Adaptable Recovery Using Dynamic Quorum Assignments

This research investigates the problem of how to adapt the changing of quorum assignments for objects in a replicated database to the duration and extent of failures occurring in the underlying communication network. The concept of a view based on a connected component of the network is used to coordinate changes to quorum assignments of different objects. New view formation is used only when needed, and conditions under which quorum assignments may be changed without forming a new view are given. A dynamic view formation protocol is proposed that permits objects to join a new view on demand. A new technique called inheritance enables a new view to acquire quorum assignments from an old view, 50 that only those objects that were accessed during a failure need to change their quorum assignments back following repair of the failure. Extension of an existing view may be used to incorporate a recovering site into the network without forming a new view, thus localizing the effects of the failure. We have made analytical performance estimates for some sample network configurations and failure situations to show the improvements of our method over previously proposed methods. Following repair of a failure, our method can begin processing transactions almost immediately, but with less extra average overhead than for previous methods. We describe a prototype implementation of our method that will be used for future experimentation. "This research is sponsored by National Science Foundation Grant IRl-8821398.