier</A></B></TD>
243<TD>&nbsp;</TD>
244</TR>
245<TR BGCOLOR="white" CLASS="TableRowColor">
246<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/JobHistory.html" title="class in org.apache.hadoop.mapred">JobHistory</A></B></TD>
247<TD>Provides methods for writing to and reading from job history.</TD>
248</TR>
249<TR BGCOLOR="white" CLASS="TableRowColor">
250<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/JobHistory.HistoryCleaner.html" title="class in org.apache.hadoop.mapred">JobHistory.HistoryCleaner</A></B></TD>
251<TD>Delete history files older than one month.</TD>
252</TR>
253<TR BGCOLOR="white" CLASS="TableRowColor">
254<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/JobHistory.JobInfo.html" title="class in org.apache.hadoop.mapred">JobHistory.JobInfo</A></B></TD>
255<TD>Helper class for logging or reading back events related to job start, finish or failure.</TD>
256</TR>
257<TR BGCOLOR="white" CLASS="TableRowColor">
258<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/JobHistory.MapAttempt.html" title="class in org.apache.hadoop.mapred">JobHistory.MapAttempt</A></B></TD>
259<TD>Helper class for logging or reading back events related to start, finish or failure of
260 a Map Attempt on a node.</TD>
261</TR>
262<TR BGCOLOR="white" CLASS="TableRowColor">
263<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/JobHistory.ReduceAttempt.html" title="class in org.apache.hadoop.mapred">JobHistory.ReduceAttempt</A></B></TD>
264<TD>Helper class for logging or reading back events related to start, finish or failure of
265 a Map Attempt on a node.</TD>
266</TR>
267<TR BGCOLOR="white" CLASS="TableRowColor">
268<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/JobHistory.Task.html" title="class in org.apache.hadoop.mapred">JobHistory.Task</A></B></TD>
269<TD>Helper class for logging or reading back events related to Task's start, finish or failure.</TD>
270</TR>
271<TR BGCOLOR="white" CLASS="TableRowColor">
272<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/JobHistory.TaskAttempt.html" title="class in org.apache.hadoop.mapred">JobHistory.TaskAttempt</A></B></TD>
273<TD>Base class for Map and Reduce TaskAttempts.</TD>
274</TR>
275<TR BGCOLOR="white" CLASS="TableRowColor">
276<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/JobID.html" title="class in org.apache.hadoop.mapred">JobID</A></B></TD>
277<TD><B>Deprecated.</B></TD>
278</TR>
279<TR BGCOLOR="white" CLASS="TableRowColor">
280<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/JobProfile.html" title="class in org.apache.hadoop.mapred">JobProfile</A></B></TD>
281<TD>A JobProfile is a MapReduce primitive.</TD>
282</TR>
283<TR BGCOLOR="white" CLASS="TableRowColor">
284<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/JobQueueInfo.html" title="class in org.apache.hadoop.mapred">JobQueueInfo</A></B></TD>
285<TD>Class that contains the information regarding the Job Queues which are
286 maintained by the Hadoop Map/Reduce framework.</TD>
287</TR>
288<TR BGCOLOR="white" CLASS="TableRowColor">
289<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/JobStatus.html" title="class in org.apache.hadoop.mapred">JobStatus</A></B></TD>
290<TD>Describes the current status of a job.</TD>
291</TR>
292<TR BGCOLOR="white" CLASS="TableRowColor">
293<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/JobTracker.html" title="class in org.apache.hadoop.mapred">JobTracker</A></B></TD>
294<TD>JobTracker is the central location for submitting and
295 tracking MR jobs in a network environment.</TD>
296</TR>
297<TR BGCOLOR="white" CLASS="TableRowColor">
298<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/KeyValueLineRecordReader.html" title="class in org.apache.hadoop.mapred">KeyValueLineRecordReader</A></B></TD>
299<TD>This class treats a line in the input as a key/value pair separated by a
300 separator character.</TD>
301</TR>
302<TR BGCOLOR="white" CLASS="TableRowColor">
303<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/KeyValueTextInputFormat.html" title="class in org.apache.hadoop.mapred">KeyValueTextInputFormat</A></B></TD>
304<TD>An <A HREF="../../../../org/apache/hadoop/mapred/InputFormat.html" title="interface in org.apache.hadoop.mapred"><CODE>InputFormat</CODE></A> for plain text files.</TD>
