Hadoop Map-Reduce

Hadoop is Apache's free and open source implementation of Map-Reduce.

Overview
The Hadoop Map-Reduce framework has a master/slave architecture. It has a single master server or jobtracker and several slave servers or tasktrackers, one per node in the cluster. The jobtracker is the point of interaction between users and the framework. Users submit map/reduce jobs to the jobtracker, which puts them in a queue of pending jobs and executes them on a first-come/first-served basis. The jobtracker manages the assignment of map and reduce tasks to the tasktrackers. The tasktrackers execute tasks upon instruction from the jobtracker and also handle data motion between the map and reduce phases.