Session Not Getting Cleared In Yii

I have a strange problem. I have a web application build in Yii.

Whenever i logout from the application the user is returned to the home page. However if i refresh the page. the user is logged in again.

Here is config file

'session' => array(





and here is my logout code





Recently i noticed a file called session-1.1.8 in the runtime folder. it is not getting deleted at time of logout. how ever if i delete it manually,then user is logged out permanently.

So my Question is

1)Is there anything i am doing wrong here?

2)What is this "session-1.1.8" file ?

3)How can i remove this file programatically ?/(How can i logout permanently)

ok. I think this file is coming when i am giving the session as CDbHttpSession, When I am giving CHttpSession, it is not coming. So i hope i cannot remove that file as details of all users session will be placed here.