Lira: Lightweight, Region-aware Load Shedding in Mobile CQ Systems

To provide high-quality results for location-based, continual queries (CQs) in a mobile system, the query processor usually demands receiving frequent position updates from the mobile nodes. However, processing frequent updates often causes the query processor to become overloaded, under which updates must be dropped randomly, bringing down the query-result accuracy and negating the benefits of frequent updates. In this paper, we develop LIRA - a lightweight, region-aware load-shedding technique for preventively reducing the position-update load of a query processor, while maintaining high-quality query results. Instead of receiving too many updates and then randomly dropping some of them, LIRA uses a region-aware partitioning mechanism to identify the most beneficial shedding regions to cut down the position updates sent by the mobile nodes within those regions. Based on the densities of mobile nodes and queries in a region, LIRA judiciously applies different amounts of update reduction for different regions, aiming to minimize the negative impacts of load shedding on query-result accuracy. Experimental results show that LIRA is vastly superior to random update dropping and clearly outperforms other alternatives that do not possess region-aware load-shedding capabilities. Moreover, due to its lightweight nature, LIRA introduces very little overhead.