diff --git a/CHANGELOG.md b/CHANGELOG.md
index 92caabb..0fe9ff2 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,9 +5,11 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
-## [1.4.5] - 2014-04-19
+## [1.4.5] - 2014-04-20
 ### Changed
 - used int64 instead of int in `Queryer.Count` (#37)
+- fixed timer performance issue (#38)
+- fixed StmtMaxIdleTime missing issue (#38)
 
 ## [1.4.4] - 2014-04-19
 ### Added
diff --git a/context_stmt.go b/context_stmt.go
index a390e6e..3c94352 100644
--- a/context_stmt.go
+++ b/context_stmt.go
@@ -65,8 +65,11 @@ func (db *Context) closeStaleStmt() {
 }
 
 func (db *Context) checkIdleStmt() {
+	delay := time.NewTicker(db.stmtMaxIdleTime)
+	defer delay.Stop()
+
 	for {
-		<-time.After(db.stmtMaxIdleTime)
+		<-delay.C
 
 		db.closeStaleStmt()
 	}
diff --git a/context_stmt_test.go b/context_stmt_test.go
index 176e992..4c51e6c 100644
--- a/context_stmt_test.go
+++ b/context_stmt_test.go
@@ -28,9 +28,11 @@ func TestStmt(t *testing.T) {
 	_, err = d.Exec("INSERT INTO `rows`(`id`) VALUES(4)")
 	require.NoError(t, err)
 
-	db := Open(d)
+	stmtMaxIdleTime := StmtMaxIdleTime
 
-	db.stmtMaxIdleTime = 1 * time.Second
+	StmtMaxIdleTime = 1 * time.Second
+	db := Open(d)
+	StmtMaxIdleTime = stmtMaxIdleTime
 
 	tests := []struct {
 		name string
@@ -123,7 +125,9 @@ func TestStmt(t *testing.T) {
 				require.NoError(t, err)
 				require.Equal(t, int64(1), affected)
 
+				db.stmtsMutex.Lock()
 				s, ok := db.stmts[q]
+				db.stmtsMutex.Unlock()
 				require.True(t, ok)
 				require.False(t, s.isUsing)
 
diff --git a/db.go b/db.go
index d7d5b84..13d8208 100644
--- a/db.go
+++ b/db.go
@@ -27,25 +27,22 @@ type DB struct {
 // Open creates a new DB instance with the provided database connections.
 func Open(dbs ...*sql.DB) *DB {
 	d := &DB{
-		Context: &Context{
-			DB:              dbs[0],
-			stmts:           make(map[string]*Stmt),
-			Index:           0,
-			stmtMaxIdleTime: StmtMaxIdleTime,
-		},
 		dhts: make(map[string]*shardid.DHT),
 	}
 
 	for i, db := range dbs {
 		ctx := &Context{
-			DB:    db,
-			Index: i,
-			stmts: make(map[string]*Stmt),
+			DB:              db,
+			Index:           i,
+			stmts:           make(map[string]*Stmt),
+			stmtMaxIdleTime: StmtMaxIdleTime,
 		}
 		d.dbs = append(d.dbs, ctx)
 		go ctx.checkIdleStmt()
 	}
 
+	d.Context = d.dbs[0]
+
 	return d
 }
 
@@ -58,9 +55,10 @@ func (db *DB) Add(dbs ...*sql.DB) {
 
 	for i, d := range dbs {
 		ctx := &Context{
-			DB:    d,
-			Index: n + i,
-			stmts: make(map[string]*Stmt),
+			DB:              d,
+			Index:           n + i,
+			stmts:           make(map[string]*Stmt),
+			stmtMaxIdleTime: StmtMaxIdleTime,
 		}
 		db.dbs = append(db.dbs, ctx)
 		go ctx.checkIdleStmt()