Web caching is an important technique to scale the Internet. One important performance factor of Web caches is the replacement strategy. Due to specific characteristics of the World Wide Web, there exist a huge number of proposals for cache replacement. This article proposes a classification for these proposals that subsumes prior classifications. Using this classification, different proposals and their advantages and disadvantages are described. Furthermore, the article discusses the importance of cache replacement strategies in modern proxy caches and outlines potential future research topics.

/pdf/a-survey-of-web-cache-replacement-strategies-1h4qa1pui3.pdf

A survey of Web cache replacement strategies

Workload generators may be classified as based on a closed system model, where new job arrivals are only triggered by job completions (followed by think time), or an open system model, where new jobs arrive independently of job completions. In general, system designers pay little attention to whether a workload generator is closed or open.

Using a combination of implementation and simulation experiments, we illustrate that there is a vast difference in behavior between open and closed models in real-world settings. We synthesize these differences into eight simple guiding principles, which serve three purposes. First, the principles specify how scheduling policies are impacted by closed and open models, and explain the differences in user level performance. Second, the principles motivate the use of partly open system models, whose behavior we show to lie between that of closed and open models. Finally, the principles provide guidelines to system designers for determining which system model is most appropriate for a given workload.

/pdf/open-versus-closed-a-cautionary-tale-46c85teo8d.pdf

Open versus closed: a cautionary tale

Policy-based management provides a means for IT systems to operate according to business needs. Unfortunately, there is often an "impedance mismatch" between the policies administrators want and the controls they are given. Consider the Apache Web server. Administrators want to control CPU and memory utilizations, but this must be done indirectly by manipulating tuning parameters such as MaxClients and KeepAlive. There has been much interest in using feedback control to bridge the impedance mismatch. However, these efforts have focused on a single metric that is manipulated by a single control and hence have not considered interactions between controls such as those that are common in computing systems. This paper shows how multiple-input, multiple-output (MIMO) control theory can be used to enforce policies for interrelated metrics. MIMO is used both to model the target system, Apache in our case, and to design feedback controllers. The MIMO model captures the interactions between KA and MC, and can be used to identify infeasible metric policies. In addition, MIMO control techniques can provide considerable benefit in handling trade-offs between speed of metric convergence and sensitivity to random fluctuations while enforcing the desired policies.

https://cs.uwaterloo.ca/~brecht/servers/readings-new/noms2002_MIMO.pdf

Using MIMO feedback control to enforce policies for interrelated metrics with application to the Apache Web server

We present a methodology for maximizing profits in a general class of e-commerce environments. The cost model is based on revenues that are generated when Quality-of-Service (QoS) guarantees are satisfied and on penalties that are incurred otherwise. The corresponding QoS criteria are derived from multiclass Service-Level-Agreements (SLAs) between service providers and their clients, which include the tail distributions of the per-class delays in addition to more standard QoS metrics such as throughput and mean delays. Our approach consists of formulating the optimization problem as a network flow model with a separable set of concave objective functions based on queueing-theoretic formulas, where the SLA classes are taken into account in both the constraints and the objective function. This problem is then solved via a fixed-point iteration. Numerous experiments illustrate the benefits of our approach.

On maximizing service-level-agreement profits

Gives constant approximations for a number of layered network design problems. We begin by modeling hierarchical caching, where the caches are placed in layers and each layer satisfies a fixed percentage of the demand (bounded miss rates). We present a constant approximation to the minimum total cost of placing the caches and to the routing demand through the layers. We extend this model to cover more general layered caching scenarios, giving a constant combinatorial approximation to the well-studied multi-level facility location problem. We consider a facility location variant, the load-balanced facility location problem, in which every demand is served by a unique facility and each open facility must serve at least a certain amount of demand. By combining load-balanced facility location with our results on hierarchical caching, we give a constant approximation for the access network design problem.

/pdf/hierarchical-placement-and-network-design-problems-4msl2natim.pdf

Hierarchical placement and network design problems

Almost ten years after its premises, the Grid’5000 testbed has become one of the most complete testbed for designing or evaluating large-scale distributed systems. Initially dedicated to the study of High Performance Computing, the infrastructure has evolved to address wider concerns related to Desktop Computing, the Internet of Services and more recently the Cloud Computing paradigm. This paper present recent improvements of the Grid’5000 software and services stack to support large-scale experiments using virtualization technologies as building blocks. Such contributions include the deployment of customized software environments, the reservation of dedicated network domain and the possibility to isolate them from the others, and the automation of experiments with a REST API. We illustrate the interest of these contributions by describing three different use-cases of large-scale experiments on the Grid’5000 testbed. The first one leverages virtual machines to conduct larger experiments spread over 4000 peers. The second one describes the deployment of 10000 KVM instances over 4 Grid’5000 sites. Finally, the last use case introduces a one-click deployment tool to easily deploy major IaaS solutions. The conclusion highlights some important challenges of Grid’5000 related to the use of OpenFlow and to the management of applications dealing with tremendous amount of data.

Adding Virtualization Capabilities to the Grid’5000 Testbed

https://hal.inria.fr/inria-00072817/document

Traffic model and performance evaluation of Web servers

With the increasing popularity of the World Wide Web, the amount of information available and the use of Web servers are growing exponentially. As a consequence, the number of requests to popular Web servers increases exponentially as well. In order to reduce the overhead induced by frequent requests to the same documents, server caching, also referred to as main memory caching, has been proposed and implemented. In this work, we propose a static caching mechanism which consists of updating the contents of the cache periodically and, at the update time, brings into the cache only the most requested documents in the previous time interval. This caching policy has lower management overhead than others. Under some statistical assumptions we show that static caching has the highest hit rate. We also provide empirical comparison results obtained by trace-driven simulations. It turns out that static caching is more efficient in terms of hit rate than those analyzed in the literature.

Static caching of Web servers

Almost ten years after its premises, the Grid'5000 testbed has become one of the most complete testbed for designing or evaluating large-scale distributed systems. Initially dedicated to the study of High Performance Computing, the infrastructure has evolved to address wider concerns related to Desktop Computing, the Internet of Services and more recently the Cloud Computing paradigm. This report present recent improvements of the Grid'5000 software and services stack to support large-scale experiments using virtualization technologies as building blocks. Such contributions include the deployment of customized software environments, the reservation of dedicated network domain and the possibility to isolate them from the others, and the automation of experiments with a REST API. We illustrate the interest of these contributions by describing three different use-cases of large-scale experiments on the Grid'5000 testbed. The first one leverages virtual machines to conduct larger experiments spread over 4000 peers. The second one describes the deployment of 10000 KVM instances over 4 Grid'5000 sites. Finally, the last use case introduces a one-click deployment tool to easily deploy major IaaS solutions. The conclusion highlights some important challenges of Grid'5000 related to the use of OpenFlow and to the management of applications dealing with tremendous amount of data.

https://hal.inria.fr/hal-00720910/document

Nicolas Niclausse

Papers

Adding Virtualization Capabilities to the Grid’5000 Testbed

Traffic model and performance evaluation of Web servers

Static caching of Web servers

Adding Virtualization Capabilities to Grid'5000

Web traffic modeling and performance comparison between HTTP1.0 and HTTP1.1