Modeling and Anallysis of An Expiration-Based Hierarchical Caching System

Absmcr- Caching is an important m- to wale up the invalidation [5]) is that they often involve higher overhead and growth of the lotemet. Weak consistency is a mdor approach complexity and are expensive to deploy. Nevertheless, strong used in caching and has in forms. consistency is an indispensable approach to deliver mission This paper investigates some properties and performance issues of an apirstion-hased system. we on a critical contents on the Web. On the other hand. under weak & system h & on the %e-~o.fiw (m) =piration consistency, it is allowed to let a user get a somewhat stale ob-mechanism and present a basic model for such U system. By an. ject from the cache server. The cache server only validates the dyzing the intrinsic T1z timing behavior in the basic model, we object’s freshness with the origin server periodically and may derive the I p e r s p lag behind the actual update at the origin server. Weak consis-tency is particularly useful for those web contents that can tol- tive ofthe caching system and end users, respectively. Our results oller some basic understanding of a hierarchical caching system based on the weak consistency paradigm erate a certain degree of discrepancy between cached content and the content at origin server as long as it is understood that such discrepancy in time does not cause any harm. It is impor-tant to keep such discrepancy not to exceed a reasonable pe-nod of time. Example applications using weak consistency in