Question

Point out the correct statement.

(a) The framework groups Reducer inputs by keys

(b) The shuffle and sort phases occur simultaneously i.e. while outputs are being fetched they are merged

(c) Since JobConf.setOutputKeyComparatorClass(Class) can be used to control how intermediate keys are grouped, these can be used in conjunction to simulate secondary sort on values

(d) All of the mentioned

This question was posed to me in an interview for internship.

The query is from Java Interface in portion HDFS – Hadoop Distributed File System of Hadoop

Answer 1

The correct answer is (d) All of the mentioned

For explanation I would say: If equivalence rules for keys while grouping the intermediates are different from those for grouping keys before reduction, then one may specify a Comparator.