可以在Map器中设置计数器。
从Map器发出单词时，递增全局计数器以计算单词总数。
在减速机中使用计数器来获得发出的单词总数。
使用一般方法计算百分比。

job.setJarByClass(WinnerCount.class);
    job.setMapperClass(WinnerCountMapper.class);
    //job.setCombinerClass(WinnerCountCombiner.class);
    job.setCombinerClass(WinnerCountCombiner.class);
    job.setReducerClass(WinnerCountReducer.class);
    job.setInputFormatClass(ChessInputFormat.class);
    job.setOutputKeyClass(Text.class);
    job.setOutputValueClass(IntWritable.class);
    FileInputFormat.addInputPath(job, new Path(inputPath));
    FileOutputFormat.setOutputPath(job, temp);

    job.waitForCompletion(true);

    Counters counters = job.getCounters();
    Counter total = counters.findCounter(WinnerCountMapper.MAP_COUNTER.TOTAL_TUPLE);
    //System.out.println(total.getDisplayName()+":"+total.getValue());

    /*if (hdfs.exists(output))
        hdfs.delete(output, true);*/

    Configuration conf2 = new Configuration();
    conf2.set("total", total.getValue()+"");
    Job job2 = Job.getInstance(conf2,"aggregation");

    job2.setJarByClass(WinnerCount.class);
    job2.setMapperClass(AggregationMapper.class);
    job2.setReducerClass(AggregationReducer.class);
    job2.setOutputKeyClass(Text.class);
    job2.setOutputValueClass(Text.class);