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courses:mapreduce-tutorial:step-8 [2012/01/25 15:16]
straka 		courses:mapreduce-tutorial:step-8 [2012/01/25 15:54]
straka
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 To use multiple reducers, the MR job must be executed by a cluster (even with one computer), not locally. The number of reducers is specified by ''-r'' flag: To use multiple reducers, the MR job must be executed by a cluster (even with one computer), not locally. The number of reducers is specified by ''-r'' flag:
-  perl script.pl [-j cluster_master | -c cluster_size [-w sec_to_wait]] [-r number_of_reducers]+  perl script.pl run [-jt cluster_master | -c cluster_size [-w sec_to_wait]] [-r number_of_reducers]
  
 ==== Partitioning ==== ==== Partitioning ====
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 A MR job must have a reducer if it specifies a partitioner. Also, the partitioner is not called if there is only one reducer. A MR job must have a reducer if it specifies a partitioner. Also, the partitioner is not called if there is only one reducer.
  
 +===== Example =====
 +
 +Run a MR job on '/home/straka/wiki/cs-text-medium', which creates a list of unique article names and at the same time list of unique words.
 +
 +{{:courses:mapreduce-tutorial:step-8-solution.txt|Solution.pl}}

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