Web Server Performance in a WAN Environment

Abstract—This work analyzes web server performance under simulated WAN conditions. The workload simulates many critical network characteristics, such as network delay, bandwidth limit for client connections, and small MTU sizes to dial-up clients. A novel aspect of this study is the examination of the internal behavior of the web server at the network protocol stack and the device driver. Many known server design optimizations for performance improvement were evaluated in this simulated environment. We discovered that WAN network characteristics may significantly change the behavior of the web server compared to the LAN-based simulations and make many of optimizations of the server design irrelevant in this environment. Particularly, we found out that small MTU size of the dial-up user connections can increase the processing overhead several times. At the same time, the network delay, connection bandwidth limit, and usage of HTTP/1.1 persistent connections do not have a significant effect on the server performance. We have found there is little benefit due to copy and checksum avoidance, optimization of request concurrency management, and connection open/close avoidance under a workload with small MTU sizes, which is common for dial-up users. I

Document replication and distribution in extensible geographically distributed web servers

A geographically distributed web server (GDWS) system consists of multiple server nodes interconnected by a metropolitan area network (MAN) or a wide area network (WAN). It can achieve better efficiency in handling ever-increasing web requests than centralized web servers because its throughput will not be limited by available bandwidth connecting to a central server. The key research issue in the design of GDWS is how to replicate and distribute the documents of a website among the server nodes. This paper proposes a density-based replication scheme and applies it to our proposed Extensible GDWS architecture. We adopted a partial duplication scheme where document replication targets only at hot objects in a website. To distribute the replicas generated via the density-based replication scheme, we propose four different document distribution algorithms: Greedy-cost, Maximal-density, Greedy-penalty, and Proximity-aware. A proximity-based routing mechanism is designed to incorporate these algorithms for achieving better web server performance in a WAN environment. Simulation results show that the Greedy-penalty algorithm yields most stable load-balancing performance, and the Greedy-cost algorithm causes least internal traffic. Our scheme can achieve 80% of the performance of full-replication, with half the disk space. © 2003 Elsevier Inc. All rights reserved.link_to_subscribed_fulltex

Document Replication and Distribution in Extensible Geographically Distributed Web Servers

A geographically distributed web server (GDWS) system consists of multiple server nodes interconnected by a metropolitan area network (MAN) or a wide area network (WAN). It can achieve better eciency in handling ever-increasing web requests than centralized web servers because its throughput will not be limited by available bandwidth connecting to a central server. The key research issue in the design of GDWS is how to replicate and distribute the documents of a website among the server nodes. This paper proposes a density-based replication scheme and applies it to our proposed Extensible GDWS architecture. We adopted a partial duplication scheme where document replication targets only at hot objects in a website. To distribute the replicas generated via the density-based replication scheme, we propose four dierent document distribution algorithms: Greedy-cost, Maximal-density, Greedy-penalty, and Proximity-aware. A proximity-based routing mechanism is designed to incorporate these algorithms for achieving better web server performance in a WAN environment. Simulation results show that the Greedy-penalty algorithm yields most stable load balancing performance, and the Greedy-cost algorithm causes least internal trac. Our scheme can achieve80%of the performance of full-replication, with half the disk space. Key words: Document replication and distribution, Distributed web server