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Input

Metrics input are the measurement instruments that are called from application code. The inputs are high-level components that are assumed to be callable from all contexts, regardless of threading, security, etc.

Each metric input has a name and a kind. A metric's name is a short alphanumeric identifier. A metric's kind can be one of four kinds:

Counter
Marker
Timer
Gauge

The actual flow of measured values varies depending on how the metrics backend has been configured. Skip to the output section for more details on backend configuration.

Counters and Markers

Timers

Gauges

namespace

Related metrics can share a namespace:

let app_metrics = metric_scope(to_stdout());
let db_metrics = app_metrics.add_prefix("database");
let _db_timer = db_metrics.timer("db_timer");
let _db_counter = db_metrics.counter("db_counter");

proxy

counter

marker

timer

Timers can be used multiple ways:

let app_metrics = metric_scope(to_stdout());
let timer =  app_metrics.timer("my_timer");
time!(timer, {/* slow code here */} );
timer.time(|| {/* slow code here */} );

let start = timer.start();
/* slow code here */
timer.stop(start);

timer.interval_us(123_456);

gauge

ad-hoc metrics

Where necessary, metrics can also be defined ad-hoc (or "inline"):

let user_name = "john_day";
let app_metrics = metric_scope(to_log()).with_cache(512);
app_metrics.gauge(format!("gauge_for_user_{}", user_name)).value(44);

ad-hoc metrics cache

Defining a cache is optional but will speed up re-definition of common ad-hoc metrics.

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