How to set the number of Map Reduce tasks

Question

I am executing a MapReduce task. I have specified the mapred.map.tasks property to 20 & mapred.reduce.tasks to 0. But still I am getting a different number of mapper & reducer tasks. My command is

hadoop jar Example.jar Example abc.txt Result \ -D mapred.map.tasks = 20 \ -D mapred.reduce.tasks =0

Can anyone help me in understanding what is the problem here & how can I fix this?

Answer 1

The map tasks created for a job is equal to the number of the of input splits created. For each input split a map job is created. The mapred.map.tasks property hints InputFormat about the map tasks created.

For the reduce tasks you have to remove the extra space after -D.