Wide-area systems are becoming a popular infrastructure for long-running applications. Rollback- recovery, as a common technology for fault tolerance and load balance, must meet the challenges of scalability and inherent variability in such applications. Most of the rollback-recovery protocols, however, are poor in scalability. Although pessimistic message logging protocols have no such problem, their fault-free overhead sometimes is prohibitive. Aiming at good scalability and acceptable overhead, this paper introduces the concept of pessimism grain and presents a coarse-grained pessimistic message-logging scheme. The paper also evaluates the impact of pessimism grain on the performance of the recovery scheme. Experimental results show that pessimism grain is one of the key configuration parameters to reach a desired performance level. In practice, the proper pessimism grain should be selected based on the characteristics of the applications.
