diff --git a/engine.go b/engine.go
index 33595aa9..10dce15a 100644
--- a/engine.go
+++ b/engine.go
@@ -18,23 +18,32 @@ import (
 // Engine is the major struct of xorm, it means a database manager.
 // Commonly, an application only need one engine
 type Engine struct {
-	ColumnMapper   core.IMapper
-	TableMapper    core.IMapper
-	TagIdentifier  string
-	DriverName     string
-	DataSourceName string
-	dialect        core.Dialect
-	Tables         map[reflect.Type]*core.Table
+	db      *core.DB
+	dialect core.Dialect
+
+	ColumnMapper  core.IMapper
+	TableMapper   core.IMapper
+	TagIdentifier string
+	Tables        map[reflect.Type]*core.Table
+
+	mutex  *sync.RWMutex
+	Cacher core.Cacher
 
-	mutex     *sync.RWMutex
 	ShowSQL   bool
 	ShowErr   bool
 	ShowDebug bool
 	ShowWarn  bool
-	Pool      IConnectPool
-	Filters   []core.Filter
-	Logger    ILogger // io.Writer
-	Cacher    core.Cacher
+	//Pool      IConnectPool
+	//Filters []core.Filter
+	Logger ILogger // io.Writer
+}
+
+func (engine *Engine) DriverName() string {
+	return engine.dialect.DriverName()
+}
+
+func (engine *Engine) DataSourceName() string {
+	return engine.dialect.DataSourceName()
 }
 
 func (engine *Engine) SetMapper(mapper core.IMapper) {
@@ -80,19 +89,19 @@ func (engine *Engine) AutoIncrStr() string {
 }
 
 // Set engine's pool, the pool default is Go's standard library's connection pool.
-func (engine *Engine) SetPool(pool IConnectPool) error {
+/*func (engine *Engine) SetPool(pool IConnectPool) error {
 	engine.Pool = pool
 	return engine.Pool.Init(engine)
-}
+}*/
 
 // SetMaxConns is only available for go 1.2+
 func (engine *Engine) SetMaxConns(conns int) {
-	engine.Pool.SetMaxConns(conns)
+	engine.db.SetMaxOpenConns(conns)
 }
 
 // SetMaxIdleConns
 func (engine *Engine) SetMaxIdleConns(conns int) {
-	engine.Pool.SetMaxIdleConns(conns)
+	engine.db.SetMaxIdleConns(conns)
 }
 
 // SetDefaltCacher set the default cacher. Xorm's default not enable cacher.
@@ -122,8 +131,12 @@ func (engine *Engine) MapCacher(bean interface{}, cacher core.Cacher) {
 }
 
 // OpenDB provides a interface to operate database directly.
-func (engine *Engine) OpenDB() (*core.DB, error) {
-	return core.Open(engine.DriverName, engine.DataSourceName)
+func (engine *Engine) NewDB() (*core.DB, error) {
+	return core.OpenDialect(engine.dialect)
+}
+
+func (engine *Engine) DB() *core.DB {
+	return engine.db
 }
 
 // New a session
@@ -135,7 +148,7 @@ func (engine *Engine) NewSession() *Session {
 
 // Close the engine
 func (engine *Engine) Close() error {
-	return engine.Pool.Close(engine)
+	return engine.db.Close()
 }
 
