The jar in the command line might only be the jar to submit the map-reduce job, rather than the jar contains the Mapper and Reducer which will be transferred to different node.
What the hadoop jar your-jar really did, is setting the classpath and other related environment, and run the main method in your-jar. You might have a different map-reduce-jar in the classpath which contains the real mapper and reducer used to do the job. Best wishes, Stanley Xu On Fri, Feb 25, 2011 at 7:23 AM, Mark Kerzner <markkerz...@gmail.com> wrote: > Hi, this call, > > job.setJarByClass > > tells Hadoop which jar to use. But we also tell Hadoop which jar to use on > the command line, > > hadoop jar your-jar parameters > > Why do we need this in both places? > > Thank you, > Mark >
