SMDP: minimizing buffer requirements for continuous media servers

Excessive buffer requirement to handle continuous-media playbacks is an imp ediment to cost-effective provisioning for on-line video retrieval. Given t he skewed distribution of video popularity, it is expected that often there are concurrent playbacks of the same video file within a short time interv al. This creates an opportunity to batch multiple requests and to service t hem with a single stream from the disk without violating the on-demand cons traint. However, there is a need to keep data in memory between successive uses to do this. This leads to a buffer space trade-off between servicing a request in memory mode vs. servicing it in disk-mode. In this work, we dev elop a novel algorithm to minimize the buffer requirement to support a set of concurrent playbacks. One of the beauties of the proposed scheme is that it enables the server to dynamically adapt to the changing workload while minimizing the total buffer space requirement. Our algorithm makes a signif icant contribution in decreasing the total buffer requirement, especially w hen the user access pattern is biased in favor of a small set of files. The idea of the proposed scheme is modeled in detail using an analytical formu lation, and optimality of the algorithm is proved. An analytical framework is developed so that the proposed scheme can be used in combination with va rious existing disk-scheduling strategies. Our simulation results confirm t hat under certain circumstances, it is much more resource efficient to supp ort some of the playbacks in memory mode and subsequently the proposed sche me enables the server to minimize the overall buffer space requirement.