 // Ping tests if database is alive.
diff --git a/pool.go b/pool.go
deleted file mode 100644
index 919ea380..00000000
--- a/pool.go
+++ /dev/null
@@ -1,285 +0,0 @@
-package xorm
-
-import (
-	"container/list"
-	"reflect"
-	"sync"
-	"time"
-
-	"github.com/go-xorm/core"
-)
-
-// Interface IConnecPool is a connection pool interface, all implements should implement
-// Init, RetrieveDB, ReleaseDB and Close methods.
-// Init for init when engine be created or invoke SetPool
-// RetrieveDB for requesting a connection to db;
-// ReleaseDB for releasing a db connection;
-// Close for invoking when engine.Close
-type IConnectPool interface {
-	Init(engine *Engine) error
-	RetrieveDB(engine *Engine) (*core.DB, error)
-	ReleaseDB(engine *Engine, db *core.DB)
-	Close(engine *Engine) error
-	SetMaxIdleConns(conns int)
-	MaxIdleConns() int
-	SetMaxConns(conns int)
-	MaxConns() int
-}
-
-// Struct NoneConnectPool is a implement for IConnectPool. It provides directly invoke driver's
-// open and release connection function
-type NoneConnectPool struct {
-}
-
-// NewNoneConnectPool new a NoneConnectPool.
-func NewNoneConnectPool() IConnectPool {
-	return &NoneConnectPool{}
-}
-
-// Init do nothing
-func (p *NoneConnectPool) Init(engine *Engine) error {
-	return nil
-}
-
-// RetrieveDB directly open a connection
-func (p *NoneConnectPool) RetrieveDB(engine *Engine) (db *core.DB, err error) {
-	db, err = engine.OpenDB()
-	return
-}
-
-// ReleaseDB directly close a connection
-func (p *NoneConnectPool) ReleaseDB(engine *Engine, db *core.DB) {
-	db.Close()
-}
-
-// Close do nothing
-func (p *NoneConnectPool) Close(engine *Engine) error {
-	return nil
-}
-
-func (p *NoneConnectPool) SetMaxIdleConns(conns int) {
-}
-
-func (p *NoneConnectPool) MaxIdleConns() int {
-	return 0
-}
-
-// not implemented
-func (p *NoneConnectPool) SetMaxConns(conns int) {
-}
-
-// not implemented
-func (p *NoneConnectPool) MaxConns() int {
-	return -1
-}
-
-// Struct SysConnectPool is a simple wrapper for using system default connection pool.
-// About the system connection pool, you can review the code database/sql/sql.go
-// It's currently default Pool implments.
-type SysConnectPool struct {
-	db           *core.DB
-	maxIdleConns int
-	maxConns     int
-	curConns     int
-	mutex        *sync.Mutex
-	queue        *list.List
-}
-
-// NewSysConnectPool new a SysConnectPool.
-func NewSysConnectPool() IConnectPool {
-	return &SysConnectPool{}
-}
-
-// Init create a db immediately and keep it util engine closed.
-func (s *SysConnectPool) Init(engine *Engine) error {
-	db, err := engine.OpenDB()
-	if err != nil {
-		return err
-	}
-	s.db = db
-	s.maxIdleConns = 2
-	s.maxConns = -1
-	s.curConns = 0
-	s.mutex = &sync.Mutex{}
-	s.queue = list.New()
-	return nil
-}
-
-type node struct {
-	mutex sync.Mutex
-	cond  *sync.Cond
-}
-
-func newCondNode() *node {
-	n := &node{}
-	n.cond = sync.NewCond(&n.mutex)
-	return n
-}
-
-// RetrieveDB just return the only db
-func (s *SysConnectPool) RetrieveDB(engine *Engine) (db *core.DB, err error) {
-	/*if s.maxConns > 0 {
-	    fmt.Println("before retrieve")
-	    s.mutex.Lock()
-	    for s.curConns >= s.maxConns {
-	        fmt.Println("before waiting...", s.curConns, s.queue.Len())
-	        s.mutex.Unlock()
-	        n := NewNode()
-	        n.cond.L.Lock()
-	        s.queue.PushBack(n)
-	        n.cond.Wait()
-	        n.cond.L.Unlock()
-	        s.mutex.Lock()
-	        fmt.Println("after waiting...", s.curConns, s.queue.Len())
-	    }
-	    s.curConns += 1
-	    s.mutex.Unlock()
-	    fmt.Println("after retrieve")
-	}*/
-	return s.db, nil
-}
-
-// ReleaseDB do nothing
-func (s *SysConnectPool) ReleaseDB(engine *Engine, db *core.DB) {
-	/*if s.maxConns > 0 {
-	    s.mutex.Lock()
-	    fmt.Println("before release", s.queue.Len())
-	    s.curConns -= 1
-
-	    if e := s.queue.Front(); e != nil {
