diff --git a/runner/calldata.go b/runner/calldata.go
index 07b236ce..10e1181c 100644
--- a/runner/calldata.go
+++ b/runner/calldata.go
@@ -7,6 +7,7 @@ import (
 	htmlTemplate "html/template"
 	"math/rand"
 	"strings"
+	"sync"
 	"text/template"
 	"text/template/parse"
 	"time"
@@ -19,8 +20,11 @@ import (
 const charset = "abcdefghijklmnopqrstuvwxyz" +
 	"ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
 
-var seededRand *rand.Rand = rand.New(
-	rand.NewSource(time.Now().UnixNano()))
+var seededRandPool = sync.Pool{
+	New: func() interface{} {
+		return rand.New(rand.NewSource(time.Now().UnixNano()))
+	},
+}
 
 var sprigFuncMap htmlTemplate.FuncMap = sprig.FuncMap()
 
@@ -178,7 +182,10 @@ func (td *CallData) ExecuteData(data string) ([]byte, error) {
 	if len(data) > 0 {
 		input := []byte(data)
 		tpl, err := td.execute(data)
-		if err == nil && tpl != nil {
+		if err != nil {
+			return nil, err
+		}
+		if tpl != nil {
 			input = tpl.Bytes()
 		}
 
@@ -227,15 +234,21 @@ const minLen = 2
 
 func stringWithCharset(length int, charset string) string {
 	b := make([]byte, length)
+	rng := seededRandPool.Get().(*rand.Rand)
+	defer seededRandPool.Put(rng)
 	for i := range b {
-		b[i] = charset[seededRand.Intn(len(charset))]
+		b[i] = charset[rng.Intn(len(charset))]
 	}
 	return string(b)
 }
 
 func randomString(length int) string {
 	if length <= 0 {
-		length = seededRand.Intn(maxLen-minLen+1) + minLen
+		func() {
+			rng := seededRandPool.Get().(*rand.Rand)
+			defer seededRandPool.Put(rng)
+			length = rng.Intn(maxLen-minLen+1) + minLen
+		}()
 	}
 
 	return stringWithCharset(length, charset)
@@ -249,6 +262,7 @@ func randomInt(min, max int) int {
 	if max <= 0 {
 		max = 1
 	}
-
-	return seededRand.Intn(max-min) + min
+	rng := seededRandPool.Get().(*rand.Rand)
+	defer seededRandPool.Put(rng)
+	return rng.Intn(max-min) + min
 }
diff --git a/runner/calldata_test.go b/runner/calldata_test.go
index b5404d8b..cd0effda 100644
--- a/runner/calldata_test.go
+++ b/runner/calldata_test.go
@@ -332,3 +332,14 @@ func TestCallTemplateData_ExecuteFuncs(t *testing.T) {
 		assert.Equal(t, `{"trace_id":"ABCABCABC"}`, string(r))
 	})
 }
+
+func BenchmarkCallData_randomString(b *testing.B) {
+	b.N = 100000000
+	b.SetParallelism(1024)
+	b.RunParallel(func(pb *testing.PB) {
+		for pb.Next() {
+			_ = randomString(10)
+		}
+	})
+	b.Logf("pass")
+}