1. A system for tracing distributed transactions over thread, process, server boundaries, and external messaging systems, comprising: an entry sensor positioned at a beginning of an instrumented method of the distributed transactions; an exit sensor positioned at an exit point of the instrumented method of the distributed transactions; wherein the entry sensor or the exit sensor uses a thread local storage to store and retrieve correlation information to correlate method invocations for the thread; and wherein correlation information between distributed parts of a distributed transaction is propagated as out of band signaling information.