-	        n := e.Value.(*node)
-	        //n.cond.L.Lock()
-	        n.cond.Signal()
-	        fmt.Println("signaled...")
-	        s.queue.Remove(e)
-	        //n.cond.L.Unlock()
-	    }
-	    fmt.Println("after released", s.queue.Len())
-	    s.mutex.Unlock()
-	}*/
-}
-
-// Close closed the only db
-func (p *SysConnectPool) Close(engine *Engine) error {
-	return p.db.Close()
-}
-
-func (p *SysConnectPool) SetMaxIdleConns(conns int) {
-	p.db.SetMaxIdleConns(conns)
-	p.maxIdleConns = conns
-}
-
-func (p *SysConnectPool) MaxIdleConns() int {
-	return p.maxIdleConns
-}
-
-// not implemented
-func (p *SysConnectPool) SetMaxConns(conns int) {
-	p.maxConns = conns
-	// if support SetMaxOpenConns, go 1.2+, then set
-	if reflect.ValueOf(p.db).MethodByName("SetMaxOpenConns").IsValid() {
-		reflect.ValueOf(p.db).MethodByName("SetMaxOpenConns").Call([]reflect.Value{reflect.ValueOf(conns)})
-	}
-	//p.db.SetMaxOpenConns(conns)
-}
-
-// not implemented
-func (p *SysConnectPool) MaxConns() int {
-	return p.maxConns
-}
-
-// NewSimpleConnectPool new a SimpleConnectPool
-func NewSimpleConnectPool() IConnectPool {
-	return &SimpleConnectPool{releasedConnects: make([]*core.DB, 10),
-		usingConnects:  map[*core.DB]time.Time{},
-		cur:            -1,
-		maxWaitTimeOut: 14400,
-		maxIdleConns:   10,
-		mutex:          &sync.Mutex{},
-	}
-}
-
-// Struct SimpleConnectPool is a simple implementation for IConnectPool.
-// It's a custom connection pool and not use system connection pool.
-// Opening or Closing a database connection must be enter a lock.
-// This implements will be improved in furture.
-type SimpleConnectPool struct {
-	releasedConnects []*core.DB
-	cur              int
-	usingConnects    map[*core.DB]time.Time
-	maxWaitTimeOut   int
-	mutex            *sync.Mutex
-	maxIdleConns     int
-}
-
-func (s *SimpleConnectPool) Init(engine *Engine) error {
-	return nil
-}
-
-// RetrieveDB get a connection from connection pool
-func (p *SimpleConnectPool) RetrieveDB(engine *Engine) (*core.DB, error) {
-	p.mutex.Lock()
-	defer p.mutex.Unlock()
-	var db *core.DB = nil
-	var err error = nil
-	//fmt.Printf("%x, rbegin - released:%v, using:%v\n", &p, p.cur+1, len(p.usingConnects))
-	if p.cur < 0 {
-		db, err = engine.OpenDB()
-		if err != nil {
-			return nil, err
-		}
-		p.usingConnects[db] = time.Now()
-	} else {
-		db = p.releasedConnects[p.cur]
-		p.usingConnects[db] = time.Now()
-		p.releasedConnects[p.cur] = nil
-		p.cur = p.cur - 1
-	}
-
-	//fmt.Printf("%x, rend - released:%v, using:%v\n", &p, p.cur+1, len(p.usingConnects))
-	return db, nil
-}
-
-// ReleaseDB release a db from connection pool
-func (p *SimpleConnectPool) ReleaseDB(engine *Engine, db *core.DB) {
-	p.mutex.Lock()
-	defer p.mutex.Unlock()
-	//fmt.Printf("%x, lbegin - released:%v, using:%v\n", &p, p.cur+1, len(p.usingConnects))
-	if p.cur >= p.maxIdleConns-1 {
-		db.Close()
-	} else {
-		p.cur = p.cur + 1
-		p.releasedConnects[p.cur] = db
-	}
-	delete(p.usingConnects, db)
-	//fmt.Printf("%x, lend - released:%v, using:%v\n", &p, p.cur+1, len(p.usingConnects))
-}
-
-// Close release all db
-func (p *SimpleConnectPool) Close(engine *Engine) error {
-	p.mutex.Lock()
-	defer p.mutex.Unlock()
-	for len(p.releasedConnects) > 0 {
-		p.releasedConnects[0].Close()
-		p.releasedConnects = p.releasedConnects[1:]
-	}
-
-	return nil
-}
-
-func (p *SimpleConnectPool) SetMaxIdleConns(conns int) {
-	p.maxIdleConns = conns
-}
-
-func (p *SimpleConnectPool) MaxIdleConns() int {
-	return p.maxIdleConns
-}
-
-// not implemented
-func (p *SimpleConnectPool) SetMaxConns(conns int) {
-}
-
-// not implemented
-func (p *SimpleConnectPool) MaxConns() int {
-	return -1
-}
diff --git a/rows.go b/rows.go
index 1a176d7d..99f724dd 100644
--- a/rows.go
+++ b/rows.go
@@ -42,7 +42,7 @@ func newRows(session *Session, bean interface{}) (*Rows, error) {
 		args = rows.session.Statement.RawParams
 	}
 
