您可以实现自定义哈希分区器，这样您就可以将频率更高的键发送到一个reducer，并将频率更低的所有其他键发送到其他reducer。

public static class AgePartitioner extends Partitioner<Text, Text> {

        @Override
        public int getPartition(Text key, Text value, int numReduceTasks) {

            //we have more keys in this range so we want to sent them to one reducer
            if(key >20 && key <=30){

                return 1 ;
            }
           else
                return 0;

        }
    }