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CCD-410 · Question #58
CCD-410 Question #58: Real Exam Question with Answer & Explanation
The correct answer is B. Reducers start copying intermediate key-value pairs from each Mapper as soon as it has completed.. In a MapReduce job reducers do not start executing the reduce method until the all Map jobs have completed. Reducers start copying intermediate key-value pairs from the mappers as soon as they are available. The programmer defined reduce method is called only after all the mapper
Question
Determine which best describes when the reduce method is first called in a MapReduce job?
Options
- AReducers start copying intermediate key-value pairs from each Mapper as soon as it has completed.
- BReducers start copying intermediate key-value pairs from each Mapper as soon as it has completed.
- CReduce methods and map methods all start at the beginning of a job, in order to provide optimal
- DReducers start copying intermediate key-value pairs from each Mapper as soon as it has completed.
Explanation
- In a MapReduce job reducers do not start executing the reduce method until the all Map jobs have completed. Reducers start copying intermediate key-value pairs from the mappers as soon as they are available. The programmer defined reduce method is called only after all the mappers * Reducers start copying intermediate key-value pairs from the mappers as soon as they are available. The progress calculation also takes in account the processing of data transfer which is done by reduce process, therefore the reduce progress starts showing up as soon as any intermediate key-value pair for a mapper is available to be transferred to reducer. Though the reducer progress is updated still the programmer defined reduce method is called only after all the mappers have finished.
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