Load Balancing and Almost Symmetries for RAMBO Quorum Hosting

RAMBO is the Reconfigurable Atomic Memory for Basic Objects, a formally specified algorithm that implements atomic read/write shared memory in dynamic networks, where the participating hosts may join, leave, or fail. To maintain availability and consistency in such dynamic settings, RAMBO replicates objects and uses quorum systems that can be reconfigured in response to perturbations in the environment. This is accomplished by installing new quorum configurations and removing obsolete configurations, while preserving data consistency. Given the dynamic nature of the atomic memory service, it is vitally important to reconfigure the system online, while making well-reasoned selections of new quorum configurations. This paper reexamines the quorum hosting problem, concentrating on better load balancing models and a novel use of almost symmetries for breaking similarities among hosts in the target network. The resultant performance improvements allow more reasonably-sized systems to be reconfigured online in a way that optimizes hosting of quorums with respect to relevant performance criteria.