U. Oslo

Multi-master update everywhere database replication, as achieved by protocols based on group communication such as DBSM and Postgres-R, addresses both performance and availability. By scaling it to wide area networks, one could save costly bandwidth and avoid large round-trips to a distant master server. Also, by ensuring that updates are safely stored at a remote site within transaction boundaries, disaster recovery is guaranteed. Unfortunately, scaling ex-isting cluster based replication protocols is troublesome. In this paper we present a database replication proto-col based on group communication that targets intercon-nected clusters. In contrast with previous proposals, it uses a separate multicast group for each cluster and thus does not impose any additional requirements on group commu-nication, easing implementation and deployment in a real setting. Nonetheless, the protocol ensures one-copy equiv-alence while allowing all sites to execute update transac-tions. Experimental evaluation using the workload of the industry standard TPC-C benchmark confirms the advan-tages of the approach. 1