Earning Points. Starwood's Preferred Guest program is fairly straightforward: the more nights you spend at participating hotels, the faster you'll earn a free night.
As seen in the EXECUTING phase, the map will write (using Mapper.Context.write()) its output into a circular in-memory buffer (MapTask.MapOutputBuffer). The size of this buffer is fixed and determined by the configuration parameter mapreduce.task.io.sort.mb (default: 100MB).
The MapReduce framework is inspired by the Map and Reduce functions used in functional programming. Computational processing occurs on data stored in a file system or within a database, which takes a set of input key values and produces a set of output key values.