add prometheus support for stats.NewHistogram

Signed-off-by: Michael Demmer <mdemmer@slack-corp.com>

go/stats/histogram.go

@@ -27,6 +27,8 @@ import (
 // splitting the counts under different buckets
 // using specified cutoffs.
 type Histogram struct {
+	help       string
+	labelName  string
 	cutoffs    []int64
 	labels     []string
 	countLabel string
@@ -41,24 +43,25 @@ type Histogram struct {
 // based on the cutoffs. The buckets are categorized using the
 // following criterion: cutoff[i-1] < value <= cutoff[i]. Anything
 // higher than the highest cutoff is labeled as "inf".
-func NewHistogram(name string, cutoffs []int64) *Histogram {
+func NewHistogram(name, help string, cutoffs []int64) *Histogram {
 	labels := make([]string, len(cutoffs)+1)
 	for i, v := range cutoffs {
 		labels[i] = fmt.Sprintf("%d", v)
 	}
 	labels[len(labels)-1] = "inf"
-	return NewGenericHistogram(name, cutoffs, labels, "Count", "Total")
+	return NewGenericHistogram(name, help, cutoffs, labels, "Count", "Total")
 }
 
 // NewGenericHistogram creates a histogram where all the labels are
 // supplied by the caller. The number of labels has to be one more than
 // the number of cutoffs because the last label captures everything that
 // exceeds the highest cutoff.
-func NewGenericHistogram(name string, cutoffs []int64, labels []string, countLabel, totalLabel string) *Histogram {
+func NewGenericHistogram(name, help string, cutoffs []int64, labels []string, countLabel, totalLabel string) *Histogram {
 	if len(cutoffs) != len(labels)-1 {
 		panic("mismatched cutoff and label lengths")
 	}
 	h := &Histogram{
+		help:       help,
 		cutoffs:    cutoffs,
 		labels:     labels,
 		countLabel: countLabel,
@@ -160,3 +163,13 @@ func (h *Histogram) Buckets() []int64 {
 	}
 	return buckets
 }
+
+// Help returns the help string.
+func (h *Histogram) Help() string {
+	return h.help
+}
+
+// LabelName returns the label name.
+func (h *Histogram) LabelName() string {
+	return h.labelName
+}

go/stats/histogram_test.go

@@ -23,7 +23,7 @@ import (
 
 func TestHistogram(t *testing.T) {
 	clear()
-	h := NewHistogram("hist1", []int64{1, 5})
+	h := NewHistogram("hist1", "desc1", []int64{1, 5})
 	for i := 0; i < 10; i++ {
 		h.Add(int64(i))
 	}
@@ -57,6 +57,7 @@ func TestGenericHistogram(t *testing.T) {
 	clear()
 	h := NewGenericHistogram(
 		"histgen",
+		"generic histogram",
 		[]int64{1, 5},
 		[]string{"one", "five", "max"},
 		"count",
@@ -78,7 +79,7 @@ func TestHistogramHook(t *testing.T) {
 	})
 
 	name := "hist2"
-	v := NewHistogram(name, []int64{1})
+	v := NewHistogram(name, "", []int64{1})
 	if gotname != name {
 		t.Errorf("got %v; want %v", gotname, name)
 	}

go/stats/prometheusbackend/collectors.go

@@ -129,8 +129,9 @@ func (c *metricsFuncWithMultiLabelsCollector) Collect(ch chan<- prometheus.Metri
 }
 
 type timingsCollector struct {
-	t    *stats.Timings
-	desc *prometheus.Desc
+	t       *stats.Timings
+	cutoffs []float64
+	desc    *prometheus.Desc
 }
 
 // Describe implements Collector.
@@ -145,16 +146,15 @@ func (c *timingsCollector) Collect(ch chan<- prometheus.Metric) {
 			c.desc,
 			uint64(his.Count()),
 			float64(his.Total()),
-			makePromBucket(his.Cutoffs(), his.Buckets()),
+			makeCumulativeBuckets(c.cutoffs, his.Buckets()),
 			cat)
 	}
 }
 
