RTSS ’ 94 : The 14 th IEEE Real - Time System Symposium , San Juan , Puerto

Various concurrency control algorithms diier in the time when connicts are detected, and in the way they are resolved. Pessimistic (PCC) protocols detect connicts as soon as they occur and resolve them using blocking. Optimistic (OCC) protocols detect connicts at transaction commit time and resolve them using rollbacks. For real-time databases, blockages and rollbacks are hazards that increase the likelihood of transactions missing their deadlines. We propose a Speculative Concurrency Control (SCC) technique that minimizes the impact of blockages and rollbacks. SCC relies on added system resources to speculate on potential serialization orders, ensuring that if such serialization orders materialize, the hazards of blockages and roll-backs are minimized. We present a number of SCC-based algorithms that diier in the level of speculation they introduce, and the amount of system resources (mainly memory) they require. We show the performance gains (in terms of number of sat-issed timing constraints) to be expected when a representative SCC algorithm (SCC-2S) is adopted.