Lamport's Algorithm Research Articles

Dynamic snapshot algorithm and partial rollback algorithm for internet agents

AbstractThis paper considers an Internet agent system in which a tremendous number of agents operate, frequently appearing and disappearing, and discusses the fault‐tolerant algorithm. Application of the snapshot algorithm to the agent system is considered. The snapshot algorithm is used to view the whole situation (snapshot) of the distributed system. The snapshot algorithm of Chandy and Lamport [2] is considered as a representative snapshot algorithm, in terms of the high efficiency and the simplicity of the procedure. It is not practical, however, to apply their snapshot algorithm to the distributed agent system in which a tremendous number of agents operate. From such a viewpoint, this paper extends the idea of Chandy and Lamport's algorithm and proposes a subsnapshot algorithm, in which the snapshot is taken among the agents who are in the causal relation, through message exchange and agent creation. Then, an efficient rollback algorithm is proposed, which is based on the snapshots taken by the subsnapshot algorithm. In the general rollback algorithm utilizing the snapshot, all agents must roll back. In contrast, in the rollback algorithm proposed in this paper, it suffices that only some agents should roll back. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 3, 88(12): 43–57, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjc.20208

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 (1978) and the Ricart-Agrawal algorithm (1981) 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(/spl radic/N); however, it increases the synchronization delay to 2T. After Maekawa's algorithm (1985), 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. 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.

Implementing multiple locks using Lamport's mutual exclusion algorithm

We describe an approach for implementing higher-level mutual-exclusion constructs using Lamport's algorithm. A straightforward implementation of, for example, monitor locks based on Lamport's algorithm requires O( n ) space per monitor lock if there are n processes that may share the lock. It has occasionally been claimed that this makes the algorithm undesirable in practice. The insight presented here is that we only need a (small) constant amount of space per lock, plus O( n ) space shared by all locks in the system. For some common applications, this adds no memory references to the implementation of the algorithm. Fully general spin-lock acquisition and release can usually be implemented with the addition of one memory reference to Lamport's algorithm. On particularly unfavorable hardware, three additional memory references may be required in the contention-free case.