You can set the number of reducers used in any hadoop job from the command line by using -Dmapred.reduce.tasks=XX.
e.g. hadoop jar hadoop-mapreduce-examples.jar terasort -Dmapred.reduce.tasks=10 /terasort-input /terasort-output
You can set the number of reducers used in any hadoop job from the command line by using -Dmapred.reduce.tasks=XX.
e.g. hadoop jar hadoop-mapreduce-examples.jar terasort -Dmapred.reduce.tasks=10 /terasort-input /terasort-output