A delay-optimal quorum-based mutual exclusion algorithm for distributed systems

The performance of a mutual exclusion algorithm is measured by the number of messages exchanged per critical section execution and the delay between successive executions of the critical section. There is a message complexity and synchronization delay trade-off in mutual exclusion algorithms. The Lamport algorithm and the Ricart-Agrawal algorithm both have a synchronization delay of T (T is the average message delay), but their message complexity is O(N). Maekawa's algorithm reduces the message complexity to O(√N); however, it increases the synchronization delay to 2T. After Maekawa's algorithm, many quorum-based mutual exclusion algorithms have been proposed to reduce the message complexity or the increase the resiliency to site and communication link failures. Since these algorithms are Maekawa-type algorithms, they also suffer from the long synchronization delay. In this paper, we propose a delay-optimal quorum-based mutual exclusion algorithm which reduces the synchronization delay to T and still has a low message complexity of O(K) (K is the size of the quorum which can be as low as log N). A correctness proof and a detailed performance analysis are provided.