Checkpointing for Optimistic Concurrency Control Methods

Abstract

Restart-oriented concurrency control (CC) methods, such as optimistic CC, outperform blocking-oriented methods, such as standard two-phase locking in a high data contention environment, but this is at the cost of wasted processing due to restarts. Volatile savepoints are considered in this study as a method to reduce this wasted processing and to improve response time. There is the usual tradeoff between the checkpointing overhead and the wasted processing when a transaction is restarted. Our study shows that in a system where objects are accessed and updated uniformly during the lifetime of transactions, significant improvement in performance at high data conflict levels are attainable only when checkpointing cost is low. This implies few optimally placed checkpoints per transaction. It is observed that checkpointing may result in a significant improvement in performance when accesses to database hot-spots are deferred to the final steps of transaction execution. The parametric studies reported in this paper are facilitated by closed form analytic solutions expressing system performance, as well as an iterative solution which takes into account hardware resource contention in addition to data contention. © 1995 IEEE