etcdserver: use Histogram for proposal_durations

etcdserver/metrics.go

@@ -23,11 +23,12 @@ import (
 
 var (
 	// TODO: with label in v3?
-	proposeDurations = prometheus.NewSummary(prometheus.SummaryOpts{
+	proposeDurations = prometheus.NewHistogram(prometheus.HistogramOpts{
 		Namespace: "etcd",
 		Subsystem: "server",
-		Name:      "proposal_durations_milliseconds",
+		Name:      "proposal_durations_seconds",
 		Help:      "The latency distributions of committing proposal.",
+		Buckets:   prometheus.ExponentialBuckets(0.001, 2, 14),
 	})
 	proposePending = prometheus.NewGauge(prometheus.GaugeOpts{
 		Namespace: "etcd",

etcdserver/server.go

@@ -598,7 +598,7 @@ func (s *EtcdServer) Do(ctx context.Context, r pb.Request) (Response, error) {
 
 		select {
 		case x := <-ch:
-			proposeDurations.Observe(float64(time.Since(start).Nanoseconds() / int64(time.Millisecond)))
+			proposeDurations.Observe(float64(time.Since(start)) / float64(time.Second))
 			resp := x.(Response)
 			return resp, resp.err
 		case <-ctx.Done():