Long-running client requests are requests where the same client can make repeated requests of a service and needs data to be preserved between invocations of the service. In Java terms, they are stateful requests. So if the client is a stateful Java bean running in an application server such as WebLogic or WebSphere, the service will run for as long as the bean runs. In these circumstances, you need more service execution processes, even if the service itself is CPU-bound rather than I/O-bound.
If the enterprise server instance detects that the request is stateful, a new service execution process is started automatically. Dynamic growth of service execution processes consumes machine resources and can affect the performance of the enterprise server. We recommend that, unless your application design actually requires stateful interaction, you keep these types of request to a minimum.