Relative Serializability: An Approach for Relaxing the Atomicity of Transactions

Serializability is too strong a correctness criterion and unnecessarily restricts concurrency. We use the semantic information of a transaction to provide different atomicity views of the transaction to other transactions. The proposed approach improves concurrency and allows interleavings among transactions which are nonserializable, but which nonetheless preserve the consistency of the database and are acceptable to the users. We develop a graph-based tool whose acyclicity is both a necessary and sufficient condition for the correctness of an execution. Our theory encompasses earlier proposals that incorporate semantic information of transactions. Furthermore, it is the first approach that provides an efficient graph-based tool for recognizing correct schedules without imposing any restrictions on the application domain. Our approach is widely applicable to many advanced database applications such as systems with long-lived transactions and collaborative environments.