Theory of serializablity for a parallel model of transactions

In this paper we present a parallel program schema model of a transaction system and generalize the concept of serializability from the sequential two-step model to a parallel multi-step model. We define two classes of serializable executions, and for each class we discuss two problems: recognition and scheduling. It is shown that the results for the recognition and online scheduling problems for the sequential model generalize to the parallel model. But it is argued that online scheduling is not suitable for a parallel execution environment. Therefore, batch schedulers are defined and a minimal set of precedence constraints is derived. Finally, it is shown that any optimal batch scheduler that uses syntactic information alone cannot be efficient.