When is the configuration loaded with nHibernate?

Question

I was reading that the initial load time for the configuration can be fairly long in nHibernate depending on the # of mapping tables, etc.

Is this done once and stored in session or cache?
Will it happen every time the ASP.NET process recycles?

Answer 1

The Configuration is used to build the ISessionFactory. It's a one shot deal - which will occurs at the application startup.

Answer 2

A Configuration object is normally associated to an ISessionFactory. If you have lots of mappings building (by calling cfg.BuildSessionFactory) a session factory might be slow. That's why you need to construct a session factory only once and use it throughout your entire application. In an ASP.NET application when the process recycles, you will lose the reference to this session factory and it needs to be reconstructed again.

If you find it is extremely slow to construct your session factory you could improve performance by disabling the reflection optimizer : Environment.UseReflectionOptimizer = false (cf doc)