Eecient Detection of Global Properties in Distributed Systems Using Partial-order Methods

A new approach is presented for detecting whether a particular computation of an asyn-chronous distributed system satisses Poss (read \possibly "), meaning the system could have passed through a global state satisfying predicate , or Def (read \deenitely "), meaning the system deenitely passed through a global state satisfying. Detection can be done easily by straightforward state-space search; this is essentially what Cooper and Marzullo proposed. We show that the persistent-set technique, a well-known partial-order method for optimizing state-space search, provides eecient detection. The resulting detection algorithms handle larger classes of predicates and thus are more general than two special-purpose detection algorithms by Garg and Waldecker, which detect Poss and Def eeciently for a restricted but important class of predicates. Furthermore, our algorithm for Poss achieves the same worst-case asymptotic time complexity as Garg and Waldecker's special-purpose algorithm for Poss. We apply our algorithm for Poss to two examples, achieving a speedup of over 700 in one example and over 70 in the other, compared to unoptimized state-space search.