Concurrency control for step-decomposed transactions

A number of authors have proposed methods for increasing the throughput of transaction processing systems by decomposing transactions into steps and allowing the steps of concurrently executing transactions to be interleaved. In some proposals all interleavings are assumed to be acceptable, while in others certain interleavings are forbidden. In this paper we describe a new concurrency control that guarantees that only the allowable interleavings speciied for an application occur The concurrency control is called an assertional concurrency control (ACC). We describe its implementation within the CA-Open Ingres tm database management system and a set of experiments that were run to evaluate its eeectiveness using the TPC-C tm Benchmark Transactions. The experiments demonstrate up to 80% improvement for benchmark transactions when lock contention is high, when long running transactions are a part of the transaction suite, and/or when suucient system resources are present to support the additional concurrency that the new control makes possible. Finally, we describe a new correctness criterion for concurrent schedules, called semantic correctness, that is weaker than serializability and yet guarantees that the speciications of all transactions are met. Semantic correctness can be used in a systematic fashion to determine the allowable interleavings for a particular application. The speciication of these interleavings can serve as input to the ACC.