1. A method for generating a resource function estimate of resource usage by an instance of a processing element configured to consume zero or more input data streams in a stream processing system having a set of available resources for the processing element to use, the method comprising: receiving at least one specified performance metric for the zero or more input data streams and a processing power of the set of available resources, wherein one of the at least one specified performance metric is stream rate; generating a multi-part signature of executable-specific information for the processing element and a multi-part signature of context-specific information for the instance of the processing element; accessing a database of resource functions to identify a static resource function corresponding to the multi-part signature of executable-specific information and a context-dependent resource function corresponding to the multi-part signature of context-specific information; combining the static resource function and the context-dependent resource function to form a composite resource function for the instance of the processing element; and applying the resource function to the at least one specified performance metric and the processing power to generate the resource function estimate of the at least one specified performance metric for processing by the instance of the processing element.