1-Safe Algorithms for Symmetric Site Configurations

摘要

In order to provide database availability in the presence of node and site failures, traditional 1-safe algorithms disallow primary and hot standby replicas to be located at the same site. This means that the failure of a single primary node must be handled like a failure of the entire primary site. Furthermore, this excludes symmetric site configurations, where the primary replicas are located at the site closest to the accessing clients. In this paper, we present three novel 1-safe algorithms that allow the above restrictions to be removed. The relative performance of these and the traditional algorithms are evaluated by means of simulation studies. Our main conclusion is that the restrictions of the traditional algorithms can be removed without significantly increasing the processing overhead, during normal operation. From an evaluation based on performance, availability, and transaction durability, the novel dependency tracking algorithm provides the best overall solution.