diff --git a/engine.go b/engine.go
index 7639310d..af910562 100644
--- a/engine.go
+++ b/engine.go
@@ -27,7 +27,7 @@ type Engine struct {
 	dialect        core.Dialect
 	Tables         map[reflect.Type]*core.Table
 
-	mutex        *sync.Mutex
+	mutex        *sync.RWMutex
 	ShowSQL      bool
 	ShowErr      bool
 	ShowDebug    bool
@@ -388,12 +388,14 @@ func (engine *Engine) Having(conditions string) *Session {
 }
 
 func (engine *Engine) autoMapType(t reflect.Type) *core.Table {
-	engine.mutex.Lock()
-	defer engine.mutex.Unlock()
+	engine.mutex.RLock()
 	table, ok := engine.Tables[t]
+	engine.mutex.RUnlock()
 	if !ok {
 		table = engine.mapType(t)
+		engine.mutex.Lock()
 		engine.Tables[t] = table
+		engine.mutex.Unlock()
 	}
 	return table
 }
diff --git a/xorm.go b/xorm.go
index a1f6a5d8..40653eea 100644
--- a/xorm.go
+++ b/xorm.go
@@ -50,12 +50,12 @@ func NewEngine(driverName string, dataSourceName string) (*Engine, error) {
 		DataSourceName: dataSourceName, dialect: dialect,
 		tableCachers: make(map[reflect.Type]core.Cacher)}
 
-	engine.SetMapper(core.SnakeMapper{})
+	engine.SetMapper(core.NewCacheMapper(new(core.SnakeMapper)))
 
 	engine.Filters = dialect.Filters()
 
 	engine.Tables = make(map[reflect.Type]*core.Table)
-	engine.mutex = &sync.Mutex{}
+	engine.mutex = &sync.RWMutex{}
 	engine.TagIdentifier = "xorm"
 
 	engine.Logger = os.Stdout