Application_Start and Application_End Event execution time

Application_Start: The first user to access the site will trigger the method. Some system variables are usually defined in this method, such as the total number of online chat rooms, the initialization of historical visitor demographics, and so on.

Application_End: This method is triggered when a Web site is closed or restarted.
Session_Start: triggered when each user accesses the first page of a website;

Session_End: Session.Abandon () is used, or the session timeout is triggered after the user exits.

In this case, when your IIS is configured, the first person, the first time you visit this site, two are triggered. Applicaiton in front, session in the back,
Later, as long as your IIS process does not restart or crash, when someone visits the site, it only executes session_stat.

That is Applicaiton_state () is only triggered when you start the program, as long as your site is running, it will not be triggered.
The session is associated with a user, and it is triggered once by a new user.
Concrete, the landlord can follow a breakpoint, their own debugging can be.