[asp.net] IIS: Idle Timeout vs Recycle

In IIS there are two areas (well, more than two) where recycling can occur:

1. Under the "Process Model" section ? "Idle Timeout" (default 20 minutes)

and

2. Under the "Recycle" section ? "Regular Time Interval" (default 1740 minutes)

My questions are:

1. What are the differences between the two methods?
2. What are the negative implications of settings them to 0?

I have inherited a desktop app that makes calls to a series of Web Services on IIS. The web services (also) have to be able to run timed processes, independently (without having the client on). Hence they all have timers. The web service timers were shutting down (memory leak?) so we set the Idle time out to 0 and timers stay on.

IIS now has

Idle Time-out Action : Suspend setting

Suspending is just freezes the process and it is much more efficient than the destroying the process.

From here:

One way to conserve system resources is to configure idle time-out settings for the worker processes in an application pool. When these settings are configured, a worker process will shut down after a specified period of inactivity. The default value for idle time-out is 20 minutes.

Also check Why is the IIS default app pool recycle set to 1740 minutes?

If you have a just a few sites on your server and you want them to always load fast then set this to zero. Otherwise, when you have 20 minutes without any traffic then the app pool will terminate so that it can start up again on the next visit. The problem is that the first visit to an app pool needs to create a new w3wp.exe worker process which is slow because the app pool needs to be created, ASP.NET or another framework needs to be loaded, and then your application needs to be loaded. That can take a few seconds. Therefore I set that to 0 every chance I have, unless it’s for a server that hosts a lot of sites that don’t always need to be running.