code: func (v *mvccValue) UnmarshalBinary(data []byte) error {
  	var mh marshalHelper
  	buf := bytes.NewBuffer(data)
  	var vt int64
  	mh.ReadNumber(buf, &vt)
  	v.valueType = mvccValueType(vt)
  	mh.ReadNumber(buf, &v.startTS)
  	mh.ReadNumber(buf, &v.commitTS)
  	mh.ReadSlice(buf, &v.value)
  	return errors.Trace(mh.err)
  }
docs: // UnmarshalBinary implements encoding.BinaryUnmarshaler interface.