#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"
}