For each input key-value pair, mappers can emit:

For each input key-value pair, mappers can emit:
A . As many intermediate key-value pairs as designed. There are no restrictions on the types of those key-value pairs (i.e., they can be heterogeneous).
B . As many intermediate key-value pairs as designed, but they cannot be of the same type as the input key-value pair.
C . One intermediate key-value pair, of a different type.
D . One intermediate key-value pair, but of the same type.
E . As many intermediate key-value pairs as designed, as long as all the keys have the same types and all the values have the same type.

View Answer

Answer: E

Explanation:

Mapper maps input key/value pairs to a set of intermediate key/value pairs.

Maps are the individual tasks that transform input records into intermediate records. The transformed intermediate records do not need to be of the same type as the input records. A given input pair may map to zero or many output pairs.

Reference: Hadoop Map-Reduce Tutorial