NCSA is adding support for group and public annotations to its HTTP server and Mosaic client. The primary concern addressed in this paper is how to ensure that the feature is scalable. Our solution requires each document server to tell the client where to get public annotations for a document, whereas the user tells the client where to get group annotations for a document. We argue that our solution is no less scalable than the web itself. Finally, we address the problem of finding out what is new.
James Gwertzman, Microsoft Corporation, Margo Seltzer, Harvard University
The bandwidth demands of the World Wide Web continue to grow at a hyper-exponential rate. Given this rocketing growth, caching of web objects as a means to reduce network bandwidth consumption is likely to be a necessity in the very near future. Unfortunately, many Web caches do not satisfactorily maintain cache consistency. This paper presents a survey of contemporary cache consistency mechanisms in use on the Internet today and examines recent research in Web cache consistency. Using trace-driven simulation, we show that a weak cache consistency protocol (the one used in the Alex ftp cache) reduces network bandwidth consumption and server load more than either time-to-live fields or an invalidation protocol and can be tuned to return stale data less than 5% of the time.