Adaptive disk scheduling in a multimedia DBMS

Abstract

In this paper, we present APEX, a disk scheduling framework with QoS support, designed for environments with highly varying disk bandwidth usage. In particular, we focus on a Learning-on-Demand scenario supported by a multimedia database management system, where students can search for, and play back multimedia-based learning material. APEX is based on a two-level scheduling architecture, where the upper level realizes different service classes using a set of queues, while the lower level distributes available disk bandwidth among these queues.In this paper, we focus on the low-level scheduling in APEX, which is based on an extended token bucket algorithm. The disk requests scheduled for service are assembled into batches, which render possible good efficiency for the disk. Combined with a very efficient work-conservation scheme, this enables APEX to apply bandwidth where it is needed, without efficiency loss. We demonstrate, through simulations, that APEX provides both higher throughput and lower response times than other mixed-media disk schedulers, while still avoiding deadline violations for real-time requests. We also show its robustness with respect to misaligned bandwidth allocation.