How to manage the controller’s session state?
Simply we can decorate the controller class with “SessionState” attribute. [SessionState()] attribute accepts SessionStateBehaviour enumeration.
SessionStateBehaviour enumeration has the following constants.
  • SessionStateBehavior.Default - ASP.NET default logic is used to determine the session state behavior for the request.
  • SessionStateBehavior.Required – Full read-write session state behavior is enabled for the request.
  • SessionStateBehavior.ReadOnly – Read only session state is enabled for the request.
  • SessionStateBehavior.Disabled – Session state is not enabled for processing the request.

Sessionless Controller
We decorated controller class with [SessionState(SessionStateBehaviour.Disabled)] to disable the session. Important point to remember when we are disabling session of the controller, we should n’t use TempData[] Dictionary to store any values with action method controller, it uses session to store it’s values. If you use TempData[] Dictionary when session is disabled on controller it will throw an exception “The SessionStateTempDataProvider class requires session state to be enabled“.
Note: In earlier release of MVC3 (Beta) [SessionState()] attribute was refereed as  [ControllerSessionState()]