Speculative Concurrency Control

We describe SCC-kS, a Speculative Concurrency Control (SCC) algorithm that allows a DBMS to use e ciently the extra computing resources available in the system to increase the likelihood of timely commitment of transactions. Using SCC-kS, up to k shadow transactions execute speculatively on behalf of a given uncommitted transaction so as to protect against the hazards of blockages and restarts. SCC-kS allows the system to scale the level of speculation that each transaction is allowed to perform, thus providing a straightforward mechanism of trading resources for timeliness. Also, we describe SCC-DC, a value-cognizant SCC protocol that utilizes deadline and criticalness information to improve timeliness through the controlled deferment of transaction commitments. We present simulation results that quantify the performance gains of our protocols compared to other widely used concurrency control protocols for real-time databases.