metrics: expvar support for ResettingTimer (#16878)

* metrics: expvar support for ResettingTimer

* metrics: use integers for percentiles; remove Overall

* metrics: fix edge-case panic for index-out-of-range

3 files changed, 124 insertions, 1 deletions

diff --git a/metrics/exp/exp.go b/metrics/exp/exp.go
index c19d00a94..625ffd4e8 100644
--- a/metrics/exp/exp.go
+++ b/metrics/exp/exp.go
@@ -134,6 +134,17 @@ func (exp *exp) publishTimer(name string, metric metrics.Timer) {
 	exp.getFloat(name + ".mean-rate").Set(t.RateMean())
 }
 
+func (exp *exp) publishResettingTimer(name string, metric metrics.ResettingTimer) {
+	t := metric.Snapshot()
+	ps := t.Percentiles([]float64{50, 75, 95, 99})
+	exp.getInt(name + ".count").Set(int64(len(t.Values())))
+	exp.getFloat(name + ".mean").Set(t.Mean())
+	exp.getInt(name + ".50-percentile").Set(ps[0])
+	exp.getInt(name + ".75-percentile").Set(ps[1])
+	exp.getInt(name + ".95-percentile").Set(ps[2])
+	exp.getInt(name + ".99-percentile").Set(ps[3])
+}
+
 func (exp *exp) syncToExpvar() {
 	exp.registry.Each(func(name string, i interface{}) {
 		switch i.(type) {
@@ -149,6 +160,8 @@ func (exp *exp) syncToExpvar() {
 			exp.publishMeter(name, i.(metrics.Meter))
 		case metrics.Timer:
 			exp.publishTimer(name, i.(metrics.Timer))
+		case metrics.ResettingTimer:
+			exp.publishResettingTimer(name, i.(metrics.ResettingTimer))
 		default:
 			panic(fmt.Sprintf("unsupported type for '%s': %T", name, i))
 		}
diff --git a/metrics/resetting_timer.go b/metrics/resetting_timer.go
index 57bcb3134..f33a9f8aa 100644
--- a/metrics/resetting_timer.go
+++ b/metrics/resetting_timer.go
@@ -210,7 +210,7 @@ func (t *ResettingTimerSnapshot) calc(percentiles []float64) {
 				// poor man's math.Round(x):
 				// math.Floor(x + 0.5)
 				indexOfPerc := int(math.Floor(((abs / 100.0) * float64(count)) + 0.5))
-				if pct >= 0 {
+				if pct >= 0 && indexOfPerc > 0 {
 					indexOfPerc -= 1 // index offset=0
 				}
 				thresholdBoundary = t.values[indexOfPerc]
diff --git a/metrics/resetting_timer_test.go b/metrics/resetting_timer_test.go
index 58fd47f35..77c49dc38 100644
--- a/metrics/resetting_timer_test.go
+++ b/metrics/resetting_timer_test.go
@@ -104,3 +104,113 @@ func TestResettingTimer(t *testing.T) {
 		}
 	}
 }
+
+func TestResettingTimerWithFivePercentiles(t *testing.T) {
+	tests := []struct {
+		values   []int64
+		start    int
+		end      int
+		wantP05  int64
+		wantP20  int64
+		wantP50  int64
+		wantP95  int64
+		wantP99  int64
+		wantMean float64
+		wantMin  int64
+		wantMax  int64
+	}{
+		{
+			values:  []int64{},
+			start:   1,
+			end:     11,
+			wantP05: 1, wantP20: 2, wantP50: 5, wantP95: 10, wantP99: 10,
+			wantMin: 1, wantMax: 10, wantMean: 5.5,
+		},
+		{
+			values:  []int64{},
+			start:   1,
+			end:     101,
+			wantP05: 5, wantP20: 20, wantP50: 50, wantP95: 95, wantP99: 99,
+			wantMin: 1, wantMax: 100, wantMean: 50.5,
+		},
+		{
+			values:  []int64{1},
+			start:   0,
+			end:     0,
+			wantP05: 1, wantP20: 1, wantP50: 1, wantP95: 1, wantP99: 1,
+			wantMin: 1, wantMax: 1, wantMean: 1,
+		},
+		{
+			values:  []int64{0},
+			start:   0,
+			end:     0,
+			wantP05: 0, wantP20: 0, wantP50: 0, wantP95: 0, wantP99: 0,
+			wantMin: 0, wantMax: 0, wantMean: 0,
+		},
+		{
+			values:  []int64{},
+			start:   0,
+			end:     0,
+			wantP05: 0, wantP20: 0, wantP50: 0, wantP95: 0, wantP99: 0,
+			wantMin: 0, wantMax: 0, wantMean: 0,
+		},
+		{
+			values:  []int64{1, 10},
+			start:   0,
+			end:     0,
+			wantP05: 1, wantP20: 1, wantP50: 1, wantP95: 10, wantP99: 10,
+			wantMin: 1, wantMax: 10, wantMean: 5.5,
+		},
+	}
+	for ind, tt := range tests {
+		timer := NewResettingTimer()
+
+		for i := tt.start; i < tt.end; i++ {
+			tt.values = append(tt.values, int64(i))
+		}
+
+		for _, v := range tt.values {
+			timer.Update(time.Duration(v))
+		}
+
+		snap := timer.Snapshot()
+
+		ps := snap.Percentiles([]float64{5, 20, 50, 95, 99})
+
+		val := snap.Values()
+
+		if len(val) > 0 {
+			if tt.wantMin != val[0] {
+				t.Fatalf("%d: min: got %d, want %d", ind, val[0], tt.wantMin)
+			}
+
+			if tt.wantMax != val[len(val)-1] {
+				t.Fatalf("%d: max: got %d, want %d", ind, val[len(val)-1], tt.wantMax)
+			}
+		}
+
+		if tt.wantMean != snap.Mean() {
+			t.Fatalf("%d: mean: got %.2f, want %.2f", ind, snap.Mean(), tt.wantMean)
+		}
+
+		if tt.wantP05 != ps[0] {
+			t.Fatalf("%d: p05: got %d, want %d", ind, ps[0], tt.wantP05)
+		}
+
+		if tt.wantP20 != ps[1] {
+			t.Fatalf("%d: p20: got %d, want %d", ind, ps[1], tt.wantP20)
+		}
+
+		if tt.wantP50 != ps[2] {
+			t.Fatalf("%d: p50: got %d, want %d", ind, ps[2], tt.wantP50)
+		}
+
+		if tt.wantP95 != ps[3] {
+			t.Fatalf("%d: p95: got %d, want %d", ind, ps[3], tt.wantP95)
+		}
+
+		if tt.wantP99 != ps[4] {
+			t.Fatalf("%d: p99: got %d, want %d", ind, ps[4], tt.wantP99)
+		}
+	}
+}