Libraries monitor your application

We saw what the JVM provides us with tools and what the server gives us performance hints, but there are a lot of libraries intended to help you work on the performance.

Counters, gauges, timers, and more

The most famous library is probably Metrics from Dropwizard (http://metrics.dropwizard.io) but all libraries share more or less the same sort of API. The metrics are centered around a few important concepts:

• Gauges: These provide the measure of a value at a certain time. They are intended to build a time series. Most famous examples are the CPU or memory usages.
• Counters: These are long values, often associated with a gauges in order to build time series.
• Histogram: This structure allows...