Abstract not found

User-perceived latency is recognized as the central performance problem in the Web. We systematically measure factors contributing to this latency, across several locations. Our study reveals that DNS query times, TCP connection establishment, and start-of-session delays at HTTP servers, more so than transmission time, are major causes of long waits. Wait due to these factors also afflicts high-bandwidth users and has detrimental effect on perceived performance.

Abstract-- The central performance problem in the World Wide Web, in recent years, is user perceived latency. This is the time spent by a user while waiting for a Web page he/she requested. Impatience with poor performance is the most common reason visitors terminate their visit at Web sites. For e-commerce sites, such abandonment translates into lost revenue. For this reason, measuring the delay experienced by its customers is of high importance to a Web site. These measurements are critical for analyzing the site behavior and to size its components. As of today the main tool for conducting such measurements are external, client-side tools, whereby agents located on the net request pages from the site and measure its latency. In this paper we propose a novel solution that conducts the measurements of the user perceived delay at the Web site. The major advantage of this measurement approach, as opposed to client side approach, is that is can evaluate the latency experienced by each and every client (regardless of its network location). Further, this estimate can be conducted at real time, thus allowing the server to control its operation and prioritize the requests based on the actual performance observed by the clients. The solution does not require any agents to be placed at the net. Further, it does not sniff low-level protocols (that is, IP protocols) and is all based on implementation at the HTTP level. As such, it is very efficient and economical. The solution is based on a novel technique in which a special tiny HTTP object, called the sentry, assists in measuring the user perceived latency. The algorithm is implemented on the Apache server. The implementation was tested throughout an extensive array of tests and found to provide very accurate measures.

This paper presents a introduction to the concept of persistent authenticated dictionaries. It describes the design of two such dictionaries, one based on red-black trees, and one based on skip lists. Finally, it presents measurements of an implementation of persistent authenticated skip lists compared to ephemeral (non-persistent) skip lists and red-black trees