Cloudera
CCD-410 · Question #7
In a MapReduce job, the reducer receives all values associated with same key. Which statement best describes the ordering of these values?
The correct answer is B. The values are arbitrarily ordered, and the ordering may vary from run to run of the same MapReduce job. Input to the Reducer is the sorted output of the mappers. The framework calls the application's Reduce function once for each unique key in the sorted For the given sample input the first map emits: The second map emits:
Developing with Apache Spark Core
Question
In a MapReduce job, the reducer receives all values associated with same key. Which statement best describes the ordering of these values?
Options
- AThe values are in sorted order.
- BThe values are arbitrarily ordered, and the ordering may vary from run to run of the same MapReduce job.
- CThe values are arbitrary ordered, but multiple runs of the same MapReduce job will always have the same
- DSince the values come from mapper outputs, the reducers will receive contiguous sections of sorted values.
How the community answered
(36 responses)- A3% (1)
- B78% (28)
- C14% (5)
- D6% (2)
Explanation
- Input to the Reducer is the sorted output of the mappers. * The framework calls the application's Reduce function once for each unique key in the sorted For the given sample input the first map emits: The second map emits:
Topics
#reducer#value ordering#shuffle phase#MapReduce behavior
Community Discussion
No community discussion yet for this question.