305</TR>
306<TR BGCOLOR="white" CLASS="TableRowColor">
307<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/LineRecordReader.html" title="class in org.apache.hadoop.mapred">LineRecordReader</A></B></TD>
308<TD><B>Deprecated.</B>&nbsp;<I>Use
309   <A HREF="../../../../org/apache/hadoop/mapreduce/lib/input/LineRecordReader.html" title="class in org.apache.hadoop.mapreduce.lib.input"><CODE>LineRecordReader</CODE></A> instead.</I></TD>
310</TR>
311<TR BGCOLOR="white" CLASS="TableRowColor">
312<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/LineRecordReader.LineReader.html" title="class in org.apache.hadoop.mapred">LineRecordReader.LineReader</A></B></TD>
313<TD><B>Deprecated.</B>&nbsp;<I>Use <A HREF="../../../../org/apache/hadoop/util/LineReader.html" title="class in org.apache.hadoop.util"><CODE>LineReader</CODE></A> instead.</I></TD>
314</TR>
315<TR BGCOLOR="white" CLASS="TableRowColor">
316<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/MapFileOutputFormat.html" title="class in org.apache.hadoop.mapred">MapFileOutputFormat</A></B></TD>
317<TD>An <A HREF="../../../../org/apache/hadoop/mapred/OutputFormat.html" title="interface in org.apache.hadoop.mapred"><CODE>OutputFormat</CODE></A> that writes <A HREF="../../../../org/apache/hadoop/io/MapFile.html" title="class in org.apache.hadoop.io"><CODE>MapFile</CODE></A>s.</TD>
318</TR>
319<TR BGCOLOR="white" CLASS="TableRowColor">
320<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/MapReduceBase.html" title="class in org.apache.hadoop.mapred">MapReduceBase</A></B></TD>
321<TD><B>Deprecated.</B></TD>
322</TR>
323<TR BGCOLOR="white" CLASS="TableRowColor">
324<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/MapReducePolicyProvider.html" title="class in org.apache.hadoop.mapred">MapReducePolicyProvider</A></B></TD>
325<TD><A HREF="../../../../org/apache/hadoop/security/authorize/PolicyProvider.html" title="class in org.apache.hadoop.security.authorize"><CODE>PolicyProvider</CODE></A> for Map-Reduce protocols.</TD>
326</TR>
327<TR BGCOLOR="white" CLASS="TableRowColor">
328<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/MapRunner.html" title="class in org.apache.hadoop.mapred">MapRunner&lt;K1,V1,K2,V2&gt;</A></B></TD>
329<TD>Default <A HREF="../../../../org/apache/hadoop/mapred/MapRunnable.html" title="interface in org.apache.hadoop.mapred"><CODE>MapRunnable</CODE></A> implementation.</TD>
330</TR>
331<TR BGCOLOR="white" CLASS="TableRowColor">
332<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/MultiFileInputFormat.html" title="class in org.apache.hadoop.mapred">MultiFileInputFormat&lt;K,V&gt;</A></B></TD>
333<TD><B>Deprecated.</B>&nbsp;<I>Use <A HREF="../../../../org/apache/hadoop/mapred/lib/CombineFileInputFormat.html" title="class in org.apache.hadoop.mapred.lib"><CODE>CombineFileInputFormat</CODE></A> instead</I></TD>
334</TR>
335<TR BGCOLOR="white" CLASS="TableRowColor">
336<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/MultiFileSplit.html" title="class in org.apache.hadoop.mapred">MultiFileSplit</A></B></TD>
337<TD><B>Deprecated.</B>&nbsp;<I>Use <A HREF="../../../../org/apache/hadoop/mapred/lib/CombineFileSplit.html" title="class in org.apache.hadoop.mapred.lib"><CODE>CombineFileSplit</CODE></A> instead</I></TD>
338</TR>
339<TR BGCOLOR="white" CLASS="TableRowColor">
340<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/OutputCommitter.html" title="class in org.apache.hadoop.mapred">OutputCommitter</A></B></TD>
341<TD><B>Deprecated.</B>&nbsp;<I>Use <A HREF="../../../../org/apache/hadoop/mapreduce/OutputCommitter.html" title="class in org.apache.hadoop.mapreduce"><CODE>OutputCommitter</CODE></A> instead.</I></TD>
342</TR>
343<TR BGCOLOR="white" CLASS="TableRowColor">
344<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/OutputLogFilter.html" title="class in org.apache.hadoop.mapred">OutputLogFilter</A></B></TD>
345<TD>This class filters log files from directory given
346 It doesnt accept paths having _logs.</TD>
347</TR>
348<TR BGCOLOR="white" CLASS="TableRowColor">
