job.setNumReduceTasks(0);
job.setOutputKeyClass(NullWritable.class);
job.setOutputValueClass(NullWritable.class);
job.setOutputFormatClass(NullOutputFormat.class);
scanTimer.start();
job.waitForCompletion(true);
scanTimer.stop();
Counters counters = job.getCounters();
long numRows = counters.findCounter(ScanCounter.NUM_ROWS).getValue();