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courses:mapreduce-tutorial:step-8 [2012/01/25 14:47]
straka 		courses:mapreduce-tutorial:step-8 [2012/01/25 14:54]
straka
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 ====== MapReduce Tutorial : Multiple mappers, reducers and partitioning ====== ====== MapReduce Tutorial : Multiple mappers, reducers and partitioning ======
  
 +In order to achieve parallelism, mappers and reducers must be executed in parallel.
 +
 +===== Multiple mappers =====
 +The number of mappers is determined automatically according to input files sizes. Every input file is divided into //splits//. The default split size is 32MB. Every file split is then executed by a different mapper.
 +
 +The size of file split can be overridden by ''mapred.min.split.size'' and ''maperd.max.split.size''. See the next tutorial step for how to set these flags.
 +
 +===== Multiple reducers =====
  
  

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