349<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/SequenceFileAsBinaryInputFormat.html" title="class in org.apache.hadoop.mapred">SequenceFileAsBinaryInputFormat</A></B></TD>
350<TD>InputFormat reading keys, values from SequenceFiles in binary (raw)
351 format.</TD>
352</TR>
353<TR BGCOLOR="white" CLASS="TableRowColor">
354<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/SequenceFileAsBinaryInputFormat.SequenceFileAsBinaryRecordReader.html" title="class in org.apache.hadoop.mapred">SequenceFileAsBinaryInputFormat.SequenceFileAsBinaryRecordReader</A></B></TD>
355<TD>Read records from a SequenceFile as binary (raw) bytes.</TD>
356</TR>
357<TR BGCOLOR="white" CLASS="TableRowColor">
358<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/SequenceFileAsBinaryOutputFormat.html" title="class in org.apache.hadoop.mapred">SequenceFileAsBinaryOutputFormat</A></B></TD>
359<TD>An <A HREF="../../../../org/apache/hadoop/mapred/OutputFormat.html" title="interface in org.apache.hadoop.mapred"><CODE>OutputFormat</CODE></A> that writes keys, values to
360 <A HREF="../../../../org/apache/hadoop/io/SequenceFile.html" title="class in org.apache.hadoop.io"><CODE>SequenceFile</CODE></A>s in binary(raw) format</TD>
361</TR>
362<TR BGCOLOR="white" CLASS="TableRowColor">
363<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/SequenceFileAsBinaryOutputFormat.WritableValueBytes.html" title="class in org.apache.hadoop.mapred">SequenceFileAsBinaryOutputFormat.WritableValueBytes</A></B></TD>
364<TD>Inner class used for appendRaw</TD>
365</TR>
366<TR BGCOLOR="white" CLASS="TableRowColor">
367<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/SequenceFileAsTextInputFormat.html" title="class in org.apache.hadoop.mapred">SequenceFileAsTextInputFormat</A></B></TD>
368<TD>This class is similar to SequenceFileInputFormat, except it generates SequenceFileAsTextRecordReader
369 which converts the input keys and values to their String forms by calling toString() method.</TD>
370</TR>
371<TR BGCOLOR="white" CLASS="TableRowColor">
372<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/SequenceFileAsTextRecordReader.html" title="class in org.apache.hadoop.mapred">SequenceFileAsTextRecordReader</A></B></TD>
373<TD>This class converts the input keys and values to their String forms by calling toString()
374 method.</TD>
375</TR>
376<TR BGCOLOR="white" CLASS="TableRowColor">
377<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/SequenceFileInputFilter.html" title="class in org.apache.hadoop.mapred">SequenceFileInputFilter&lt;K,V&gt;</A></B></TD>
378<TD>A class that allows a map/red job to work on a sample of sequence files.</TD>
379</TR>
380<TR BGCOLOR="white" CLASS="TableRowColor">
381<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/SequenceFileInputFilter.FilterBase.html" title="class in org.apache.hadoop.mapred">SequenceFileInputFilter.FilterBase</A></B></TD>
382<TD>base class for Filters</TD>
383</TR>
384<TR BGCOLOR="white" CLASS="TableRowColor">
385<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/SequenceFileInputFilter.MD5Filter.html" title="class in org.apache.hadoop.mapred">SequenceFileInputFilter.MD5Filter</A></B></TD>
386<TD>This class returns a set of records by examing the MD5 digest of its
387 key against a filtering frequency <i>f</i>.</TD>
388</TR>
389<TR BGCOLOR="white" CLASS="TableRowColor">
390<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/SequenceFileInputFilter.PercentFilter.html" title="class in org.apache.hadoop.mapred">SequenceFileInputFilter.PercentFilter</A></B></TD>
391<TD>This class returns a percentage of records
392 The percentage is determined by a filtering frequency <i>f</i> using
393 the criteria record# % f == 0.</TD>
394</TR>
395<TR BGCOLOR="white" CLASS="TableRowColor">
396<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/SequenceFileInputFilter.RegexFilter.html" title="class in org.apache.hadoop.mapred">SequenceFileInputFilter.RegexFilter</A></B></TD>
397<TD>Records filter by matching key to regex</TD>
398</TR>
399<TR BGCOLOR="white" CLASS="TableRowColor">
400<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/SequenceFileInputFormat.html" title="class in org.apache.hadoop.mapred">SequenceFileInputFormat&lt;K,V&gt;</A></B></TD>
