- It is not about speed-of-thought response times
- It is not real-time warehousing
- Hadoop Distributed File System
- Programming paradigm – Map Reduce pattern
- Hadoop Common
- Client applications submit jobs to the Job tracker.
- The JobTracker talks to the NameNode to determine the location of the data
- The JobTracker locates TaskTracker nodes with available slots at or near the data
- The JobTracker submits the work to the chosen TaskTracker nodes.
- The TaskTracker nodes are monitored. If they do not submit heartbeat signals often enough, they are deemed to have failed and the work is scheduled on a different TaskTracker.
- A TaskTracker will notify the JobTracker when a task fails. The JobTracker decides what to do then: it may resubmit the job elsewhere, it may mark that specific record as something to avoid, and it may may even blacklist the TaskTracker as unreliable.
- When the work is completed, the JobTracker updates its status.
- Client applications can poll the JobTracker for information.