zio.metrics

A Metric[In, Out] represents a concurrent metric, which accepts updates of type In, which are aggregated to a stateful value of type Out.

For example, a counter metric would have type Metric[Double, Double], representing the fact that the metric can be updated with doubles (the amount to increment or decrement the counter by), and the state of the counter is a double.

There are five primitive metric types supported by ZIO:

• Counters
• Frequencies
• Gauges
• Histograms
• Summaries

The companion object contains constructors for these primitive metrics. All metrics are derived from these primitive metrics.

A MetricKey is a unique key associated with each metric. The key is based on a combination of the metric type, the name and tags associated with the metric, and any other information to describe a a metric, such as the boundaries of a histogram. In this way, it is impossible to ever create different metrics with conflicting keys.

A MetricLabel represents a key value pair that allows analyzing metrics at an additional level of granularity. For example if a metric tracks the response time of a service labels could be used to create separate versions that track response times for different clients.

A MetricState describes the state of a metric. The type parameter of a metric state corresponds to the type of the metric key (MetricKeyType). This phantom type parameter is used to tie keys to their expected states.

A PollingMetric[Type, Out] is a combination of a metric and an effect that polls for updates to the metric.