An O(1) quorum consensus protocol tailored for the client/server architecture

In a client/server architecture, replicated copies of an object are assigned to different servers (possibly client sites) in order to increase the availability of the database in case some but not all servers fail. A highly efficient, highly reliable quorum consensus protocol, the Quorum Rings protocol (QRP), specifically designed to take advantage of the client/server architecture, is introduced. The high resiliency of QRP is achieved at a very low cost in communication messages. More specifically, the number of communication messages required for a QRP read or write operation is O(1) in normal mode (when there are no failures in the system) and only O(√N) in failure mode (when some but not all servers with replicated objects are faulty). Finally, QRP exhibits the property of graceful degradation: more communication cost is incurred only when the number of failures increases in the system