Optimizing in-order execution of continuous queries over streamed sensor data

In this paper we study the problem of providing ordered execution of time-based sliding window queries over input streams of sensor data with inherent delays. We present three approaches to achieve the ordered execution. The first approach enforces ordered processing at the input side of the query execution plan. In the second approach we utilize the advantage of out-of-order execution to optimize query operators and enforce an ordered release of the output results. The third approach is adaptive and switches between the first and second approaches to achieve the best overall performance with current input arrival rates and level of multiprogramming. We study the performance of the proposed approaches both analytically and experimentally while using various system configurations. Our performance study is based on an extensive set of experiments using a realization of the proposed approaches in Nile, a prototype stream query processing system.