Measuring consistency in TTL-based caches
Performance Evaluation - Performance 2005
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Abstract: Wireless devices currently provide real-time access to personalized information such as headlines, email, stock quotes, and on-line auctions. Retrieving all updates to such rapidly changing information is wasteful of both network bandwidth and battery power. Existing consistency models for such services allow for only coarse-grained timeouts on how often information should be retrieved. In this paper, we argue for the benefits of a continuous consistency model for user access to Internet portal services. Using this model, users are able to specify the maximum error in their view of the data. For instance, users may specify that they wish to receive an updated stock quote only if the users view diverges from the actual value by more than 3%. Services may also use application-specific semantics to control data consistency- e.g., new bids carry more weight as the auction draws to a close. We use a simulator to model the bandwidth and energy benefits available from a more flexible consistency model. Such benefits depend upon the rate at which underlying data values change. To capture representative distributions, we use a trace-based study of updates to weather, news, and stock quotes from a popular portal to determine representative distribution ranges. Our initial results indicate bandwidth and energy savings that increase as users are willing to tolerate larger bounds on data accuracy.