metrics.go

package baker

import (
	"fmt"
	"time"
)

// A MetricsBag is collection of metrics, those metrics are reported by
// every Baker components, through their Stats method.
// Stats() is called once per second, and contains a MetricsBag filled
// with values relative to that last second.
type MetricsBag map[string]interface{}

// AddRawCounter adds a metric of type counter to the bag and sets its current value.
// A counter is a cumulative metric that can only increase.
// To be meaningful, value must be positive.
func (bag MetricsBag) AddRawCounter(name string, value int64) {
	bag["c:"+name] = value
}

// AddDeltaCounter adds a metric of type counter to the bag and increments its value.
// A counter is a cumulative metric that can only increase.
// To be meaningful, delta must be positive.
func (bag MetricsBag) AddDeltaCounter(name string, delta int64) {
	bag["d:"+name] = delta
}

// AddGauge adds a metric of type gauge to the bag and updates its value.
// A gauge represents a single numerical data point that can arbitrarily go up and down.
func (bag MetricsBag) AddGauge(name string, value float64) {
	bag["g:"+name] = value
}

// AddHistogram adds a metrics of type histogram to the bag and tracks its value.
// A histogram samples observations and counts them in different 'buckets' in order
// to track and show the statistical distribution of a set of values.
func (bag MetricsBag) AddHistogram(name string, values []float64) {
	bag["h:"+name] = values
}

// AddTimings adds a metric of type histogram to the bag and tracks its value.
// Timing is basically a histogram but allows to sample values of type time.Duration.
// A histogram samples observations and counts them in different 'buckets'.
func (bag MetricsBag) AddTimings(name string, values []time.Duration) {
	bag["t:"+name] = values
}

// Merge merges metrics with the same name and types from another MetricsBag into this bag.
// Counters are summed up, gauges are averaged, and histograms are concatenated.
func (bag MetricsBag) Merge(other MetricsBag) {
	for key, val := range other {
		switch key[0] {
		case 'c', 'd':
			// Counters and deltas should be summed
			if _, ok := bag[key]; !ok {
				bag[key] = int64(0)
			}
			bag[key] = bag[key].(int64) + val.(int64)
		case 'g':
			// Gauges must be averaged
			if _, ok := bag[key]; !ok {
				bag[key] = val.(float64)
			}
			bag[key] = (bag[key].(float64) + val.(float64)) / 2

		case 'h':
			// Histograms are concatenated
			if _, ok := bag[key]; !ok {
				bag[key] = []float64{}
			}
			bag[key] = append(bag[key].([]float64), val.([]float64)...)

		case 't':
			// timings are concatenated
			if _, ok := bag[key]; !ok {
				bag[key] = []time.Duration{}
			}
			bag[key] = append(bag[key].([]time.Duration), val.([]time.Duration)...)

		default:
			panic(fmt.Errorf("unsupported key %q", key))
		}
	}
}