Distributed Concurrency Control Based on Limited Wait-Depth

The performance of high-volume transaction processing systems for business applications is determined by the degree of contention for hardware resources as well as for data. Hardware resource requirements may be met cost-effectively with a data-partitioned or shared-nothing architecture. However, the two-phase locking (2PL) concurrency control method may restrict the performance of a shared-nothing system more severely than that of a centralized system due to increased lock holding times. Deadlock detection and resolution are an added complicating factor in shared-nothing systems. In this paper, we describe distributed Wait-Depth Limited (WDL) concurrency control (CC), a locking-based distributed CC method that limits the wait-depth of blocked transactions to one, thus preventing the occurrence of deadlocks. Several implementations of distributed WDL which vary in the number of messages and the amount of information available for decision making are discussed. The performance of a generic implementation of distributed WDL is compared with distributed 2PL (with general waiting policy) and the Wound-Wait CC method through a detailed simulation. It is shown that distributed WDL behaves similarly to 2PL for low lock contention levels, but for substantial lock contention levels (caused by higher degrees of transaction concurrency), distributed WDL outperforms the other methods to a significant degree.