Aging through cascaded caches: performance issues in the distribution of web content
Proceedings of the 2001 conference on Applications, technologies, architectures, and protocols for computer communications
DNS performance and the effectiveness of caching
IMW '01 Proceedings of the 1st ACM SIGCOMM Workshop on Internet Measurement
The age penalty and its effect on cache performance
USITS'01 Proceedings of the 3rd conference on USENIX Symposium on Internet Technologies and Systems - Volume 3
| Hi-index | 0.00 |
The web is the largest distributed database deploying time-to-live-based weak consistency. Each object has a lifetime-duration assigned to it by its origin server. A copy of the object fetched from its origin server is received with maximum time-to-live (TTL) that equals its lifetime duration. In contrast a copy obtained through a cache have shorter TTL since the age (elapsed time since fetched from the origin) is deducted from its lifetime duration. A request served by a cache constitutes a hit if the cache has a fresh copy of the object. Otherwise, the request is considered a miss and is propagated to another server. It is evident that the number of cache misses depends on the age of the copies the cache receives. Thus, a cache that sends requests to another cache would suffer more misses than a cache that sends requests directly to an authoritative server.In this paper, we model and analyze the effect of age on the performance of various cache configurations. We consider a low-level cache that fetches objects either from their origin servers or from other caches and analyze its miss-rate as function of its fetching policy. We distinguish between three basic fetching policies, namely, fetching always from the origin, fetching always from the same high-level cache, and fetching from a "random" high-level cache. We explore the relationships between these policies in terms of the miss-rate achieved by the low-level cache, both on worst-case sequences, and on sequences generated using particular probability distributions.Guided by web caching practice, we consider two variations of the basic policies. In the first variation the high-level cache uses pre-term refreshes to keep a copy with lower age. In the second variation the low-level cache uses extended lifetime duration. We analyze how these variations affect the miss-rates. Our theoretical results help to understand how age may affect the miss-rate, and imply guidelines for improving performance of web caches.