-	for _, filter := range rows.session.Engine.Filters {
+	for _, filter := range rows.session.Engine.dialect.Filters() {
 		sqlStr = filter.Do(sqlStr, session.Engine.dialect, rows.session.Statement.RefTable)
 	}
 
diff --git a/session.go b/session.go
index c94e89aa..8649584a 100644
--- a/session.go
+++ b/session.go
@@ -61,7 +61,7 @@ func (session *Session) Close() {
 	}
 
 	if session.Db != nil {
-		session.Engine.Pool.ReleaseDB(session.Engine, session.Db)
+		//session.Engine.Pool.ReleaseDB(session.Engine, session.Db)
 		session.Db = nil
 		session.Tx = nil
 		session.stmtCache = nil
@@ -267,11 +267,11 @@ func (session *Session) Having(conditions string) *Session {
 
 func (session *Session) newDb() error {
 	if session.Db == nil {
-		db, err := session.Engine.Pool.RetrieveDB(session.Engine)
+		/*db, err := session.Engine.Pool.RetrieveDB(session.Engine)
 		if err != nil {
 			return err
-		}
-		session.Db = db
+		}*/
+		session.Db = session.Engine.db
 		session.stmtCache = make(map[uint32]*core.Stmt, 0)
 	}
 	return nil
@@ -426,7 +426,7 @@ func (session *Session) innerExec(sqlStr string, args ...interface{}) (sql.Resul
 }
 
 func (session *Session) exec(sqlStr string, args ...interface{}) (sql.Result, error) {
-	for _, filter := range session.Engine.Filters {
+	for _, filter := range session.Engine.dialect.Filters() {
 		sqlStr = filter.Do(sqlStr, session.Engine.dialect, session.Statement.RefTable)
 	}
 
@@ -612,7 +612,7 @@ func (session *Session) cacheGet(bean interface{}, sqlStr string, args ...interf
 	if session.Statement.RefTable == nil || len(session.Statement.RefTable.PrimaryKeys) != 1 {
 		return false, ErrCacheFailed
 	}
-	for _, filter := range session.Engine.Filters {
+	for _, filter := range session.Engine.dialect.Filters() {
 		sqlStr = filter.Do(sqlStr, session.Engine.dialect, session.Statement.RefTable)
 	}
 	newsql := session.Statement.convertIdSql(sqlStr)
@@ -699,7 +699,7 @@ func (session *Session) cacheFind(t reflect.Type, sqlStr string, rowsSlicePtr in
 		return ErrCacheFailed
 	}
 
-	for _, filter := range session.Engine.Filters {
+	for _, filter := range session.Engine.dialect.Filters() {
 		sqlStr = filter.Do(sqlStr, session.Engine.dialect, session.Statement.RefTable)
 	}
 
@@ -1709,7 +1709,7 @@ func (session *Session) row2Bean(rows *core.Rows, fields []string, fieldsCount i
 }
 
 func (session *Session) queryPreprocess(sqlStr *string, paramStr ...interface{}) {
-	for _, filter := range session.Engine.Filters {
+	for _, filter := range session.Engine.dialect.Filters() {
 		*sqlStr = filter.Do(*sqlStr, session.Engine.dialect, session.Statement.RefTable)
 	}
 
@@ -2263,7 +2263,7 @@ func (session *Session) bytes2Value(col *core.Column, fieldValue *reflect.Value,
 			var err error
 			// for mysql, when use bit, it returned \x01
 			if col.SQLType.Name == core.Bit &&
-				strings.Contains(session.Engine.DriverName, "mysql") {
+				strings.Contains(session.Engine.DriverName(), "mysql") {
 				if len(data) == 1 {
 					x = int64(data[0])
 				} else {
@@ -2289,7 +2289,7 @@ func (session *Session) bytes2Value(col *core.Column, fieldValue *reflect.Value,
 			var err error
 			// for mysql, when use bit, it returned \x01
 			if col.SQLType.Name == core.Bit &&
-				strings.Contains(session.Engine.DriverName, "mysql") {
+				strings.Contains(session.Engine.DriverName(), "mysql") {
 				if len(data) == 1 {
 					x = int(data[0])
 				} else {
@@ -2347,7 +2347,7 @@ func (session *Session) bytes2Value(col *core.Column, fieldValue *reflect.Value,
 			var err error
 			// for mysql, when use bit, it returned \x01
 			if col.SQLType.Name == core.Bit &&
-				strings.Contains(session.Engine.DriverName, "mysql") {
+				strings.Contains(session.Engine.DriverName(), "mysql") {
 				if len(data) == 1 {
 					x = int8(data[0])
 				} else {
@@ -2376,7 +2376,7 @@ func (session *Session) bytes2Value(col *core.Column, fieldValue *reflect.Value,
 			var err error
 			// for mysql, when use bit, it returned \x01
 			if col.SQLType.Name == core.Bit &&
-				strings.Contains(session.Engine.DriverName, "mysql") {
+				strings.Contains(session.Engine.DriverName(), "mysql") {
 				if len(data) == 1 {
 					x = int16(data[0])
 				} else {
@@ -2583,7 +2583,7 @@ func (session *Session) innerInsert(bean interface{}) (int64, error) {
 	// for postgres, many of them didn't implement lastInsertId, so we should
 	// implemented it ourself.
 
