Abstract

With the increasing demand for document transfer services such as the World Wide Web comes a need forbetter resource management to reduce the latency of documents in these systems. To address this need, we analyze the potential for document caching at the application level in document transfer services. We have collected traces of actual executions of Mosaic, re ecting over half a million user requests for WWW documents. Using those traces, we study the tradeo s between caching at three levels in the system, and the potential for use of application-level information in the caching system. Our traces show that while a high hit rate in terms of URLs is achievable, a much lower hit rate is possible in terms of bytes, because most pro tably-cached documents are small. We consider the performance ofcaching when applied at the level of individual user sessions, at the level of individual hosts, and at the level of a collection of hosts on a single LAN. We show that the performance gain achievable by caching at the session level (which is straightforward to implement) is nearly all of that achievable at the LAN level (where caching is more di cult to implement). However, when resource requirements are considered, LAN level caching becomes much more desirable, since itcan achieve a given level of caching performance using a much smaller amount of cache space. Finally, we consider the use of organizational boundary information as an example of the potential for use of application-level information in caching. Our results suggest that distinguishing between documents produced locally and those produced remotely can provide useful leverage in designing caching policies, because of di erences in the potential for sharing these two document types among multiple users. 1

Citations