What are the differences between Sort Comparator and Group Comparator in Hadoop?

Question

What are the differences between Sort Comparator and Group Comparator in Hadoop?

Answer 1

Group Comparator decides which map output keys will be united(grouped) into one key, and of course all collections of values will be grouped too. Usually it takes a first key as the only one for summary collection.

SortComparator decides how keys will be sorted in input of reduce. By default it uses natural ordering.