What happens in a MapReduce job when you set the number of reducers to one?
A. A single reducer gathers and processes all the output from all the mappers. The output is written in as many separate files as there are mappers.
B. A single reducer gathers and processes all the output from all the mappers. The output is written to a single file in HDFS.
C. Setting the number of reducers to one creates a processing bottleneck, and since the number of reducers as specified by the programmer is used as a reference value only, the MapReduce runtime provides a default setting for the number of reducers.
D. Setting the number of reducers to one is invalid, and an exception is thrown.
Answer: A
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