bench(ruler): add benchmark for select merging query reduction

Author: alanprot

pkg/ruler/select_merger_bench_test.go

@@ -0,0 +1,98 @@
+package ruler
+
+import (
+	"context"
+	"fmt"
+	"sync/atomic"
+	"testing"
+	"time"
+
+	"github.com/prometheus/prometheus/model/labels"
+	"github.com/prometheus/prometheus/promql"
+	"github.com/prometheus/prometheus/promql/parser"
+	"github.com/prometheus/prometheus/rules"
+)
+
+// BenchmarkSelectMerger simulates 114 rules (38 metrics × 3 deploy_color variants)
+// and compares query count with vs without merging.
+func BenchmarkSelectMerger(b *testing.B) {
+	const (
+		numMetrics = 38
+		numColors  = 3
+		seriesPer  = 50
+	)
+	colors := []string{"blue", "green", "canary"}
+
+	// Build 114 rules: 38 metrics × 3 deploy_color variants.
+	rls := make([]rules.Rule, 0, numMetrics*numColors)
+	for i := range numMetrics {
+		for _, c := range colors {
+			expr := fmt.Sprintf(`sum(metric_%d{deploy_color="%s",job="svc"})`, i, c)
+			e, err := parser.ParseExpr(expr)
+			if err != nil {
+				b.Fatal(err)
+			}
+			rls = append(rls, &fakeRule{expr: e})
+		}
+	}
+
+	// Mock QueryFunc: returns seriesPer samples with varying deploy_color.
+	mockQueryFunc := func(_ context.Context, qs string, _ time.Time) (promql.Vector, error) {
+		vec := make(promql.Vector, seriesPer)
+		for i := range vec {
+			vec[i] = promql.Sample{
+				Metric: labels.FromStrings(
+					"__name__", "metric_0",
+					"deploy_color", colors[i%numColors],
+					"job", "svc",
+					"instance", fmt.Sprintf("host-%d", i),
+				),
+				T: 0,
+				F: float64(i),
+			}
+		}
+		return vec, nil
+	}
+
+	ts := time.Now()
+	ctx := context.Background()
+
+	b.Run("without_merging", func(b *testing.B) {
+		var calls atomic.Int64
+		qf := func(ctx context.Context, qs string, t time.Time) (promql.Vector, error) {
+			calls.Add(1)
+			return mockQueryFunc(ctx, qs, t)
+		}
+		for b.Loop() {
+			calls.Store(0)
+			for _, r := range rls {
+				_, err := qf(ctx, r.Query().String(), ts)
+				if err != nil {
+					b.Fatal(err)
+				}
+			}
+		}
+		b.ReportMetric(float64(calls.Load()), "queries/op")
+	})
+
+	b.Run("with_merging", func(b *testing.B) {
+		plan := planMergedSelects(rls, 2)
+		var calls atomic.Int64
+		qf := func(ctx context.Context, qs string, t time.Time) (promql.Vector, error) {
+			calls.Add(1)
+			return mockQueryFunc(ctx, qs, t)
+		}
+		for b.Loop() {
+			calls.Store(0)
+			cache := executePrefetch(ctx, plan, qf, ts)
+			cached := cachedQueryFunc(qf, cache)
+			for _, r := range rls {
+				_, err := cached(ctx, r.Query().String(), ts)
+				if err != nil {
+					b.Fatal(err)
+				}
+			}
+		}
+		b.ReportMetric(float64(calls.Load()), "queries/op")
+	})
+}