Class Histogram

All Implemented Interfaces:
Collector.Describable

public class Histogram extends SimpleCollector<Histogram.Child> implements Collector.Describable
Histogram metric, to track distributions of events.

Example of uses for Histograms include:

  • Response latency
  • Request size

Note: Each bucket is one timeseries. Many buckets and/or many dimensions with labels can produce large amount of time series, that may cause performance problems.

The default buckets are intended to cover a typical web/rpc request from milliseconds to seconds.

Example Histograms:

 
   class YourClass {
     static final Histogram requestLatency = Histogram.build()
         .name("requests_latency_seconds").help("Request latency in seconds.").register();

     void processRequest(Request req) {
        Histogram.Timer requestTimer = requestLatency.startTimer();
        try {
          // Your code here.
        } finally {
          requestTimer.observeDuration();
        }
     }

     // Or if using Java 8 lambdas.
     void processRequestLambda(Request req) {
        requestLatency.time(() -> {
          // Your code here.
        });
     }
   }
 
 

You can choose your own buckets:

 
     static final Histogram requestLatency = Histogram.build()
         .buckets(.01, .02, .03, .04)
         .name("requests_latency_seconds").help("Request latency in seconds.").register();
 
 
linearBuckets and exponentialBuckets offer easy ways to set common bucket patterns.
  • Field Details

    • buckets

      private final double[] buckets
  • Constructor Details

  • Method Details

    • build

      public static Histogram.Builder build(String name, String help)
      Return a Builder to allow configuration of a new Histogram. Ensures required fields are provided.
      Parameters:
      name - The name of the metric
      help - The help string of the metric
    • build

      public static Histogram.Builder build()
      Return a Builder to allow configuration of a new Histogram.
    • newChild

      protected Histogram.Child newChild()
      Description copied from class: SimpleCollector
      Return a new child, workaround for Java generics limitations.
      Specified by:
      newChild in class SimpleCollector<Histogram.Child>
    • observe

      public void observe(double amt)
      Observe the given amount on the histogram with no labels.
    • startTimer

      public Histogram.Timer startTimer()
      Start a timer to track a duration on the histogram with no labels.

      Call Histogram.Timer.observeDuration() at the end of what you want to measure the duration of.

    • time

      public double time(Runnable timeable)
      Executes runnable code (e.g. a Java 8 Lambda) and observes a duration of how long it took to run.
      Parameters:
      timeable - Code that is being timed
      Returns:
      Measured duration in seconds for timeable to complete.
    • time

      public <E> E time(Callable<E> timeable)
      Executes callable code (e.g. a Java 8 Lambda) and observes a duration of how long it took to run.
      Parameters:
      timeable - Code that is being timed
      Returns:
      Result returned by callable.
    • collect

      Description copied from class: Collector
      Return all of the metrics of this Collector.
      Specified by:
      collect in class Collector
    • describe

      public List<Collector.MetricFamilySamples> describe()
      Description copied from interface: Collector.Describable
      Provide a list of metric families this Collector is expected to return. These should exclude the samples. This is used by the registry to detect collisions and duplicate registrations. Usually custom collectors do not have to implement Describable. If Describable is not implemented and the CollectorRegistry was created with auto describe enabled (which is the case for the default registry) then Collector.collect() will be called at registration time instead of describe. If this could cause problems, either implement a proper describe, or if that's not practical have describe return an empty list.
      Specified by:
      describe in interface Collector.Describable
    • getBuckets

      double[] getBuckets()