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What are the core methods of a Reducer? 

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The 3 core methods of a reducer are –


1)setup () – This method of the reducer is used for configuring various parameters like the input data size, distributed cache, heap size, etc.


Function Definition- public void setup (context)


2)reduce () it is heart of the reducer which is called once per key with the associated reduce task.


Function Definition -public void reduce (Key,Value,context)


3)cleanup () - This method is called only once at the end of reduce task for clearing all the temporary files.


Function Definition -public void cleanup (context)