Efficiently maintaining availability in the presence of partitionings in distributed systems

A new approach is presented for handling partitionings in replicated distributed databases. Mechanisms are developed through which transactions can access replicated data objects and observe delays similar to nonreplicated systems while enjoying the availability benefits of replication. The replication control protocol, called VELOS, achieves optimal availability, according to a well-known metric, while ensuring one-copy serializability. It is shown to provide better availability than other methods which meet the same optimality criterion. It offers these availability characteristics without relying on system transactions that must execute to restore availability, when failures and recoveries occur, but which introduce significant delays to user transactions