diff --git a/pkg/structure/define.go b/pkg/structure/define.go
index 39f72d1..7e160fb 100644
--- a/pkg/structure/define.go
+++ b/pkg/structure/define.go
@@ -1,7 +1,7 @@
 package structure
 
 const (
-	defaultLen = 32 // 默认创建的 value 大小
+	defaultLen = 8 // 默认创建的 value 大小
 )
 
 type DynamicType int8
diff --git a/pkg/structure/value.go b/pkg/structure/value.go
index b440db1..d4fa323 100644
--- a/pkg/structure/value.go
+++ b/pkg/structure/value.go
@@ -3,10 +3,9 @@ package structure
 import (
 	"bytes"
 	"encoding/binary"
+	"gitee.com/timedb/wheatCache/pkg/errorx"
 	"math"
 	"strconv"
-
-	"gitee.com/timedb/wheatCache/pkg/errorx"
 )
 
 // Value 提供一个基础的 动态类型
@@ -26,7 +25,7 @@ func NewValue() *Value {
 }
 
 func (v *Value) GetLength() int {
-	return v.length
+	return len(v.val)
 }
 
 func (v *Value) GetDynamicType() DynamicType {
@@ -113,3 +112,10 @@ func (v *Value) InferValue(str string) {
 
 	v.SetString(str)
 }
+
+// ChangeValueLength 根据类型推断 change 的大小
+func (v *Value) ChangeValueLength(f func()) int64 {
+	startLen := v.GetLength()
+	f()
+	return int64(v.GetLength() - startLen)
+}