add a test for interning in the metadata store

pstoremem/metadata_test.go

@@ -0,0 +1,59 @@
+package pstoremem
+
+import (
+	"math/rand"
+	"runtime"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/libp2p/go-libp2p-core/peer"
+)
+
+func randomString(n int) string {
+	const letters = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
+	b := make([]byte, n)
+	for i := range b {
+		b[i] = letters[rand.Intn(len(letters))]
+	}
+	return string(b)
+}
+
+func getAllocs(t *testing.T, num int, key string, value func() string) int64 {
+	getAlloc := func() uint64 {
+		runtime.GC()
+		var stats runtime.MemStats
+		runtime.ReadMemStats(&stats)
+		return stats.TotalAlloc
+	}
+
+	m := NewPeerMetadata()
+	start := getAlloc()
+	for i := 0; i < num; i++ {
+		m.Put(peer.ID(randomString(10)), key, value())
+	}
+	return int64(getAlloc()) - int64(start)
+}
+
+func TestInterning(t *testing.T) {
+	const num = 10000
+
+	t.Run("using the AgentVersion key", func(t *testing.T) {
+		const value = "agent version 1234"
+		allocsConstValue := getAllocs(t, num, "AgentVersion", func() string { return value })
+		allocsRandomValue := getAllocs(t, num, "AgentVersion", func() string { return randomString(len(value)) })
+		fraction := float64(allocsConstValue) / float64(allocsRandomValue)
+		t.Logf("using a constant AgentVersion reduced memory usage to %f", fraction)
+		require.Greater(t, fraction, 0.5)
+		require.Less(t, fraction, 0.6)
+	})
+
+	t.Run("using a different key", func(t *testing.T) {
+		const value = "agent version 1234"
+		allocsConstValue := getAllocs(t, num, "other key", func() string { return value })
+		allocsRandomValue := getAllocs(t, num, "other key", func() string { return randomString(len(value)) })
+		fraction := float64(allocsConstValue) / float64(allocsRandomValue)
+		require.Greater(t, fraction, 0.8)
+		require.Less(t, fraction, 1.2)
+	})
+}