Hadoop has two major components:
– the distributed filesystem component, the main example of which is the Hadoop
Distributed File System, though other file systems are supported.
– the MapReduce component, which is a framework for performing calculations on
the data in the distributed file system.
HDFS was based on a paper Google published about their Google File System,
Hadoop’s MapReduce is inspired by a paper Google published on the MapReduce
A MapReduce program consists of two types of transformations that can be applied
to data any number of times – a map transformation and a reduce transformation.