Speculative validation of web objects for further reducing the user-perceived latency

Abstract

Web caching techniques reduce user-perceived latency by serving the most popular web objects from an intermediate memory. In order to assure that reused objects are not stale, conditional requests are sent to the origin web servers before serving them. Most of the server responses to the conditional requests ratify that the object remains valid and, as a consequence, they do not include the object itself. Therefore, the object transfer time is completely saved when the object is still valid. However, the round-trip time (RTT) of these short responses cannot be saved. This time represents an important fraction of the response time in the current Internet scenario and makes conditional requests save less perceived latency than when they were proposed. This paper proposes an approach to reduce the amount of conditional requests needed to maintain web cache consistency, thus completely saving both mentioned times (transfer and RTT) taken by such requests. To this end, our system uses a speculative approach similar to the one used in web prefetching which pre-sends freshness labels instead of web objects. The proposed technique has been evaluated using current and representative web traces. Experimental results show that the proposal dramatically reduces up to 55% of both the user-perceived latency and the amount of requests that the server receives. © 2010 Springer-Verlag.