metrics: Refactor handling of histogram vectors (#18632)

cmd/metrics-v2.go

@@ -1598,47 +1598,52 @@ func getGoMetrics() *MetricsGroup {
 	return mg
 }
 
+// getHistogramMetrics fetches histogram metrics and returns it in a []Metric
+// Note: Typically used in MetricGroup.RegisterRead
+func getHistogramMetrics(hist *prometheus.HistogramVec, desc MetricDescription) []Metric {
+	ch := make(chan prometheus.Metric)
+	go func() {
+		defer close(ch)
+		// Collects prometheus metrics from hist and sends it over ch
+		hist.Collect(ch)
+	}()
+
+	// Converts metrics received into internal []Metric type
+	var metrics []Metric
+	for promMetric := range ch {
+		dtoMetric := &dto.Metric{}
+		err := promMetric.Write(dtoMetric)
+		if err != nil {
+			// Log error and continue to receive other metric
+			// values
+			logger.LogIf(GlobalContext, err)
+			continue
+		}
+
+		h := dtoMetric.GetHistogram()
+		for _, b := range h.Bucket {
+			labels := make(map[string]string)
+			for _, lp := range dtoMetric.GetLabel() {
+				labels[*lp.Name] = *lp.Value
+			}
+			labels["le"] = fmt.Sprintf("%.3f", *b.UpperBound)
+			metric := Metric{
+				Description:    desc,
+				VariableLabels: labels,
+				Value:          float64(b.GetCumulativeCount()),
+			}
+			metrics = append(metrics, metric)
+		}
+	}
+	return metrics
+}
+
 func getBucketTTFBMetric() *MetricsGroup {
 	mg := &MetricsGroup{
 		cacheInterval: 10 * time.Second,
 	}
-	mg.RegisterRead(func(ctx context.Context) (metrics []Metric) {
-		// Read prometheus metric on this channel
-		ch := make(chan prometheus.Metric)
-		var wg sync.WaitGroup
-		wg.Add(1)
-
-		// Read prometheus histogram data and convert it to internal metric data
-		go func() {
-			defer wg.Done()
-			for promMetric := range ch {
-				dtoMetric := &dto.Metric{}
-				err := promMetric.Write(dtoMetric)
-				if err != nil {
-					logger.LogIf(GlobalContext, err)
-					return
-				}
-				h := dtoMetric.GetHistogram()
-				for _, b := range h.Bucket {
-					labels := make(map[string]string)
-					for _, lp := range dtoMetric.GetLabel() {
-						labels[*lp.Name] = *lp.Value
-					}
-					labels["le"] = fmt.Sprintf("%.3f", *b.UpperBound)
-					metric := Metric{
-						Description:    getBucketTTFBDistributionMD(),
-						VariableLabels: labels,
-						Value:          float64(b.GetCumulativeCount()),
-					}
-					metrics = append(metrics, metric)
-				}
-			}
-		}()
-
-		bucketHTTPRequestsDuration.Collect(ch)
-		close(ch)
-		wg.Wait()
-		return
+	mg.RegisterRead(func(ctx context.Context) []Metric {
+		return getHistogramMetrics(bucketHTTPRequestsDuration, getBucketObjectDistributionMD())
 	})
 	return mg
 }
@@ -1647,43 +1652,8 @@ func getS3TTFBMetric() *MetricsGroup {
 	mg := &MetricsGroup{
 		cacheInterval: 10 * time.Second,
 	}
-	mg.RegisterRead(func(ctx context.Context) (metrics []Metric) {
-		// Read prometheus metric on this channel
-		ch := make(chan prometheus.Metric)
-		var wg sync.WaitGroup
-		wg.Add(1)
-
-		// Read prometheus histogram data and convert it to internal metric data
-		go func() {
-			defer wg.Done()
-			for promMetric := range ch {
-				dtoMetric := &dto.Metric{}
-				err := promMetric.Write(dtoMetric)
-				if err != nil {
-					logger.LogIf(GlobalContext, err)
-					return
-				}
-				h := dtoMetric.GetHistogram()
-				for _, b := range h.Bucket {
-					labels := make(map[string]string)
-					for _, lp := range dtoMetric.GetLabel() {
-						labels[*lp.Name] = *lp.Value
-					}
-					labels["le"] = fmt.Sprintf("%.3f", *b.UpperBound)
-					metric := Metric{
-						Description:    getS3TTFBDistributionMD(),
-						VariableLabels: labels,
-						Value:          float64(b.GetCumulativeCount()),
-					}
-					metrics = append(metrics, metric)
-				}
-			}
-		}()
-
-		httpRequestsDuration.Collect(ch)
-		close(ch)
-		wg.Wait()
-		return
+	mg.RegisterRead(func(ctx context.Context) []Metric {
+		return getHistogramMetrics(httpRequestsDuration, getS3TTFBDistributionMD())
 	})
 	return mg
 }

cmd/metrics-v2_test.go

@@ -0,0 +1,87 @@
+// Copyright (c) 2015-2023 MinIO, Inc.
+//
+// This file is part of MinIO Object Storage stack
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package cmd
+
+import (
+	"testing"
+	"time"
+
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+func TestGetHistogramMetrics(t *testing.T) {
+	histBuckets := []float64{0.05, 0.1, 0.25, 0.5, 0.75}
+	labels := []string{"GetObject", "PutObject", "CopyObject", "CompleteMultipartUpload"}
+	ttfbHist := prometheus.NewHistogramVec(
+		prometheus.HistogramOpts{
+			Name:    "s3_ttfb_seconds",
+			Help:    "Time taken by requests served by current MinIO server instance",
+			Buckets: histBuckets,
+		},
+		[]string{"api"},
+	)
+	observations := []struct {
+		val   float64
+		label string
+	}{
+		{
+			val:   0.02,
+			label: labels[0],
+		},
+		{
+			val:   0.07,
+			label: labels[1],
+		},
+		{
+			val:   0.11,
+			label: labels[1],
+		},
+		{
+			val:   0.19,
+			label: labels[1],
+		},
+		{
+			val:   0.31,
+			label: labels[1],
+		},
+		{
+			val:   0.61,
+			label: labels[3],
+		},
+		{
+			val:   0.79,
+			label: labels[2],
+		},
+	}
+	ticker := time.NewTicker(1 * time.Millisecond)
+	defer ticker.Stop()
+	for _, obs := range observations {
+		// Send observations once every 1ms, to simulate delay between
+		// observations. This is to test the channel based
+		// synchronization used internally.
+		select {
+		case <-ticker.C:
+			ttfbHist.With(prometheus.Labels{"api": obs.label}).Observe(obs.val)
+		}
+	}
+
+	metrics := getHistogramMetrics(ttfbHist, getBucketTTFBDistributionMD())
+	if expPoints := len(labels) * len(histBuckets); expPoints != len(metrics) {
+		t.Fatalf("Expected %v data points but got %v", expPoints, len(metrics))
+	}
+}