说明：  MapReduce是一个为了处理和生成大数据集而设计的编程模型以及相关的实现。在该模型中，用户定义一个处理“键/值”对(key/value pair)的映射函数(map function)用来生成一系列中间的“键/值”对，以及一个还原函数(reduce function)用来合并所有的映射到同一键(key)的值(value)。
(MapReduce is an order processing and designed to generate large data sets and the associated programming model implementation. In this model, users define a treatment " key/value" of (key/value pair) of the mapping function (map function) is used to generate a series of intermediate " key/value" pairs, and a restore function (reduce function) used to merge all the maps to the same key (key) value (value).)