What is the functionality of JobTracker in Hadoop? How many instances of a JobTracker run on Hadoop cluster?
JobTracker is a giant service which is used to submit and track MapReduce jobs in Hadoop. Only one JobTracker process runs on any Hadoop cluster. JobTracker runs it within its own JVM process.
Functionalities of JobTracker in Hadoop:
- When client application submits jobs to the JobTracker, the JobTracker talks to the NameNode to find the location of the data.
- It locates TaskTracker nodes with available slots for data.
- It assigns the work to the chosen TaskTracker nodes.
- The TaskTracker nodes are responsible to notify the JobTracker when a task fails and then JobTracker decides what to do then. It may resubmit the task on another node or it may mark that task to avoid.