ASP.Net MVC Nhibernate Session

When moving to MVC, and now IIS7, we started having issues in that our HTTP Module that opens and closes the ISession was called on every request (static files, etc.). I wanted to avoid doing a full rewrite of NH session management, so I implemented this code in my module, to filter out everything but requests going to the mvchandler:

void context_PreRequestHandlerExecute(object sender, System.EventArgs e)
{
    HttpContext context = ((HttpApplication)sender).Context;
    Type mvcht = typeof(System.Web.Mvc.MvcHandler);
    if (context.Handler != null && context.Handler.GetType().IsAssignableFrom(mvcht))
        {
             // Code Here
        }
}

My question is, I have never used this event in the request pipline. So, are there any hidden pitfalls in doing this? Also, am I looking at a performance issue in ru开发者_开发技巧nning this check for every request? I haven't noticed anything yet, but this is a new and still small app.

Although this doesn't specifically address your question, it should be noted that the cost of opening a session is very minimal. So you may consider not even performing this check in the first place.