401<TD><B>Deprecated.</B>&nbsp;<I>Use
402  <A HREF="../../../../org/apache/hadoop/mapreduce/lib/input/SequenceFileInputFormat.html" title="class in org.apache.hadoop.mapreduce.lib.input"><CODE>SequenceFileInputFormat</CODE></A> 
403  instead.</I></TD>
404</TR>
405<TR BGCOLOR="white" CLASS="TableRowColor">
406<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/SequenceFileOutputFormat.html" title="class in org.apache.hadoop.mapred">SequenceFileOutputFormat&lt;K,V&gt;</A></B></TD>
407<TD><B>Deprecated.</B>&nbsp;<I>Use
408   <A HREF="../../../../org/apache/hadoop/mapreduce/lib/output/SequenceFileOutputFormat.html" title="class in org.apache.hadoop.mapreduce.lib.output"><CODE>SequenceFileOutputFormat</CODE></A> 
409   instead.</I></TD>
410</TR>
411<TR BGCOLOR="white" CLASS="TableRowColor">
412<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/SequenceFileRecordReader.html" title="class in org.apache.hadoop.mapred">SequenceFileRecordReader&lt;K,V&gt;</A></B></TD>
413<TD>An <A HREF="../../../../org/apache/hadoop/mapred/RecordReader.html" title="interface in org.apache.hadoop.mapred"><CODE>RecordReader</CODE></A> for <A HREF="../../../../org/apache/hadoop/io/SequenceFile.html" title="class in org.apache.hadoop.io"><CODE>SequenceFile</CODE></A>s.</TD>
414</TR>
415<TR BGCOLOR="white" CLASS="TableRowColor">
416<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/SkipBadRecords.html" title="class in org.apache.hadoop.mapred">SkipBadRecords</A></B></TD>
417<TD>Utility class for skip bad records functionality.</TD>
418</TR>
419<TR BGCOLOR="white" CLASS="TableRowColor">
420<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/TaskAttemptContext.html" title="class in org.apache.hadoop.mapred">TaskAttemptContext</A></B></TD>
421<TD><B>Deprecated.</B>&nbsp;<I>Use <A HREF="../../../../org/apache/hadoop/mapreduce/TaskAttemptContext.html" title="class in org.apache.hadoop.mapreduce"><CODE>TaskAttemptContext</CODE></A>
422   instead.</I></TD>
423</TR>
424<TR BGCOLOR="white" CLASS="TableRowColor">
425<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/TaskAttemptID.html" title="class in org.apache.hadoop.mapred">TaskAttemptID</A></B></TD>
426<TD><B>Deprecated.</B></TD>
427</TR>
428<TR BGCOLOR="white" CLASS="TableRowColor">
429<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/TaskCompletionEvent.html" title="class in org.apache.hadoop.mapred">TaskCompletionEvent</A></B></TD>
430<TD>This is used to track task completion events on
431 job tracker.</TD>
432</TR>
433<TR BGCOLOR="white" CLASS="TableRowColor">
434<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/TaskGraphServlet.html" title="class in org.apache.hadoop.mapred">TaskGraphServlet</A></B></TD>
435<TD>The servlet that outputs svg graphics for map / reduce task
436  statuses</TD>
437</TR>
438<TR BGCOLOR="white" CLASS="TableRowColor">
439<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/TaskID.html" title="class in org.apache.hadoop.mapred">TaskID</A></B></TD>
440<TD><B>Deprecated.</B></TD>
441</TR>
442<TR BGCOLOR="white" CLASS="TableRowColor">
443<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/TaskLog.html" title="class in org.apache.hadoop.mapred">TaskLog</A></B></TD>
444<TD>A simple logger to handle the task-specific user logs.</TD>
445</TR>
446<TR BGCOLOR="white" CLASS="TableRowColor">
447<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/TaskLogAppender.html" title="class in org.apache.hadoop.mapred">TaskLogAppender</A></B></TD>
448<TD>A simple log4j-appender for the task child's
449 map-reduce system logs.</TD>
450</TR>
451<TR BGCOLOR="white" CLASS="TableRowColor">
452<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/TaskLogServlet.html" title="class in org.apache.hadoop.mapred">TaskLogServlet</A></B></TD>
453<TD>A servlet that is run by the TaskTrackers to provide the task logs via http.</TD>
454</TR>
455<TR BGCOLOR="white" CLASS="TableRowColor">
456<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/TaskReport.html" title="class in org.apache.hadoop.mapred">TaskReport</A></B></TD>
457<TD>A report on the state of a task.</TD>
458</TR>
459<TR BGCOLOR="white" CLASS="TableRowColor">
