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TailCut: Power Reduction under Quality and Latency Constraints in Distributed Search Systems
Chih-Hsun Chou, Laxmi Bhuyan and Shaolei Ren
University of California, Riverside, University of California, Riverside, University of California, Riverside

Web search constitutes an important class of dataintensive online services in data centers. Optimizing search systems for energy efficiency, timely response and high search quality (i.e., how relevant the returned results are to a search query), however, is very challenging, as a search system involves a distributed architecture with hundreds of thousands of index serving nodes (ISNs) that return searching results to an aggregator through multiple interdependent retrieval stages in a partition-aggregate fashion. In this paper, we discover through experiments two important characteristics that can affect the system performance: (1) response time and energy consumption are greatly impacted by a small fraction of queries with long processing times; (2) the quality contribution of the ISN is independent of the query processing time. Based on our observation, we propose TailCut, which judiciously discards long query executions and enables ISN-aggregator coordination to minimize energy consumption subject to latency and quality constraints. Our experimental results show that TailCut can achieve up to 39% power saving, while satisfying the tail latency and quality constraint.