diff --git a/connection_pool.go b/connection_pool.go
index c41645ca..5e82305a 100644
--- a/connection_pool.go
+++ b/connection_pool.go
@@ -27,7 +27,7 @@ type ConnectionPool struct {
 	hostIndex             int
 	log                   Logger
 	rwLock                sync.RWMutex
-	cleanerChan           chan struct{} //notify when pool is close
+	cleanerChan           chan struct{} // notify when pool is close
 	closed                bool
 	sslConfig             *tls.Config
 }
@@ -111,15 +111,14 @@ func (pool *ConnectionPool) GetSession(username, password string) (*Session, err
 	resp, err := conn.authenticate(username, password)
 	if err != nil {
 		// if authentication failed, put connection back
-		pool.rwLock.Lock()
-		defer pool.rwLock.Unlock()
-		removeFromList(&pool.activeConnectionQueue, conn)
-		pool.idleConnectionQueue.PushBack(conn)
+		pool.pushBack(conn)
 		return nil, err
 	}
 
 	// Check auth response
 	if resp.GetErrorCode() != nebula.ErrorCode_SUCCEEDED {
+		// if authentication responded with unsuccessful code, put connection back
+		pool.pushBack(conn)
 		return nil, fmt.Errorf("failed to authenticate, error code: %d, error msg: %s",
 			resp.GetErrorCode(), resp.GetErrorMsg())
 	}
@@ -147,7 +146,7 @@ func (pool *ConnectionPool) getIdleConn() (*connection, error) {
 	if pool.idleConnectionQueue.Len() > 0 {
 		var newConn *connection = nil
 		var newEle *list.Element = nil
-		var tmpNextEle *list.Element = nil
+		var tmpNextEle *list.Element
 		for ele := pool.idleConnectionQueue.Front(); ele != nil; ele = tmpNextEle {
 			// Check if connection is valid
 			if res := ele.Value.(*connection).ping(); res {
@@ -177,19 +176,26 @@ func (pool *ConnectionPool) getIdleConn() (*connection, error) {
 
 // Release connection to pool
 func (pool *ConnectionPool) release(conn *connection) {
-	pool.releaseAndBack(conn, true)
+	pool.deactivate(conn, true, true)
+}
+
+func (pool *ConnectionPool) pushBack(conn *connection) {
+	pool.deactivate(conn, true, false)
 }
 
-func (pool *ConnectionPool) releaseAndBack(conn *connection, pushBack bool) {
+// Deactivate connection. Add to idleConnectionQueue if pushBack is true.
+// Release connection if release is true.
+func (pool *ConnectionPool) deactivate(conn *connection, pushBack, release bool) {
 	pool.rwLock.Lock()
 	defer pool.rwLock.Unlock()
 	// Remove connection from active queue and add into idle queue
 	removeFromList(&pool.activeConnectionQueue, conn)
-	if !pushBack {
-		return
+	if release {
+		conn.release()
+	}
+	if pushBack {
+		pool.idleConnectionQueue.PushBack(conn)
 	}
-	conn.release()
-	pool.idleConnectionQueue.PushBack(conn)
 }
 
 // Ping checks availability of host
@@ -202,7 +208,7 @@ func (pool *ConnectionPool) Close() {
 	pool.rwLock.Lock()
 	defer pool.rwLock.Unlock()
 
-	//TODO(Aiee) merge 2 lists and close all connections
+	// TODO(Aiee) merge 2 lists and close all connections
 	idleLen := pool.idleConnectionQueue.Len()
 	activeLen := pool.activeConnectionQueue.Len()
 
@@ -324,10 +330,9 @@ func (pool *ConnectionPool) connectionCleaner() {
 }
 
 func (pool *ConnectionPool) timeoutConnectionList() (closing []*connection) {
-
 	if pool.conf.IdleTime > 0 {
 		expiredSince := time.Now().Add(-pool.conf.IdleTime)
-		var newEle *list.Element = nil
+		var newEle *list.Element
 
 		maxCleanSize := pool.idleConnectionQueue.Len() + pool.activeConnectionQueue.Len() - pool.conf.MinConnPoolSize
 
@@ -353,9 +358,11 @@ func (pool *ConnectionPool) timeoutConnectionList() (closing []*connection) {
 // checkAddresses checks addresses availability
 // It opens a temporary connection to each address and closes it immediately.
 // If no error is returned, the addresses are available.
-func checkAddresses(confTimeout time.Duration, addresses []HostAddress, sslConfig *tls.Config,
-	useHTTP2 bool, httpHeader http.Header, handshakeKey string) error {
-	var timeout = 3 * time.Second
+func checkAddresses(
+	confTimeout time.Duration, addresses []HostAddress, sslConfig *tls.Config,
+	useHTTP2 bool, httpHeader http.Header, handshakeKey string,
+) error {
+	timeout := 3 * time.Second
 	if confTimeout != 0 && confTimeout < timeout {
 		timeout = confTimeout
 	}
@@ -367,8 +374,10 @@ func checkAddresses(confTimeout time.Duration, addresses []HostAddress, sslConfi
 	return nil
 }
 
-func pingAddress(address HostAddress, timeout time.Duration, sslConfig *tls.Config,
-	useHTTP2 bool, httpHeader http.Header, handshakeKey string) error {
+func pingAddress(
+	address HostAddress, timeout time.Duration, sslConfig *tls.Config,
+	useHTTP2 bool, httpHeader http.Header, handshakeKey string,
+) error {
 	newConn := newConnection(address)
 	// Open connection to host
 	if err := newConn.open(newConn.severAddress, timeout, sslConfig, useHTTP2, httpHeader, handshakeKey); err != nil {
diff --git a/session.go b/session.go
index 408cd6a8..3ceccd61 100644
--- a/session.go
+++ b/session.go
@@ -49,7 +49,6 @@ func (session *Session) executeWithReconnect(f func() (interface{}, error)) (int
 	}
 	// Execute with the new connection
 	return f()
-
 }
 
 // ExecuteWithParameter returns the result of the given query as a ResultSet
@@ -81,7 +80,6 @@ func (session *Session) ExecuteWithParameter(stmt string, params map[string]inte
 		return nil, err
 	}
 	return resp.(*ResultSet), err
-
 }
 
 // Execute returns the result of the given query as a ResultSet
@@ -219,7 +217,7 @@ func (session *Session) CreateSpace(conf SpaceConf) (*ResultSet, error) {
 		conf.VidType = "FIXED_STRING(8)"
 	}
 
-	q := ""
+	var q string
 	if conf.IgnoreIfExists {
 		q = fmt.Sprintf(
 			"CREATE SPACE IF NOT EXISTS %s (partition_num = %d, replica_factor = %d, vid_type = %s)",
@@ -264,7 +262,7 @@ func (session *Session) reConnect() error {
 		return err
 	}
 
-	session.connPool.releaseAndBack(session.connection, false)
+	session.connPool.deactivate(session.connection, false, false)
 	session.connection = newConnection
 	return nil
 }