Exploiting regularities in web traffic patterns for cache replacement

Caching web pages at proxies and in web servers' memories can greatly enhance performance. Proxy caching is known to reduce network load and both proxy and server caching can significantly decrease latency. Web caching problems have different properties than traditional operating systems paging, and cache replacement can benefit by recognizing and exploiting these differences. We address two aspects of the predictability of traffic patterns: the overall load experienced by large proxy and web servers, and the distinct access patterns of individual pages. We formalize the notion of `cache load' under various replacement policies, including LRU and LFU, and demonstrate that the trace of a large proxy server exhibits regular load. Predictable load allows for improved design, analysis, and experimental evaluation of replacement policies. We provide a simple and (near)-optimal replacement policy when each page request has an associated distribution function on the next request time for the page. Without the predictable load assumption, no such online policy is possible and it is known that even obtaining an offline optimum is hard. For experiments, predictable load enables comparing and evaluating cache replacement policies using partial traces, containing requests made to only a subset of the pages. Our results are based on considering a simpler interval caching model for cache replacement. We relate traditional and interval-caching policies under predictable load, and derive (near)-optimal replacement policies from their optimal interval-caching counterparts.