metrics: Refactor handling of histogram vectors (#18632)

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))
+	}
+}