mapreduce - Hadoop Basics:Number of map tasks mappers reduce tasks reducers -

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what difference between mapper , map task? similarly, reducer , reduce task? also, how number of mappers,maptasks,reducers,reducetasks determined during execution of mapreduce task? give interrelationships between them if there any.

simply map task instance of mapper. mapper , reducer methods in mapreduce jobs.

when run mapreduce job, number of map tasks spawned depends on number blocks(number of blocks depend on input splits) in input. number of reduce tasks can specified in mapreduce driver code. either can specified setting property mapred.reduce.tasks in job configuration object or org.apache.hadoop.mapreduce.job#setnumreducetasks(int reducercount); method can used.

in old jobconf api setnummaptasks() method there. setnummaptasks() method removed in new api org.apache.hadoop.mapreduce.jobwith intension of number of mappers should calculated based on input splits.


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