Counting the number of sessions in a web farm

Hi,

We have a ASP .NET application which will be deployed in a web farm.
We would like to find the total number of sessions that have been
established. If we create a counter in global.asax.cs, it will be able
to count only within aspnet_wp process. In a web farm, multiple nodes
will have IIS on multiple machines.
If we use SQL server-based session management, can we get the total
number of active session by querying the Session DB?
If we later decide to use session state server to store the sessions,
can we get the number of active sessions?

Thanks,
Yash