Apache-Hadoop-Developer Free Dumps Study Materials
Question 3: All keys used for intermediate output from mappers must:
A. Implement a splittable compression algorithm.
B. Be a subclass of FileInputFormat.
C. Implement WritableComparable.
D. Override isSplitable.
E. Implement a comparator for speedy sorting.
Correct Answer: C
Explanation:
The MapReduce framework operates exclusively on <key, value> pairs, that is, the framework views
the input to the job as a set of <key, value> pairs and produces a set of <key, value> pairs as the
output of the job, conceivably of different types.
The key and value classes have to be serializable by the framework and hence need to implement the
Writable interface. Additionally, the key classes have to implement the WritableComparable interface
to facilitate sorting by the framework.
Reference: MapReduce Tutorial