-func makePromBucket(cutoffs []int64, buckets []int64) map[float64]uint64 {
+func makeCumulativeBuckets(cutoffs []float64, buckets []int64) map[float64]uint64 {
 	output := make(map[float64]uint64)
 	last := uint64(0)
-	for i := range cutoffs {
-		key := float64(cutoffs[i]) / 1000000000
+	for i, key := range cutoffs {
 		//TODO(zmagg): int64 => uint64 conversion. error if it overflows?
 		output[key] = uint64(buckets[i]) + last
 		last = output[key]
@@ -163,8 +163,9 @@ func makePromBucket(cutoffs []int64, buckets []int64) map[float64]uint64 {
 }
 
 type multiTimingsCollector struct {
-	mt   *stats.MultiTimings
-	desc *prometheus.Desc
+	mt      *stats.MultiTimings
+	cutoffs []float64
+	desc    *prometheus.Desc
 }
 
 // Describe implements Collector.
@@ -180,7 +181,46 @@ func (c *multiTimingsCollector) Collect(ch chan<- prometheus.Metric) {
 			c.desc,
 			uint64(his.Count()),
 			float64(his.Total()),
-			makePromBucket(his.Cutoffs(), his.Buckets()),
+			makeCumulativeBuckets(c.cutoffs, his.Buckets()),
 			labelValues...)
 	}
 }
+
+type histogramCollector struct {
+	h       *stats.Histogram
+	cutoffs []float64
+	desc    *prometheus.Desc
+}
+
+func newHistogramCollector(h *stats.Histogram, name string) {
+	collector := &histogramCollector{
+		h:       h,
+		cutoffs: make([]float64, len(h.Cutoffs())),
+		desc: prometheus.NewDesc(
+			name,
+			h.Help(),
+			[]string{},
+			nil),
+	}
+
+	for i, val := range h.Cutoffs() {
+		collector.cutoffs[i] = float64(val)
+	}
+
+	prometheus.MustRegister(collector)
+}
+
+// Describe implements Collector.
+func (c *histogramCollector) Describe(ch chan<- *prometheus.Desc) {
+	ch <- c.desc
+}
+
+// Collect implements Collector.
+func (c *histogramCollector) Collect(ch chan<- prometheus.Metric) {
+	ch <- prometheus.MustNewConstHistogram(
+		c.desc,
+		uint64(c.h.Count()),
+		float64(c.h.Total()),
+		makeCumulativeBuckets(c.cutoffs, c.h.Buckets()),
+	)
+}

go/stats/prometheusbackend/prometheusbackend.go

@@ -65,6 +65,8 @@ func (be *PromBackend) publishPrometheusMetric(name string, v expvar.Var) {
 		be.newTiming(st, name)
 	case *stats.MultiTimings:
 		be.newMultiTiming(st, name)
+	case *stats.Histogram:
+		newHistogramCollector(st, be.buildPromName(name))
 	default:
 		logUnsupported.Infof("Not exporting to Prometheus an unsupported metric type of %T: %s", st, name)
 	}
@@ -138,7 +140,8 @@ func (be *PromBackend) newMetricsFuncWithMultiLabels(cfml *stats.CountersFuncWit
 
 func (be *PromBackend) newTiming(t *stats.Timings, name string) {
 	collector := &timingsCollector{
-		t: t,
+		t:       t,
+		cutoffs: make([]float64, len(t.Cutoffs())),
 		desc: prometheus.NewDesc(
 			be.buildPromName(name),
 			t.Help(),
@@ -146,12 +149,17 @@ func (be *PromBackend) newTiming(t *stats.Timings, name string) {
 			nil),
 	}
 
