MapReduce Cloud Computing Question:

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When do reducers play their role in a mapreduce task?

Cloud Computing - MapReduce Interview Question
Cloud Computing - MapReduce Interview Question

Answer:

The reducers in a mapreduce job do not begin before all the map jobs are completed. Once all the map jobs are completed the reducers begin copying the intermediate key-value pairs from the mappers. Overall reducers start working as soon as the mappers are ready with key-value pairs.

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