The Internet is undergoing substantial changes from a communication and browsing infrastructure to a medium for conducting business and marketing a myriad of services. The World Wide Web provides a uniform and widely-accepted application interface used by these services to reach multitudes of clients. These changes place the web server at the center of a gradually emerging eservice infrastructure with increasing requirements for service quality and reliability guarantees in an unpredictable and highly-dynamic environment.

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This paper presents a method for admission control and request scheduling for multiply-tiered e-commerce Web sites, achieving both stable behavior during overload and improved response times. Our method externally observes execution costs of requests online, distinguishing different request types, and performs overload protection and preferential scheduling using relatively simple measurements and a straightforward control mechanism. Unlike previous proposals, which require extensive changes to the server or operating system, our method requires no modifications to the host O.S., Web server, application server or database. Since our method is external, it can be implemented in a proxy. We present such an implementation, called Gatekeeper, using it with standard software components on the Linux operating system. We evaluate the proxy using the industry standard TPC-W workload generator in a typical three-tiered e-commerce environment. We show consistent performance during overload and throughput increases of up to 10 percent. Response time improves by up to a factor of 14, with only a 15 percent penalty to large jobs.

The ability of a web service to provide low-latency access to its contents is constrained by available network bandwidth. It is important for the service to manage available bandwidth wisely. While providing differentiated quality of service (QoS) is typically enforced through network mechanisms, in this paper we introduce a robust mechanism for managing network resources at the application level. We use transcoding to allow web servers to customize the size of objects constituting a web page, and hence the bandwidth consumed by that page, by dynamically varying the size of multimedia objects on a per-client basis. We leverage earlier work on characterizing quality versus size tradeoffs in transcoding JPEG images to dynamically determine the quality and size of the object to transmit. We evaluate the performance benefits of incorporating this information in a series of bandwidth management policies. We develop metrics to measure the performance of our system. We use realistic workloads...

* The current World-Wide Web service model treats all requests equivalently, both while being processed by servers and while being transmitted over the network. For some uses, such as web prefetching or multiple priority schemes, different levels of service are desirable. This paper presents three simple, server-side, application -level mechanisms (limiting process pool size, lowering process priorities, limiting transmission rate) to provide two different levels of web service (regular and low priority). We evaluated the performance of these mechanisms under combinations of two foreground workloads (light and heavy) and two levels of available network bandwidth (10Mb/s and 100Mb/s). Our experiments show that even with background traffic sufficient to saturate the network, foreground performance is reduced by at most 4-17%. Thus, our user-level mechanisms can effectively provide different service classes even in the absence of operating system and network support. 1. Introduction The ...

With the dramatic explosion of online information, the Internet is undergoing a transition from a data communication infrastructure to a global information utility . PDAs, wireless phones, webenabled vehicles, modem PCs and high-end workstations can be viewed as appliances that "plug-in" to this utility for information. The increasing diversity of such appliances calls for an architecture for performance differentiation of information access. The World Wide Web is the dominant interface to the information utility today. Web proxy caching is the key performance accelerator in the web infrastructure. Client-perceived performance of Internet information access depends in great part on the local cache proxy performance. While many research efforts addressed performance differentiation in the network, providing multiple levels of service in proxy caches has received much less attention. This paper has two main contributions. First, we describe, implement, and evaluate an architecture for d...

We have implemented these mechanisms in AIX 5.0. Through numerous experiments we demonstrate their effectiveness in achieving the desired degree of service differentiation during overload. We also show that the kernel mechanisms are more efficient and scalable than application level controls implemented in the Web server.

Service differentiation that provides prioritized service qualities to multiple classes of client requests can effectively utilize available server resources. This paper studies how demand-driven service differentiation in terms of end-user performance can be supported in cluster-based network servers. Our objective is to deliver better services to high priority request classes without over-sacrificing low priority classes. To achieve this objective, we propose a dynamic scheduling scheme, called DDSD, that adapts to fluctuating request resource demands by periodically repartitioning servers. This scheme also employs priority-based admission control to drop excessive user requests and achieve soft performance guarantees. For each scheduling period, our scheme monitors the system status and uses a queuing model to approximate server behaviors and guide resource allocation. Our experiments show that the proposed technique achieves demand-driven service differentiation while maximizing resource utilization and that it can substantially outperform static server partitioning.

The paper describes modeling and performance control of an Internet server using classical feedback control theory. We show that classical feedback control can leverage on well-known real-time scheduling results to resolve one of the fundamental problems in Internetservers today; namely, achieving overload protection and performance guarantees in the presence of load unpredictability. The research is motivated by the increasing proliferation of a new category of Web-based services, such as online trading, banking, and business transactions, where performance guarantees are required in the face of unpredictable server load. Failure to meet desired performance levels may result in loss of customers, financial damage or liability violations. State-of-the-art Web servers are not designed to offer such performance guarantees. We show that control theory offers a robust solution to the server performance control problem. We demonstrate that a general web server may be modeled as a linear ti...

As businesses continue to grow their World Wide Web presence, it is becoming increasingly vital for them to have quantitative measures of the client perceived response times of their web services. We present Certes (CliEnt Response Time Estimated by the Server), an online server-based mechanism for web servers to measure client perceived response time, as if measured at the client. Certes is based on a model of TCP that quantifies the e#ect that connection drops have on perceived client response time, by using three simple server-side measurements: connection drop rate, connection accept rate and connection completion rate. The mechanism does not require modifications to http servers or web pages, does not rely on probing or third party sampling, and does not require client-side modifications or scripting. Certes can be used to measure response times for any web content, not just HTML. We have implemented Certes and compared its response time measurements with those obtained with detailed client instrumentation. Our results demonstrate that Certes provides accurate server-based measurements of client response times in HTTP 1.0/1.1 [14] environments, even with rapidly changing workloads. Certes runs online in constant time with very low overhead. It can be used at web sites and server farms to verify compliance with service level objectives.