This demonstration presents the CoBRa Optimizer that allows efficient evaluation of global queries without having complete knowledge on data. This optimizer advantageously applies the Case Based Reasoning paradigm to the query optimization process. The CoBRa Optimizer acquires performance knowledge (other than classical metadata) while evaluating queries and exploits this knowledge for generating new execution plans for similar queries. The CoBRa Optimizer will be demonstrated simulating a scenario on our testbed platform supporting network-oriented applications. The internal state of the CoBRa Optimizer will be explored using this simulation platform.