...
Histograms
Metrics that show the quantity quantities or current consumption of resources e.g. memory or disk space should use a Histogram. We will be adding support for these . To add a metric that uses Histograms, call the diagnostics.metrics.record method in node/diagnostics/package.scala soon. These will be are polled periodically and added to KamonPrometheus. Most of the current use of Gauges in node/diagnostics/JvmMetrics.scala will migrate to Histograms. See an example in comm/rp/Connect.scala.
Timers
Metrics that show how long some class of task takes to perform should use Timers. Support for them will be added in node/diagnostics/package.scala soon. Examples of the use of Timers are time to process a transaction, achieve consensus on a block, ping times, or resource latency.
...