With the explosive use of Internet, contemporary web servers are susceptible to overloads and their services deteriorate drastically and often cause denial of services. In this paper, we proposed two methods to prevent and control overloads in web servers by utilizing session-based relationship among HTTP requests. We first exploited the dependence among session-based requests by analyzing and predicting the reference patterns. Using the dependency relationships, wehave derived traffic conformation functions that can be used for capacity planning and overload prevention in web servers. Second, we have proposed a dynamic weighted fairing sharing (DWFS) scheduling algorithm to control overloads in web servers. DWFS is distinguished from other scheduling algorithms in the sense that it aims to avoid processing of requests that belong to sessions that are likely to be aborted in the near future. The experimental results demonstrate that DWFS can improve server responsiveness by as high as 50% while providing QoS support through service differentiation for a class of application environment.

The architecture of World Wide Web (WWW) browsers and servers support full file transfer for document retrieval. TCP is used for data transfers by Web browsers and their associated Hypertext Transfer Protocol (HTTP) servers. Full file transfer and TCP are unsuitable for continuous media, such as real time audio and video. In order for the WWW to support continuous media, we require the transmission of video and audio on-demand and in real time, as well as new protocols for real time data. We extend the architecture of the WWW to encompass the dynamic, real time information space of video and audio. Our WWW browser Vosaic, short for Video Mosaic, incorporates real time video and audio into standard hypertext pages and which are displayed in place. Video and audio transfers occur in real time; there is no file retrieval latency. The video and audio result in compelling Web pages. Real time video and audio data can be effectively served over the present day Internet with the proper transm...

Web server performance has steadily improved since the inception of the World Wide Web. We observe performance gains of two orders of magnitude between the original process-based Web servers and today's threaded Web servers. Commercial and academic Web servers achieved much of these gains using new or improved event-notification mechanisms and techniques to eliminate reading and copying data, both of which required new operating system primitives. More recently, experimental and production Web servers began integrating HTTP processing in the TCP/IP stack and providing zero copy access to a kernel-managed cache. These kernelmode Web servers improved upon newer user-mode Web servers by a factor of two to six.

This paper evaluates techniques for improving operating system and network protocol software support for high-performance WWW servers. We study approaches in 3 categories: new socket functions, per-byte optimizations, and per-connection optimizations. We examine two proposed socket functions, acceptex()and send file(), comparing send file()'s effectiveness with a combination of mmap() and writev(). We show how send file()provides the necessary semantic support to eliminate copies and checksums in the kernel, and quantify the benefit of the function's header and close options. We also present mechanisms to reduce the number of packets exchanged in an HTTP transaction, both increasing server performance and reducing network utilization, without compromising interoperability. Results using WebStone show that our combination of mechanisms can improve server throughput by up to 64 percent, and can eliminate up to 33 percent of the packets in an HTTP exchange. Results with SURGE show an aggregate increase in server throughput of 25 percent.

Abstract not found

As the World Wide Web experiences increasing commercial and mission-critical use, server systems are expected to deliver high and predictable performance. The phenomenal improvement in microprocessor speeds, coupled with the deployment of clusters of commodity workstations has enabled server systems to meet the continually increasing performance demands in a cost-effective and scalable manner. However, as the volume, variety and sophistication of services oered by server systems increase, eective support for providing dierentiated and predictable quality of service has also become important. For example, it is often desirable to dierentiate between the resources allocated to virtual web sites hosted on a server system so as to provide predictable performance to individual sites, regardless of the load imposed upon others. Server systems lack adequate support for providing predictable performance to hosted services in terms of metrics that are meaningful to server applications, such...

... In this paper, we describe the design and implementation of a QoS-enabled web server called the Web2K server. The Web2K server enables web site operators to optimize the usage of their web sites by prioritizing among requests from different classes of users. Under overload conditions, predictive queue controllers incorporated in the Web2K server enable it to selectively deny service to some percentage of requests based on the associated user classification. Unlike current web servers, the Web2K server also maintains stable response times under overload using a novel, traffic-aware request processing model

We propose a new webserver architecture optimized for delivery of large, popular files. Delivery of such files currently pose a scalability problem for conventional content providers, which must devote server-side resources in direct proportion to the high multiprogramming level induced by a set of these connections. While use of scalable multicast may remedy this problem some day, multicast is rarely supported in today's wide-area infrastructure. Our approach alleviates many of the most serious scalability problems by developing new server-side mechanisms capable of managing a large set of TCP connections transporting the same content. The strategy we employ relies on the use of fast forward error correcting (FEC) codes to generate encodings of popular content, of which only a small sliding window is cached in memory at any time instant. The concurrent TCP connections then access content only from this shared window, which is globally useful to all clients. Our method hinges on eliminating unscalable TCP retransmission buffers, as we can "retransmit" fresh encoding packets in lieu of the originals with no performance degradation and with no modifications to client TCP stacks. Ultimately, our Cyclone server capitalizes on concurrency to maximize sharing of state across different request threads while minimizing context switching, thrashing under high load and the cache memory footprint. In this paper, we describe the design and prototype implementation of our approach as a Linux kernel subsystem. Keywords: TCP, FEC, webserver, popularity, concurrency, digital fountain, Tornado codes I.

We argue that existing OS designs are ill-suited for the needs of Internet service applications. These applications demand massive concurrency (supporting a large number of requests per second) and must be well-conditioned to load (avoiding degradation of performance and predictability when demand exceeds capacity). The transparency and virtualization provided by existing operating systems leads to limited concurrency and lack of control over resource usage. We claim that Internet services would be far better supported by operating systems by reconsidering the role of resource virtualization. We propose a new design for server applications, the staged event-driven architecture (SEDA). In SEDA, applications are constructed as a set of eventdriven stages separated by queues. We present the SEDA architecture and its consequences for operating system design. 1.

An Architecture for Highly Concurrent, Well-Conditioned Internet Services by Matthew David Welsh Doctor of Philosophy in Computer Science University of California at Berkeley Professor David Culler, Chair This dissertation presents an architecture for handling the massive concurrency and load conditioning demands of busy Internet services. Our thesis is that existing programming models and operating system structures do not adequately meet the needs of complex, dynamic Internet servers, which must support extreme concurrency (on the order of tens of thousands of client connections) and experience load spikes that are orders of magnitude greater than the average. We propose a new software framework, called the staged event-driven architecture (or SEDA), in which applications are constructed as a network of event-driven stages connected with explicit queues. In this model, each stage embodies a robust, reusable software component that performs a subset of request processing. By performing admission control on each event queue, the service can be well-conditioned to load, preventing resources from being overcommitted when demand exceeds service capacity. SEDA employs dynamic control to tune runtime parameters (such as the scheduling parameters of each stage) automatically, as well as to manage load, for example, by performing adaptive load shedding.