460<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/TaskTracker.html" title="class in org.apache.hadoop.mapred">TaskTracker</A></B></TD>
461<TD>TaskTracker is a process that starts and tracks MR Tasks
462 in a networked environment.</TD>
463</TR>
464<TR BGCOLOR="white" CLASS="TableRowColor">
465<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/TaskTracker.MapOutputServlet.html" title="class in org.apache.hadoop.mapred">TaskTracker.MapOutputServlet</A></B></TD>
466<TD>This class is used in TaskTracker's Jetty to serve the map outputs
467 to other nodes.</TD>
468</TR>
469<TR BGCOLOR="white" CLASS="TableRowColor">
470<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/TextInputFormat.html" title="class in org.apache.hadoop.mapred">TextInputFormat</A></B></TD>
471<TD><B>Deprecated.</B>&nbsp;<I>Use <A HREF="../../../../org/apache/hadoop/mapreduce/lib/input/TextInputFormat.html" title="class in org.apache.hadoop.mapreduce.lib.input"><CODE>TextInputFormat</CODE></A>
472  instead.</I></TD>
473</TR>
474<TR BGCOLOR="white" CLASS="TableRowColor">
475<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/TextOutputFormat.html" title="class in org.apache.hadoop.mapred">TextOutputFormat&lt;K,V&gt;</A></B></TD>
476<TD><B>Deprecated.</B>&nbsp;<I>Use
477   <A HREF="../../../../org/apache/hadoop/mapreduce/lib/output/TextOutputFormat.html" title="class in org.apache.hadoop.mapreduce.lib.output"><CODE>TextOutputFormat</CODE></A> instead.</I></TD>
478</TR>
479<TR BGCOLOR="white" CLASS="TableRowColor">
480<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/TextOutputFormat.LineRecordWriter.html" title="class in org.apache.hadoop.mapred">TextOutputFormat.LineRecordWriter&lt;K,V&gt;</A></B></TD>
481<TD>&nbsp;</TD>
482</TR>
483</TABLE>
484&nbsp;
485
486<P>
487
488<TABLE BORDER="1" WIDTH="100%" CELLPADDING="3" CELLSPACING="0" SUMMARY="">
489<TR BGCOLOR="#CCCCFF" CLASS="TableHeadingColor">
490<TH ALIGN="left" COLSPAN="2"><FONT SIZE="+2">
491<B>Enum Summary</B></FONT></TH>
492</TR>
493<TR BGCOLOR="white" CLASS="TableRowColor">
494<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/JobClient.TaskStatusFilter.html" title="enum in org.apache.hadoop.mapred">JobClient.TaskStatusFilter</A></B></TD>
495<TD>&nbsp;</TD>
496</TR>
497<TR BGCOLOR="white" CLASS="TableRowColor">
498<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/JobHistory.Keys.html" title="enum in org.apache.hadoop.mapred">JobHistory.Keys</A></B></TD>
499<TD>Job history files contain key="value" pairs, where keys belong to this enum.</TD>
500</TR>
501<TR BGCOLOR="white" CLASS="TableRowColor">
502<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/JobHistory.RecordTypes.html" title="enum in org.apache.hadoop.mapred">JobHistory.RecordTypes</A></B></TD>
503<TD>Record types are identifiers for each line of log in history files.</TD>
504</TR>
505<TR BGCOLOR="white" CLASS="TableRowColor">
506<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/JobHistory.Values.html" title="enum in org.apache.hadoop.mapred">JobHistory.Values</A></B></TD>
507<TD>This enum contains some of the values commonly used by history log events.</TD>
508</TR>
509<TR BGCOLOR="white" CLASS="TableRowColor">
510<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/JobPriority.html" title="enum in org.apache.hadoop.mapred">JobPriority</A></B></TD>
511<TD>Used to describe the priority of the running job.</TD>
512</TR>
513<TR BGCOLOR="white" CLASS="TableRowColor">
514<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/JobTracker.State.html" title="enum in org.apache.hadoop.mapred">JobTracker.State</A></B></TD>
515<TD>&nbsp;</TD>
516</TR>
517<TR BGCOLOR="white" CLASS="TableRowColor">
518<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/TaskCompletionEvent.Status.html" title="enum in org.apache.hadoop.mapred">TaskCompletionEvent.Status</A></B></TD>
519<TD>&nbsp;</TD>
520</TR>
521<TR BGCOLOR="white" CLASS="TableRowColor">
522<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/TaskLog.LogName.html" title="enum in org.apache.hadoop.mapred">TaskLog.LogName</A></B></TD>
523<TD>The filter for userlogs.</TD>
524</TR>
525<TR BGCOLOR="white" CLASS="TableRowColor">
