One of the things that bothers me about the JobTracker is that it is running user code when it creates the FileSplits. In the long term this puts the JobTracker JVM at risk due to errors in the user code.
The JobTracker uses the InputFormat to create a set of tasks that it then schedules. The task creation does not need to happen at the JobTracker. If we allowed the clients to create the set of tasks, the JobTracker would not need to load and run any user generated code. It would also remove some of the processing load from the JobTracker. On the downside it does greatly increase the amount of information sent to the JobTracker when a job is submitted. ben
