Analysis of Hybrid Concurrency Control Schemes for a High Data Contention Environment

Abstract

The performance of database transaction processing systems can be profoundly affected by the concurrency control method employed. Optimistic Concurrency Control (OCC) offers an alternative to locking, but is vulnerable to resource contention due to transaction aborts. With sufficient buffer, data blocks referenced by aborted transactions can continue to be kept in memory and be available for access during rerun, thus greatly reducing the abort probability during rerun. This buffer retention effect would make the pure OCC scheme, which only aborts a transaction at its commit time, perform better than the approach of aborting transactions as soon as conflict is detected (referred to as broadcast OCC). To exploit this phenomenon, we develop analytic models to study hybrid CC schemes which employ a different CC scheme to handle rerun transactions, since their characteristics are different from the first run of transactions. These include switching to static or dynamic locking during rerun (referred to as static and dynamic hybrid OCC schemes, respectively), and switching to broadcast OCC during rerun, while doing pure OCC for the first run. In a high data contention environment where locking is inferior to OCC, our analysis shows that the performance can be substantially improved by using this hybrid approach, and we study the trade-off of the different hybrid CC schemes. The analytic models are based on a decomposition approach and use a mean-value-type analysis. The accuracy of the analysis is validated through simulations. Ontimistic concurrency control, transaction processing, data contention, performance analysis, analytical modeling. © 1992 IEEE