526<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/TIPStatus.html" title="enum in org.apache.hadoop.mapred">TIPStatus</A></B></TD>
527<TD>The states of a <CODE>TaskInProgress</CODE> as seen by the JobTracker.</TD>
528</TR>
529</TABLE>
530&nbsp;
531
532<P>
533
534<TABLE BORDER="1" WIDTH="100%" CELLPADDING="3" CELLSPACING="0" SUMMARY="">
535<TR BGCOLOR="#CCCCFF" CLASS="TableHeadingColor">
536<TH ALIGN="left" COLSPAN="2"><FONT SIZE="+2">
537<B>Exception Summary</B></FONT></TH>
538</TR>
539<TR BGCOLOR="white" CLASS="TableRowColor">
540<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/FileAlreadyExistsException.html" title="class in org.apache.hadoop.mapred">FileAlreadyExistsException</A></B></TD>
541<TD>Used when target file already exists for any operation and
542 is not configured to be overwritten.</TD>
543</TR>
544<TR BGCOLOR="white" CLASS="TableRowColor">
545<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/InvalidFileTypeException.html" title="class in org.apache.hadoop.mapred">InvalidFileTypeException</A></B></TD>
546<TD>Used when file type differs from the desired file type.</TD>
547</TR>
548<TR BGCOLOR="white" CLASS="TableRowColor">
549<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/InvalidInputException.html" title="class in org.apache.hadoop.mapred">InvalidInputException</A></B></TD>
550<TD>This class wraps a list of problems with the input, so that the user
551 can get a list of problems together instead of finding and fixing them one
552 by one.</TD>
553</TR>
554<TR BGCOLOR="white" CLASS="TableRowColor">
555<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/InvalidJobConfException.html" title="class in org.apache.hadoop.mapred">InvalidJobConfException</A></B></TD>
556<TD>This exception is thrown when jobconf misses some mendatory attributes
557 or value of some attributes is invalid.</TD>
558</TR>
559<TR BGCOLOR="white" CLASS="TableRowColor">
560<TD WIDTH="15%"><B><A HREF="../../../../org/apache/hadoop/mapred/JobTracker.IllegalStateException.html" title="class in org.apache.hadoop.mapred">JobTracker.IllegalStateException</A></B></TD>
561<TD>A client tried to submit a job before the Job Tracker was ready.</TD>
562</TR>
563</TABLE>
564&nbsp;
565
566<P>
567<A NAME="package_description"><!-- --></A><H2>
568Package org.apache.hadoop.mapred Description
569</H2>
570
571<P>
572<p>A software framework for easily writing applications which process vast
573amounts of data (multi-terabyte data-sets) parallelly on large clusters
574(thousands of nodes) built of commodity hardware in a reliable, fault-tolerant
575manner.</p>
576
577<p>A Map-Reduce <i>job</i> usually splits the input data-set into independent
578chunks which processed by <i>map</i> tasks in completely parallel manner,
579followed by <i>reduce</i> tasks which aggregating their output. Typically both
580the input and the output of the job are stored in a
581<A HREF="../../../../org/apache/hadoop/fs/FileSystem.html" title="class in org.apache.hadoop.fs"><CODE>FileSystem</CODE></A>. The framework takes care of monitoring
582tasks and re-executing failed ones. Since, usually, the compute nodes and the
583storage nodes are the same i.e. Hadoop's Map-Reduce framework and Distributed
584FileSystem are running on the same set of nodes, tasks are effectively scheduled
585on the nodes where data is already present, resulting in very high aggregate
586bandwidth across the cluster.</p>
587
588<p>The Map-Reduce framework operates exclusively on <tt>&lt;key, value&gt;</tt> 
589pairs i.e. the input to the job is viewed as a set of <tt>&lt;key, value&gt;</tt>
590pairs and the output as another, possibly different, set of
591<tt>&lt;key, value&gt;</tt> pairs. The <tt>key</tt>s and <tt>value</tt>s have to
592be serializable as <A HREF="../../../../org/apache/hadoop/io/Writable.html" title="interface in org.apache.hadoop.io"><CODE>Writable</CODE></A>s and additionally the
593<tt>key</tt>s have to be <A HREF="../../../../org/apache/hadoop/io/WritableComparable.html" title="interface in org.apache.hadoop.io"><CODE>WritableComparable</CODE></A>s in
594order to facilitate grouping by the framework.</p>
595
596<p>Data flow:</p>
597<pre>
598                                (input)
