Abstract
The dramatic growth of the Internet and of the Web traffic calls for scalable solutions to accessing Web documents. To this purpose, various caching schemes have been proposed and caching has been widely deployed. Since most Web documents change very rarely, the issue of consistency, i.e. how to assure access to the most recent version of a Web document, has received not much attention. However, as the number of frequently changing documents and the number of users accessing these documents increases, it becomes mandatory to propose scalable techniques that assure consistency. We look at one class of techniques that achieve consistency by performing automated delivery of Web documents. Among all schemes imaginable, automated delivery guarantees the lowest access latency for the clients. We compare pull- and push-based schemes for automated delivery and evaluate their performance analytically and via trace-driven simulation. We show that for both, pull- and push-based schemes, the use of a caching infrastructure is important to achieve scalability. For most documents in the Web, a pull distribution with a caching infrastructure can efficiently implement an automated delivery. However, when servers update their documents randomly and servers cannot ensure a minimum time-to-live interval during which documents remain unchanged, pull generates many requests to the origin server. For this case, we consider push-based schemes that use a caching infrastructure and we present a simple algorithm to determine which documents should be pushed given a limited available bandwidth.