-	if session.Engine.DriverName != core.POSTGRES || table.AutoIncrement == "" {
+	if session.Engine.DriverName() != core.POSTGRES || table.AutoIncrement == "" {
 		res, err := session.exec(sqlStr, args...)
 		if err != nil {
 			return 0, err
@@ -2782,7 +2782,7 @@ func (session *Session) cacheUpdate(sqlStr string, args ...interface{}) error {
 	if newsql == "" {
 		return ErrCacheFailed
 	}
-	for _, filter := range session.Engine.Filters {
+	for _, filter := range session.Engine.dialect.Filters() {
 		newsql = filter.Do(newsql, session.Engine.dialect, session.Statement.RefTable)
 	}
 	session.Engine.LogDebug("[xorm:cacheUpdate] new sql", oldhead, newsql)
@@ -3085,7 +3085,7 @@ func (session *Session) cacheDelete(sqlStr string, args ...interface{}) error {
 		return ErrCacheFailed
 	}
 
-	for _, filter := range session.Engine.Filters {
+	for _, filter := range session.Engine.dialect.Filters() {
 		sqlStr = filter.Do(sqlStr, session.Engine.dialect, session.Statement.RefTable)
 	}
 
diff --git a/xorm.go b/xorm.go
index 2b059a09..8e4346ee 100644
--- a/xorm.go
+++ b/xorm.go
@@ -69,39 +69,35 @@ func NewEngine(driverName string, dataSourceName string) (*Engine, error) {
 		return nil, err
 	}
 
+	db, err := core.OpenDialect(dialect)
+	if err != nil {
+		return nil, err
+	}
+
 	engine := &Engine{
-		DriverName:     driverName,
-		DataSourceName: dataSourceName,
-		dialect:        dialect,
+		db:            db,
+		dialect:       dialect,
+		Tables:        make(map[reflect.Type]*core.Table),
+		mutex:         &sync.RWMutex{},
+		TagIdentifier: "xorm",
+		Logger:        NewSimpleLogger(os.Stdout),
 	}
 
 	engine.SetMapper(core.NewCacheMapper(new(core.SnakeMapper)))
 
-	engine.Filters = dialect.Filters()
-
-	engine.Tables = make(map[reflect.Type]*core.Table)
-
-	engine.mutex = &sync.RWMutex{}
-	engine.TagIdentifier = "xorm"
-
-	engine.Logger = NewSimpleLogger(os.Stdout)
-
-	//engine.Pool = NewSimpleConnectPool()
-	//engine.Pool = NewNoneConnectPool()
+	//engine.Filters = dialect.Filters()
 	//engine.Cacher = NewLRUCacher()
-	err = engine.SetPool(NewSysConnectPool())
+	//err = engine.SetPool(NewSysConnectPool())
+
 	runtime.SetFinalizer(engine, close)
 	return engine, err
 }
 
-// func NewLRUCacher(store core.CacheStore, max int) *LRUCacher {
-// 	return NewLRUCacher(store, core.CacheExpired, core.CacheMaxMemory, max)
-// }
+// clone an engine
+func (engine *Engine) Clone() (*Engine, error) {
+	return NewEngine(engine.dialect.DriverName(), engine.dialect.DataSourceName())
+}
 
 func NewLRUCacher2(store core.CacheStore, expired time.Duration, max int) *LRUCacher {
 	return NewLRUCacher(store, expired, 0, max)
 }
-
-// func NewMemoryStore() *MemoryStore {
-// 	return NewMemoryStore()
-// }