This question may have been answered already but why is there downtime when I recycle an app pool? Is it because recycling restarts the app pool? I know that when recycling occurs, the worker process is restarted. I thought recycling causes uninterrupted service or am I mistaken?
Yes, restarting the Application Pool flushes the JIT cache as well as briefly takes the Pool offline from a user's perspective. This means that any active connections between the user and IIS are closed, and the user has to re-establish a connection.