Many of those who focus on the discipline of performance within complex distributed systems such as SOA will first steer you toward modeling. Unfortunately, we don’t know enough about how services behave to model how they will perform, so it’s a good idea to test the services that will make up your SOA before you build your performance model; otherwise, you’re just guessing.

Testing services, even proof-of-concept services, means that you simulate operational characteristics during the test, or, how you intend to leverage the service. You do this by building or buying test harnesses that can load the service as needed for testing. You should utilize low use, medium use, and high use scenarios to determine how the service behaves under an increasing load, and make sure you have some sort of monitoring mechanism to gather the data for analysis.

What you’ll find, in most cases, is that the service will reach a saturation point where performance drops off significantly as the load increases. The saturation point is largely dependent upon the patterns of the service. For instance, transactional services should be able to support a much higher load than light weight services.