Query optimization to meet performance targets for wide area applications

Abstract

Recent technology advances have enabled mediated query processing with Internet accessible WebSources. A characteristic of WebSources is that their access costs exhibit transient behavior These costs depend on the network and server workloads, which are often affected by, the time of day,, day, etc. Given transient behavior, an appropriate performance target (PT) for a noisy, environment will correspond to "at least X percentage of queries will have a latency of less than T units of time". In this paper we propose an optimizer strategy that is sensitive to the objective of meeting such performance targets (PT). For each query plan, a PT sensitive optimizer uses both the expected value of the cost distribution of the plan, as well as the expected delay, of the plan. We validate our strategy using a simulation based study of the optimizers behavior. We also experimentally validate the optimizer using traces of access costs for real WebSources.