Optimizing i/o-intensive transactions in highly interactive applications

The performance provided by an interactive online database system is typically measured in terms of meeting certain pre-specified Service Level Agreements (SLAs), with expected transaction latency being the most commonly used type of SLA. This form of SLA acts as a soft deadline for each transaction, and user satisfaction can be measured in terms of minimizing tardiness, that is, the deviation from SLA. This objective is further complicated for I/O-intensive transactions, where the storage system becomes the performance bottleneck. Moreover, common I/O scheduling policies employed by the Operating System with a goal of improving I/O throughput or average latency may run counter to optimizing per-transaction performance since the Operating System is typically oblivious to the application high-level SLA specifications. In this paper, we propose a new SLA-aware policy for scheduling I/O requests of database transactions. Our proposed policy synergistically combines novel deadline-aware scheduling policies for database transactions with features of Operating System scheduling policies designed for improving I/O throughput. This enables our proposed policy to dynamically adapt to workload and consistently provide the best performance.