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HADOOP - What is next step after Mapper or MapTask?




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asked SRVMTrainings August 9, 2013 07:24 AM  

What is next step after Mapper or MapTask?


           

2 Answers



 
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After Map task , Reducer task starts. 

Reducer has 3 primary phases:
Shuffle, sort & Reduce.

Reducer combines the multiple outputs of Mapper (Map Task) to one standard output.
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answered By   0  
After Map Task, sorting and shuffling phase coming to the picture, In this phase sorted and merge the data, once complete the sort and shuffling phase reducer will coming to the picture. 
mapper output: (hi,1) (hi,1) (hi,1) (hi,1) (what,2) (what,3) (what,3)
Sort and Shuffle: (hi, {1,1,1,1,}),(what,{2,3,3,}).................)
Reducer Input: (hi, {1,1,1,1,}),(what,{2,3,3,}).................)
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