Efficient Distributed Detection of Conjunctions of Local Predicates

Global predicate detection is a fundamental problem in distributed systems and finds applications in many domains such as testing and debugging distributed programs. This paper presents two efficient distributed algorithms to detect conjunctive form global predicates in distributed systems. The algorithms detect the first consistent global state that satisfies the predicate even if the predicate is unstable. The algorithms are based on complementary approaches and are dual of each other. The algorithms are distributed because the predicate detection efforts as well as the necessary information is equally distributed among the processes. We prove the correctness of the algorithms and compare their performance with those of the existing predicate detection algorithms. The proposed algorithms compare very favorably with the existing algorithms in terms of the number of messages exchanged for predicate detection

Monitoring Partially Synchronous Distributed Systems using SMT Solvers

In this paper, we discuss the feasibility of monitoring partially synchronous distributed systems to detect latent bugs, i.e., errors caused by concurrency and race conditions among concurrent processes. We present a monitoring framework where we model both system constraints and latent bugs as Satisfiability Modulo Theories (SMT) formulas, and we detect the presence of latent bugs using an SMT solver. We demonstrate the feasibility of our framework using both synthetic applications where latent bugs occur at any time with random probability and an application involving exclusive access to a shared resource with a subtle timing bug. We illustrate how the time required for verification is affected by parameters such as communication frequency, latency, and clock skew. Our results show that our framework can be used for real-life applications, and because our framework uses SMT solvers, the range of appropriate applications will increase as these solvers become more efficient over time.Comment: Technical Report corresponding to the paper accepted at Runtime Verification (RV) 201