+	for i, val := range t.Cutoffs() {
+		collector.cutoffs[i] = float64(val) / 1000000000
+	}
+
 	prometheus.MustRegister(collector)
 }
 
 func (be *PromBackend) newMultiTiming(mt *stats.MultiTimings, name string) {
 	collector := &multiTimingsCollector{
-		mt: mt,
+		mt:      mt,
+		cutoffs: make([]float64, len(mt.Cutoffs())),
 		desc: prometheus.NewDesc(
 			be.buildPromName(name),
 			mt.Help(),
@@ -159,6 +167,10 @@ func (be *PromBackend) newMultiTiming(mt *stats.MultiTimings, name string) {
 			nil),
 	}
 
+	for i, val := range mt.Cutoffs() {
+		collector.cutoffs[i] = float64(val) / 1000000000
+	}
+
 	prometheus.MustRegister(collector)
 }
 

go/stats/prometheusbackend/prometheusbackend_test.go

@@ -290,6 +290,29 @@ func TestPrometheusMultiTimings_PanicWrongLength(t *testing.T) {
 	c.Add([]string{"label1"}, time.Duration(100000000))
 }
 
+func TestPrometheusHistogram(t *testing.T) {
+	name := "blah_hist"
+	hist := stats.NewHistogram(name, "help", []int64{1, 5, 10})
+	hist.Add(2)
+	hist.Add(3)
+	hist.Add(6)
+
+	response := testMetricsHandler(t)
+	var s []string
+
+	s = append(s, fmt.Sprintf("%s_%s_bucket{le=\"1\"} %d", namespace, name, 0))
+	s = append(s, fmt.Sprintf("%s_%s_bucket{le=\"5\"} %d", namespace, name, 2))
+	s = append(s, fmt.Sprintf("%s_%s_bucket{le=\"10\"} %d", namespace, name, 3))
+	s = append(s, fmt.Sprintf("%s_%s_sum %d", namespace, name, 1))
+	s = append(s, fmt.Sprintf("%s_%s_count %d", namespace, name, 3))
+
+	for _, line := range s {
+		if !strings.Contains(response.Body.String(), line) {
+			t.Fatalf("Expected result to contain %s, got %s", line, response.Body.String())
+		}
+	}
+}
+
 func testMetricsHandler(t *testing.T) *httptest.ResponseRecorder {
 	req, _ := http.NewRequest("GET", "/metrics", nil)
 	response := httptest.NewRecorder()

go/stats/timings.go

@@ -52,7 +52,7 @@ func NewTimings(name, help, labelName string, categories ...string) *Timings {
 		labelName:  labelName,
 	}
 	for _, cat := range categories {
-		t.histograms[cat] = NewGenericHistogram("", bucketCutoffs, bucketLabels, "Count", "Time")
+		t.histograms[cat] = NewGenericHistogram("", "", bucketCutoffs, bucketLabels, "Count", "Time")
 	}
 	if name != "" {
 		publish(name, t)
@@ -74,7 +74,7 @@ func (t *Timings) Add(name string, elapsed time.Duration) {
 		t.mu.Lock()
 		hist, ok = t.histograms[name]
 		if !ok {
-			hist = NewGenericHistogram("", bucketCutoffs, bucketLabels, "Count", "Time")
+			hist = NewGenericHistogram("", "", bucketCutoffs, bucketLabels, "Count", "Time")
 			t.histograms[name] = hist
 		}
 		t.mu.Unlock()

go/vt/vttablet/tabletserver/tabletenv/tabletenv.go

@@ -93,7 +93,9 @@ var (
 		"Total transaction latency for each CallerID",
 		[]string{"CallerID", "Conclusion"})
 	// ResultStats shows the histogram of number of rows returned.
-	ResultStats = stats.NewHistogram("Results", []int64{0, 1, 5, 10, 50, 100, 500, 1000, 5000, 10000})
+	ResultStats = stats.NewHistogram("Results",
+		"Distribution of rows returned",
+		[]int64{0, 1, 5, 10, 50, 100, 500, 1000, 5000, 10000})
 	// TableaclAllowed tracks the number allows.
 	TableaclAllowed = stats.NewCountersWithMultiLabels(
 		"TableACLAllowed",