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Which Hadoop Phase Sorts Mapper Output by Keys Before Reducing?
Learn how the shuffle and sort phase in Hadoop MapReduce ensures that all intermediate data is grouped and ordered by keys before reaching reducers, improving data processing and output organization.
Question
Which step ensures Hadoop output is arranged according to keys by default?
A. The shuffle and sort phase
B. Node replication
C. Input split creation
D. Combiner execution
Answer
A. The shuffle and sort phase
Explanation
The shuffle and sort phase in Hadoop MapReduce automatically organizes output data based on the key values before it reaches the reducer. During this phase, all intermediate key-value pairs produced by the mappers are transferred to the reducers. Hadoop groups values by keys and sorts them in ascending order by default, ensuring that the reducer receives data in a structured and sequential manner. This is crucial for efficient data aggregation, joining, and summarization tasks performed in the reduce step.