DDB: a distributed debugger based on replay

DDB is a distributed debugger that is based on the well known technique of "Instant Replay". The debugger is designed and implemented to operate under multithreaded Mach Distributed Operating System. It is complete in the sense that a graphical user interface, source code level debugging facility at the individual nodes of the distributed computation, and our experience in using the debugger are well documented. We provide, in this paper, a brief, but complete view of DDB from which the developers of new debuggers for parallel and distributed systems can benefit.