#Number TR-PDS-1998-002 #Title Predicate Control for Active Debugging of Distributed Programs #Author Ashis Tarafdar Vijay K. Garg #Abstract Existing approaches to debugging distributed systems involve a cycle of passive observation followed by computation replaying. We propose predicate control as an {\em active\/} approach to debugging such systems. The predicate control approach involves a cycle of observation followed by {\em controlled\/} replaying of computations, based on observation. We formalize the predicate control problem for both off-line and on-line scenarios. We prove that off-line predicate control for general boolean predicates is NP-hard. However, we provide an efficient solution for off-line predicate control for the class of disjunctive predicates. We further solve on-line predicate control for disjunctive predicates under certain restrictions on the system. Lastly, we demonstrate how both off-line and on-line predicate control facilitate distributed debugging by allowing the programmer to control computations to maintain global safety properties. #Bib @TechReport{, author = "Ashis Tarafdar and Vijay K. Garg", title = "Predicate Control for Active Debugging of Distributed Programs", institution = "Parallel and Distributed Systems Laboratory, ECE Dept. University of Texas at Austin", year = "1998", number = "ECE-PDS-1998-002", note = "available via ftp or WWW at maple.ece.utexas.edu as technical report TR-PDS-1998-002" }