1. A method for instrumenting an application across a distributed system, the method comprising: instrumenting a collection of subsystems from a plurality of subsystems within a distributed system comprising the plurality of subsystems, each subsystem within the distributed system traversed by transactions processed by an application utilizing the distributed system to process transactions, wherein instrumenting a given subsystem modifies that subsystem to include a sufficient amount of transaction monitoring to monitor specific transactions traversing that subsystem and the collection of subsystems comprises a subset of the plurality of subsystems, the subset chosen such that a cost associated with instrumenting the collection of subsystems is within a pre-defined cost budget and a desired reduction in transaction monitoring uncertainty in the distributed system that is attributable to the instrumentation of the collection of subsystems is achieved.