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 you to compute the statistics around a value, for instance, the mean or the percentiles of request lengths.
- Timers: These are a bit like histograms; they compute other metrics based on one metric. Here, the goal is to have ...
