Map refers to the process of chopping input into a smaller set of sub-problems for processing (where these sub-problems are distributed to parallel workers).
映射是指把大量输入处理成更小的子问题集(然后把这些子问题分发给并行的工作系统)。
2
Not only are mapping and reduction amenable to parallelization, but the map and reduce operations can be combined into a single parallel pass, which is even more efficient.
不仅映射和减法支持并行化，映射和减法运算也可结合到单个并行循环中，这样效率更高。
3
MapReduce breaks down a problem into millions of parallel computations in the Map phase, producing as its output a stream of key-value pairs.