In the last couple weeks myself and some other folks I've spoken with have had the need to know how many users were connected to a particular front end. Unfortunately there's no interface to provide this sort of information, so I decided to poke around SQL to figure out what I needed to read to determine this info. With a little help from my co-worker and UC developer extrordinaire Simon Booth, we whipped up a query in a couple minutes that gives you that data:
select fe.Fqdn,c.connections from rtcdyn.dbo.FrontEnd fe join
(Select COUNT(*) as connections, FrontEndId from rtcdyn.dbo.DeliveryContext
group by FrontEndId)
To execute this, open SQL Management Studio and connect to the instance which contains your OCS databases. Click the "New Query" button and paste in the text above. Click "Execute" and you'll receive output that shows the number of connections per front end.
Of course you could extend this to tell you users names or other information, but it's a good base query to see what it takes to pull info from the OCS databases.