Dropwizard IO Metrics are always aggregated - aggregate

Question

I'm trying to monitor some metrics via Dropwizard IO Metrics. I want to get number of files downloaded in a specific time period, and I want to aggregate that metric by myself. So for example, let's say between 10.00 to 10.15, 60 files are downloaded. I want the metric to be 60 between this period and after 10.15, it must return zero. However, after 10.15, the metric always returns 60. Is there a way to avoid its automatic aggregation?

Answer 1

This is possible, you are just using the wrong metric I assume. You will have to use a metric that uses time windows and configure them correctly. Look at this simple example I wrote up:
public class MetricTest {
public static final long SLEEP_TIME = 51;
public static void main(String[] args) throws InterruptedException {
SlidingTimeWindowReservoir reservoir = new SlidingTimeWindowReservoir(50, TimeUnit.MILLISECONDS);
Histogram h = new Histogram(reservoir);
h.update(1);
System.out.println(h.getSnapshot().size());
Thread.sleep(SLEEP_TIME);
h.update(1);
System.out.println(h.getSnapshot().size());
Thread.sleep(SLEEP_TIME);
h.update(1);
System.out.println(h.getSnapshot().size());
Thread.sleep(SLEEP_TIME);
h.update(1);
System.out.println(h.getSnapshot().size());
Thread.sleep(SLEEP_TIME);
h.update(1);
System.out.println(h.getSnapshot().size());
Thread.sleep(SLEEP_TIME);
h.update(1);
System.out.println(h.getSnapshot().size());
}
}
I am using a histogram to count the amount of values I submitted. See the SLEEP_TIME constant above for expiry.
If I run this with a sleep time of 0, i get:
1 2 3 4 5 6
If I run it with a sleep time of 51, the previous value is expired each time a snapshot is created, and I get:
1 1 1 1 1 1
You can write your own window implementation that simply does bucketing and deletes old buckets.
I hope that clarifies how metrics work.
Artur