Buddy System: Available, Consistent, Durable Web Service Transactions

In this paper we investigate the problem of providing consistency, availability and durability for web service transactions. We propose an approach that matches the availability of the popular lazy replica update propagation method while increases the durability and consistency. Our replica update propagation method is called the Buddy System, which requires that updates are preserved synchronously in two replicas. Our first implementation schedules fine-grained WS transactions. In these transactions each activity is a low level database operation. Later we consider each transaction as a black box, with only the corresponding metadata, expressed as UML specifications, as transaction semantics. We refer to these WS transactions as coarse-grained WS transactions. The Buddy System is able to handle these course grained WS transactions, using UML stereotypes that allow scheduling semantics to be embedded into the design model. We show that our approach guarantees one-copy serializability, matches the performance of the lazy update propagation methods, and increases durability in the presence of hardware failures.