What are the comparators in Mapreduce ?

In Mapreduce framework, during sorting phase, map output keys are compared with each other.
Hadoop provides RawComparator which is an extension of java’s Comparator for comparing binary stream data directly without de-serializing it into objects, thereby avoiding overhead of creation of objects.

Java

package org.apache.hadoop.io;
import java.util.Comparator;

public interface RawComparator<T> extends Comparator<T>
{
public int compare(byte[] b1, int s1, int l1, byte[] b2, int s2, int l2);
}

The comparator for IntWritables implements the raw compare() method by reading an integer from each of the byte arrays b1 and b2 and comparing them directly, from the given start positions ( s1 and s2 ) and lengths ( l1 and l2 ).