To run Hadoop and get a maximum performance, it needs to be configured correctly. But the question is how to do that. Well, based on our experiences, we can say that there is not one single answer to this question. The experiences gave us a clear indication that the Hadoop framework should be adapted for the cluster it is running on and sometimes also to the job.

In order to configure your cluster correctly, we recommend running a Hadoop job(s) the first time with its default configuration to get a baseline (see Chapter 3, Detecting System Bottlenecks). Then, you will check the resource's weakness (if it exists) by analyzing the job history logfiles and report the results (measured time it took to run the jobs). After that, iteratively, you will tune your Hadoop configuration and re-run the job until you get the configuration that fits your business needs.

The number of mappers and reducer tasks that a job should use is important. Picking the right amount...