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HADOOP - When is the reducers are started in a MapReduce job?




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asked SRVMTrainings February 14, 2014 06:01 AM  

When is the reducers are started in a MapReduce job?


           

5 Answers



 
answered By Akshay Singh   0  
This answer is pending moderator approval Every MapReduce Jobs goes through - fllowing phases:
-Input Split
-Map Phase
-Suffle and Sort Phase
-Reduce Phase
-Output phase,

So the reducer comes in role only after the Suffle and Sort phase.
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answered By   0  
A MapReduce partitioner makes sure that all the value of a single key goes to the same reducer, thus allows evenly distribution of the map output over the reducers. It redirects the mapper output to the reducer by determining which reducer is responsible for a particular key,
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answered By   0  

First mapper take the input and provide the output to reducer , which start the reducer process..
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answered By krishnaveni   0  
After receiving the mapper output then only it will start the process..
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answered By   0  
In a MapReducer job Reducer do not start executing the reduce method untill all the Map jobs have been completed.

Reducers start copying intermediate key-value pairs from the mapper as soon as they are available.
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answered By   0  
When all the mappers are completed map jobs.
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