document: Improved techniques for result caching in web search engines Query processing is a major cost factor in operating large web search engines . In this paper , we study query result caching , one of the main techniques used to optimize query processing performance . Our first contribution is a study of result caching as a weighted caching problem . Most previous work has focused on optimizing cache hit ratios , but given that processing costs of queries can vary very significantly we argue that total cost savings also need to be considered . We describe and evaluate several algorithms for weighted result caching , and study the impact of Zipf-based query distributions on result caching . Our second and main contribution is a new set of feature-based cache eviction policies that achieve significant improvements over all previous methods , substantially narrowing the existing performance gap to the theoretically optimal ( clairvoyant ) method . Finally , using the same approach , we also obtain performance gains for the related problem of inverted list caching .
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