Java Metrics示例代码

Question

I am newbie to metrics and I don't understand why I am getting this output Please somebody explain. Thanks in advance.

package sample;
  import com.codahale.metrics.*;
  import java.util.concurrent.TimeUnit;

  public class GetStarted {
    static final MetricRegistry metrics = new MetricRegistry();
    public static void main(String args[]) {
      startReport();
      Meter requests = metrics.meter("requests");
      requests.mark();
      wait5Seconds();
    }

  static void startReport() {
      ConsoleReporter reporter = ConsoleReporter.forRegistry(metrics)
          .convertRatesTo(TimeUnit.SECONDS)
          .convertDurationsTo(TimeUnit.MILLISECONDS)
          .build();
      reporter.start(1, TimeUnit.SECONDS);
  }

  static void wait5Seconds() {
      try {
          Thread.sleep(5*1000);
      }
      catch(InterruptedException e) {}
  }
}

Output :

12/18/15 12:01:15 PM ===========================================================

-- Meters ---------------------------------------------------------------------- requests count = 1 mean rate = 1.00 events/second 1-minute rate = 0.00 events/second 5-minute rate = 0.00 events/second 15-minute rate = 0.00 events/second

12/18/15 12:01:16 PM ===========================================================

-- Meters ---------------------------------------------------------------------- requests count = 1 mean rate = 0.50 events/second 1-minute rate = 0.00 events/second 5-minute rate = 0.00 events/second 15-minute rate = 0.00 events/second

12/18/15 12:01:17 PM ===========================================================

-- Meters ---------------------------------------------------------------------- requests count = 1 mean rate = 0.33 events/second 1-minute rate = 0.00 events/second 5-minute rate = 0.00 events/second 15-minute rate = 0.00 events/second

12/18/15 12:01:18 PM ===========================================================

-- Meters ---------------------------------------------------------------------- requests count = 1 mean rate = 0.25 events/second 1-minute rate = 0.00 events/second 5-minute rate = 0.00 events/second 15-minute rate = 0.00 events/second

12/18/15 12:01:19 PM ===========================================================

-- Meters ---------------------------------------------------------------------- requests count = 1 mean rate = 0.20 events/second 1-minute rate = 0.00 events/second 5-minute rate = 0.00 events/second 15-minute rate = 0.00 events/second

Answer 1

After creating registry, you have started the reporter with 1 second interval. So for each second, your console reporter will output to console.

You have chosen meter type metric which will give you count(no of times this event occurred) and mean rate (average rate). Other rates will be zero because a single time unit of that measurement is not yet over. Eg. You ran the program only for 5 seconds so you will not get 1 minute rate. Let it run for more than 1 minute you can see other rates with some value.

requests.mark();

The above line is used to mark the occurrence of an event. As you have invoked it once a metric event will be triggered. As you are not calling this method any more in the program, so count remains 1.

mean rate is (total count from start of application)/(total time in secs from start). Note: here it is seconds. For every second reporter is printing. As count=1, at 1st sec rate= (1 count)/(1sec). at 2nd sec rate = (1 count)/(2 sec)=0.5 , at 3rd sec rate = (1 count)/(3 sec) = 0.33

1 min rate is (total count in last 1 min)/(60 secs). 1 min rates here it is zero because still 1 minute has not passed. Same for the following big interval rates

5 min rate is (total count in last 5 min)/(5*60 secs) . 5 mins = 5*60 secs

You might expect the thread to sleep and thereby expecting a gap of 5 secs in the log. But the reporter is running in a different thread. So here sleeping for 5 secs is of no value except make the program run to 5 seconds.