599                                <tt>&lt;k1, v1&gt;</tt>
600       
601                                   |
602                                   V
603       
604                                  <b>map</b>
605       
606                                   |
607                                   V
608
609                                <tt>&lt;k2, v2&gt;</tt>
610       
611                                   |
612                                   V
613       
614                                <b>combine</b>
615       
616                                   |
617                                   V
618       
619                                <tt>&lt;k2, v2&gt;</tt>
620       
621                                   |
622                                   V
623       
624                                 <b>reduce</b>
625       
626                                   |
627                                   V
628       
629                                <tt>&lt;k3, v3&gt;</tt>
630                                (output)
631</pre>
632
633<p>Applications typically implement
634<A HREF="../../../../org/apache/hadoop/mapred/Mapper.html#map(K1, V1, org.apache.hadoop.mapred.OutputCollector, org.apache.hadoop.mapred.Reporter)"><CODE>Mapper.map(Object, Object, OutputCollector, Reporter)</CODE></A> 
635and
636<A HREF="../../../../org/apache/hadoop/mapred/Reducer.html#reduce(K2, java.util.Iterator, org.apache.hadoop.mapred.OutputCollector, org.apache.hadoop.mapred.Reporter)"><CODE>Reducer.reduce(Object, Iterator, OutputCollector, Reporter)</CODE></A> 
637methods.  The application-writer also specifies various facets of the job such
638as input and output locations, the <tt>Partitioner</tt>, <tt>InputFormat</tt> 
639&amp; <tt>OutputFormat</tt> implementations to be used etc. as
640a <A HREF="../../../../org/apache/hadoop/mapred/JobConf.html" title="class in org.apache.hadoop.mapred"><CODE>JobConf</CODE></A>. The client program,
641<A HREF="../../../../org/apache/hadoop/mapred/JobClient.html" title="class in org.apache.hadoop.mapred"><CODE>JobClient</CODE></A>, then submits the job to the framework
642and optionally monitors it.</p>
643
644<p>The framework spawns one map task per
645<A HREF="../../../../org/apache/hadoop/mapred/InputSplit.html" title="interface in org.apache.hadoop.mapred"><CODE>InputSplit</CODE></A> generated by the
646<A HREF="../../../../org/apache/hadoop/mapred/InputFormat.html" title="interface in org.apache.hadoop.mapred"><CODE>InputFormat</CODE></A> of the job and calls
647<A HREF="../../../../org/apache/hadoop/mapred/Mapper.html#map(K1, V1, org.apache.hadoop.mapred.OutputCollector, org.apache.hadoop.mapred.Reporter)"><CODE>Mapper.map(Object, Object, OutputCollector, Reporter)</CODE></A> 
648with each &lt;key, value&gt; pair read by the
649<A HREF="../../../../org/apache/hadoop/mapred/RecordReader.html" title="interface in org.apache.hadoop.mapred"><CODE>RecordReader</CODE></A> from the <tt>InputSplit</tt> for
650the task. The intermediate outputs of the maps are then grouped by <tt>key</tt>s
651and optionally aggregated by <i>combiner</i>. The key space of intermediate
652outputs are paritioned by the <A HREF="../../../../org/apache/hadoop/mapred/Partitioner.html" title="interface in org.apache.hadoop.mapred"><CODE>Partitioner</CODE></A>, where
653the number of partitions is exactly the number of reduce tasks for the job.</p>
654
655<p>The reduce tasks fetch the sorted intermediate outputs of the maps, via http,
656merge the &lt;key, value&gt; pairs and call
657<A HREF="../../../../org/apache/hadoop/mapred/Reducer.html#reduce(K2, java.util.Iterator, org.apache.hadoop.mapred.OutputCollector, org.apache.hadoop.mapred.Reporter)"><CODE>Reducer.reduce(Object, Iterator, OutputCollector, Reporter)</CODE></A> 
658for each &lt;key, list of values&gt; pair. The output of the reduce tasks' is
659stored on the <tt>FileSystem</tt> by the
660<A HREF="../../../../org/apache/hadoop/mapred/RecordWriter.html" title="interface in org.apache.hadoop.mapred"><CODE>RecordWriter</CODE></A> provided by the
661<A HREF="../../../../org/apache/hadoop/mapred/OutputFormat.html" title="interface in org.apache.hadoop.mapred"><CODE>OutputFormat</CODE></A> of the job.</p>
