Design and evaluation of a window-consistent replication service

Real-time applications typically operate under strict timing and dependability constraints. Although traditional data replication protocols provide fault tolerance, real-time guarantees require bounded overhead for managing this redundancy. This paper presents the design and evaluation of a window-consistent primary-backup replication service that provides timely availability of the repository by relaxing the consistency of the replicated data. The service guarantees controlled inconsistency by scheduling update transmissions from the primary to the backup(s); this ensures that client applications interact with a window-consistent repository when a backup must supplant a failed primary. Experiments on our prototype implementation, on a network of Intel-based PCs running RT-Mach, show that the service handles a range of client loads while maintaining bounds on temporal inconsistency.