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courses:mapreduce-tutorial:step-8 [2012/01/25 15:54]
straka 		courses:mapreduce-tutorial:step-8 [2012/01/25 18:37]
straka
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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.
 +
 +===== The order of keys during reduce =====
 +It is guaranteed that every reducer processes the keys in //ascending order//.
 +
 +On the other hand, when processing one key, the order of its values is undefined.
  
 ===== Example ===== ===== 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.+Run a MR job on '/home/straka/wiki/cs-text-medium', which creates an ascending list of unique article names and at the same time an ascending list of unique words.
  
 {{:courses:mapreduce-tutorial:step-8-solution.txt|Solution.pl}} {{:courses:mapreduce-tutorial:step-8-solution.txt|Solution.pl}}

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