This article discusses the limits on requests and sessions.

What happens if my client applications exceed the limit on the number of requests, or on the number of sessions?

If the limit on requests is exceeded, the incoming requests cannot be serviced immediately and so they are placed in a temporary “Waiting Requests” queue. They remain in the queue until they can be executed. The TIBCO Data Virtualization server will not throw any exception, as waiting requests are not considered to be an error condition.

If the number of sessions is exceeded, the client will receive an exception of the type “The connection limit of … has been exceeded”. For instance, if you have set Maximum Sessions = 2, and you attempt to run three clients, the third client will fail to connect and the server will write the following  exception to the logs:
java.sql.SQLException: The connection limit of 2 has been exceeded.[dbchannel-1918008]