662
663<p>Map-Reduce application to perform a distributed <i>grep</i>:</p>
664<pre><tt>
665public class Grep extends Configured implements Tool {
666
667  // <i>map: Search for the pattern specified by 'grep.mapper.regex' &amp;</i>
668  //      <i>'grep.mapper.regex.group'</i>
669
670  class GrepMapper&lt;K, Text&gt; 
671  extends MapReduceBase  implements Mapper&lt;K, Text, Text, LongWritable&gt; {
672
673    private Pattern pattern;
674    private int group;
675
676    public void configure(JobConf job) {
677      pattern = Pattern.compile(job.get("grep.mapper.regex"));
678      group = job.getInt("grep.mapper.regex.group", 0);
679    }
680
681    public void map(K key, Text value,
682                    OutputCollector&lt;Text, LongWritable&gt; output,
683                    Reporter reporter)
684    throws IOException {
685      String text = value.toString();
686      Matcher matcher = pattern.matcher(text);
687      while (matcher.find()) {
688        output.collect(new Text(matcher.group(group)), new LongWritable(1));
689      }
690    }
691  }
692
693  // <i>reduce: Count the number of occurrences of the pattern</i>
694
695  class GrepReducer&lt;K&gt; extends MapReduceBase
696  implements Reducer&lt;K, LongWritable, K, LongWritable&gt; {
697
698    public void reduce(K key, Iterator&lt;LongWritable&gt; values,
699                       OutputCollector&lt;K, LongWritable&gt; output,
700                       Reporter reporter)
701    throws IOException {
702
703      // sum all values for this key
704      long sum = 0;
705      while (values.hasNext()) {
706        sum += values.next().get();
707      }
708
709      // output sum
710      output.collect(key, new LongWritable(sum));
711    }
712  }
713 
714  public int run(String[] args) throws Exception {
715    if (args.length &lt; 3) {
716      System.out.println("Grep &lt;inDir&gt; &lt;outDir&gt; &lt;regex&gt; [&lt;group&gt;]");
717      ToolRunner.printGenericCommandUsage(System.out);
718      return -1;
719    }
720
721    JobConf grepJob = new JobConf(getConf(), Grep.class);
722   
723    grepJob.setJobName("grep");
724
725    FileInputFormat.setInputPaths(grepJob, new Path(args[0]));
726    FileOutputFormat.setOutputPath(grepJob, args[1]);
727
728    grepJob.setMapperClass(GrepMapper.class);
729    grepJob.setCombinerClass(GrepReducer.class);
730    grepJob.setReducerClass(GrepReducer.class);
731
732    grepJob.set("mapred.mapper.regex", args[2]);
733    if (args.length == 4)
734      grepJob.set("mapred.mapper.regex.group", args[3]);
735
736    grepJob.setOutputFormat(SequenceFileOutputFormat.class);
737    grepJob.setOutputKeyClass(Text.class);
738    grepJob.setOutputValueClass(LongWritable.class);
739
740    JobClient.runJob(grepJob);
741
742    return 0;
743  }
744
745  public static void main(String[] args) throws Exception {
746    int res = ToolRunner.run(new Configuration(), new Grep(), args);
747    System.exit(res);
748  }
749
750}
751</tt></pre>
752
753<p>Notice how the data-flow of the above grep job is very similar to doing the
754same via the unix pipeline:</p>
755
756<pre>
757cat input/*   |   grep   |   sort    |   uniq -c   &gt;   out
758</pre>
759
760<pre>
761      input   |    map   |  shuffle  |   reduce    &gt;   out
762</pre>
763
764<p>Hadoop Map-Reduce applications need not be written in
765Java<small><sup>TM</sup></small> only.
766<a href="../streaming/package-summary.html">Hadoop Streaming</a> is a utility
767which allows users to create and run jobs with any executables (e.g. shell
768utilities) as the mapper and/or the reducer.
769<a href="pipes/package-summary.html">Hadoop Pipes</a> is a
770<a href="http://www.swig.org/">SWIG</a>-compatible <em>C++ API</em> to implement
771Map-Reduce applications (non JNI<small><sup>TM</sup></small> based).</p>
772
773<p>See <a href="http://labs.google.com/papers/mapreduce.html">Google's original
774Map/Reduce paper</a> for background information.</p>
775
776<p><i>Java and JNI are trademarks or registered trademarks of
777Sun Microsystems, Inc. in the United States and other countries.</i></p>
778<P>
779
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