[Lucene-hadoop Wiki] Update of "WordCount" by OwenOMalley

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http://wiki.apache.org/lucene-hadoop/WordCount

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  '''WordCount''' example reads text files and counts how often words occur.  The input is text files and the output is text files, each line of which contains a word and the count of how often it occured, separated by a tab.
  
- Each mapper takes a line as input and breaks it into words. It then emits word and 1 pair. Each reducer sums the frequencies of a word.
+ Each mapper takes a line as input and breaks it into words. It then emits a key/value pair of the word and 1. Each reducer sums the counts for each word and emits a single key/value with the word and sum.
  
- The output of maps are locally summed by setting the comibiner class to be the same as the Reducer class.
+ As an optimization, the reducer is also used as a combiner on the map outputs. This reduces the amount of data sent across the network by combining each word into a single record.
  
  To run the example, the command syntax is[[BR]]
- bin/hadoop org.apache.hadoop.examples.WordCount [-m <#maps>] [-r <#reducers>] <in-dir> <out-dir>
+ bin/hadoop jar build/hadoop-*-examples.jar wordcount [-m <#maps>] [-r <#reducers>] <in-dir> <out-dir>