hadoop shuffle阶段重要设置

mapreduce.reduce.shuffle.input.buffer.percent：

    mapreduce.reduce.shuffle.input.buffer.percent tells about the percentage of the reducer's heap memory to be allocated for the circular buffer to store the intermediate outputs copied from multiple mappers.

mapreduce.reduce.shuffle.memory.limit.percent：

默认为0.25可以设置小一点0.1，这个和shuffle阶段fetcher的线程个数相关，线程变多了索要占用的资源就多了。