Histogram Prometheus-compatible BUG

[dylanoy]

code

package main

import (
	"fmt"
	"io/ioutil"
	"net/http"
	"net/http/httptest"
	"time"

	"go.uber.org/net/metrics"
)

func main() {
	// First, construct a root and add some metrics.
	root := metrics.New()

	h, err := root.Scope().Histogram(metrics.HistogramSpec{
		Spec: metrics.Spec{
			Name: "selects_latency_ms",    // required, should indicate unit
			Help: "SELECT query latency.", // required
		},
		Unit:    time.Millisecond,                      // required
		Buckets: []int64{5, 10, 25, 50, 100, 200, 500}, // required
	})
	if err != nil {
		panic(err)
	}

	h.IncBucket(5)
	h.IncBucket(501)

	// Expose the root on your HTTP server of choice.
	mux := http.NewServeMux()
	mux.Handle("/debug/net/metrics", root)
	srv := httptest.NewServer(mux)
	defer srv.Close()

	// Your metrics are now exposed via a Prometheus-compatible handler. This
	// example shows text output, but clients can also request the protocol
	// buffer binary format.
	res, err := http.Get(fmt.Sprintf("%v/debug/net/metrics", srv.URL))
	if err != nil {
		panic(err)
	}
	text, err := ioutil.ReadAll(res.Body)
	res.Body.Close()
	if err != nil {
		panic(err)
	}
	fmt.Println(string(text))

}

output

# HELP selects_latency_ms SELECT query latency.
# TYPE selects_latency_ms histogram
selects_latency_ms_bucket{host="db01",table="trips",le="5"} 2
selects_latency_ms_bucket{host="db01",table="trips",le="10"} 2
selects_latency_ms_bucket{host="db01",table="trips",le="25"} 2
selects_latency_ms_bucket{host="db01",table="trips",le="50"} 2
selects_latency_ms_bucket{host="db01",table="trips",le="100"} 2
selects_latency_ms_bucket{host="db01",table="trips",le="200"} 2
selects_latency_ms_bucket{host="db01",table="trips",le="500"} 2
selects_latency_ms_bucket{host="db01",table="trips",le="+Inf"} 2
selects_latency_ms_sum{host="db01",table="trips"} 506
selects_latency_ms_count{host="db01",table="trips"} 2

system macos
golang 1.15

[dylanoy]

BUG on file
go.uber.org/net/metrics@v1.3.0/histogram.go:162

func (h *Histogram) metric() *promproto.Metric {
	n := uint64(0)
	promBuckets := make([]*promproto.Bucket, 0, len(h.buckets)-1)
	for _, b := range h.buckets {
		n += uint64(b.Load())
		if b.upper == math.MaxInt64 {
			// Prometheus doesn't want us to export the final catch-all bucket.
			continue
		}
		upper := float64(b.upper)
		promBuckets = append(promBuckets, &promproto.Bucket{
			CumulativeCount: &n,
			UpperBound:      &upper,
		})
	}

	sum := float64(h.sum.Load())
	return &promproto.Metric{
		Label: h.tagPairs,
		Histogram: &promproto.Histogram{
			SampleCount: &n,
			SampleSum:   &sum,
			Bucket:      promBuckets,
		},
	}
}