Due to the tremendous cooling costs, data center cooling efficiency improvement has been actively pursued for years. In addition to cooling efficiency, the reliability of the cooling system is also essential for guaranteed uptime. In traditional data center cooling system design with N+1 or higher redundancy, all the computer room air conditioning (CRAC) units are either constantly online or cycled according to a predefined schedule. Both cooling system configurations, however, have their respective drawbacks. Data centers are usually over provisioned when all CRAC units are online all the time, and hence the cooling efficiency is low. On the other hand, although cooling efficiency can be improved by cycling CRAC units and turning off the backups, it is difficult to schedule the cycling such that sufficient cooling provisioning is guaranteed and gross over provisioning is avoided. In this paper, we aim to maintain the data center cooling redundancy while achieving high cooling efficiency. Using model- based thermal zone mapping, we first partition data centers to achieve the desired level of cooling redundancy through zone overlap adjustment. We then design a distributed controller for each of the CRAC units to regulate the thermal status within its zone of influence. The distributed controllers coordinate with each other to achieve the desired data center thermal status using the least cooling power. When CRAC units or their associated controllers fail, racks in the affected thermal zones are still within the control "radius" of other decentralized cooling controllers through predefined thermal zone overlap, and hence their thermal status is properly managed by the active CRAC units and controllers. Using this failure resistant data center cooling control approach, both cooling efficiency and robustness are achieved simultaneously. A higher flexibility in cooling system maintenance is also expected, since the distributed control system can automatically adapt to the new cooling facility configuration incurred by maintenance.

关键词：数据中心；冷却；热区

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The World Wide Web and the services it provides are continually evolving. Even for a single time instant, it is a complex task to methodologically determine the infrastructure over which these services are provided and the corresponding effect on user perceived performance. For such tasks, researchers typically rely on active measurements or large numbers of volunteer users. In this paper, we consider an alternative approach, which we refer to as passive crowd-based monitoring. More specifically, we use passively collected proxy logs from a global enterprise to observe differences in the quality of service (QoS) different Web content providers. While some of these properties have been observed using active measurements, we are the first to show that many of these properties (such as location of servers) can be obtained using passive measurements of actual user activity. Passive crowd-based monitoring has the advantages that it does not add any overhead on Web infrastructure, it does not require any specific software on the clients, but still captures the performance and infrastructure observed by actual Web usage.

关键词：万维网；被动监控；以人群为基础的监测

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Reduction of resource consumption in data centers is becoming a growing concern for data center designers, operators and users. Accordingly, interest in the use of renewable energy to provide some portion of a data center's overall energy usage is also growing. One key concern is that the amount of renewable energy necessary to satisfy a typical data center's power consumption can lead to prohibitively high capital costs for the power generation and delivery infrastructure, particularly if on-site renewables are used. In this paper, we introduce a method to operate a data center with renewable energy that minimizes dependence on grid power while minimizing capital cost. We achieve this by integrating data center demand with the availability of resource supplies during operation. We discuss results from the deployment of our method in a production data center.

关键词：数据中心；净零能源；可再生能源；可持续发展

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Cloud computing refers to the underlying infrastructure for an emerging model of service provision that has the advantage of reducing cost by sharing computing and storage resources, combined with an on-demand provisioning mechanism relying on a pay- per-use business model. These new features have a direct impact on information technology (IT) budgeting but also affect traditional security, trust and privacy mechanisms. The advantages of cloud computing - its ability to scale rapidly, store data remotely, and share services in a dynamic environment - can become disadvantages in maintaining a level of assurance sufficient to sustain confidence in potential customers. Some core traditional mechanisms for addressing privacy (such as model contracts) are no longer flexible or dynamic enough, so new approaches need to be developed to fit this new paradigm. In this chapter we assess how security, trust and privacy issues occur in the context of cloud computing and discuss ways in which they may be addressed.

关键词：云计算；隐私；安全；信任

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This paper examines historical releases of Sendmail, Postfix, Apache httpd and OpenSSL by using static source code analysis and the entry-rate in the Common Vulnerabilities and Exposures dictionary (CVE) for a release, which we take as a measure of the rate of discovery of exploitable bugs. We show that the change in number and density of issues reported by the source code analyzer is indicative of the change in rate of discovery of exploitable bugs for new releases - formally we demonstrate a statistically significant correlation of moderate strength. The strength of the correlation is an artifact of other factors such as the degree of scrutiny: the number of security analysts investigating the software. This also demonstrates that static source code analysis can be used to make some assessment of risk even when constraints do not permit human review of the issues identified by the analysis. We find only a weak correlation between absolute values measured by the source code analyzer and rate of discovery of exploitable bugs, so in general it is unsafe to use absolute values of number of issues or issue densities to compare different applications or software. Our results demonstrate that software quality, as measured by the number of issues, issue density or number of exploitable bugs, does not always improve with each new release. However, generally the rate of discovery of exploitable bugs begins to drop three to five years after the initial release. Copyright ACM 2012. This is the author's version of the work. It is posted here by permission of ACM for your personal use. Not for redistribution. The definitive version was published in CCS'12, 19th ACM Conference on Computer and Communications Security, October 16 - 18, 2012, Raleigh, North Carolina, USA.

关键词：安全；防护；检测；静态分析；风险分析；开源软件

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关键词：分配问题；不完善匹配；最低成本；不平衡的二分图；重量缩放算法

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We present the results of a multi-phase study to optimize strategies for generating personalized article recommendations at the Forbes.com web site. In the first phase we compared the performance of a variety of recommendation methods on historical data. In the second phase we deployed a live system at Forbes.com for five months on a sample of 82,000 users, each randomly assigned to one of 20 methods. We analyze the live results both in terms of click- through rate (CTR) and user session lengths. The method with the best CTR was a hybrid of collaborative-filtering and a content-based method that leverages Wikipedia-based concept features, post- processed by a novel Bayesian remapping technique that we introduce. It both statistically significantly beat decayed popularity and increased CTR by 37%.

关键词：个性化；推荐系统；协同过滤；内容分析；实时用户试用

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In the IT Outsourcing industry, a complex transition and transformation process is required for on-boarding large enterprise clients. The process begins after the client signs a contract, and ends when steady-state operation is attained by the service provider. Large outsourcing deals may last several years, involve several hundred million dollars, and are traditionally highly customized to the client. In this paper, we provide recommendations for a governance framework that can manage the on-boarding stage of large, customized deals. There are no existing governance frameworks that work well at the scale and diversity observed in these deals. The framework must standardize a set of processes to direct, control, and measure on-boarding activities and enable a governance organization to create and maintain a single data, process and program management instance for each client. It must also maintain a well-defined and comprehensive view of the key entities in the transition and transformation process, and their relationships. These entities may include projects, people, roles and responsibilities, process metrics, services, and the multiple internal and partner organizations and their operational level agreements (OLAs). Finally, the framework must improve repeatability across service deals, enforce adoption of best practices that are distilled from historical deals, and better avoid known problems and issues.

关键词：治理框架；过渡和转变； IT外包

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With the introduction of cloud computing and Web 2.0, many applications are moving to the cloud environment. Version control systems have also taken a first step towards this direction. Nevertheless, existing systems are either client-server oriented or completely distributed, and they don't match exactly the nature of the cloud. In this paper we propose a new cloud version control system focusing on the requirements imposed by cloud computing, that we identified as: concurrent editing, history rewrite, accountability, scalability, security, and fault tolerance. Our plan is to tackle these issues in a systematic way, and we present in this paper an overview of the solutions organized in three separate layers: access API, logical structure, and physical storage.

关键词：软件开发；云计算；版本控制系统；修订；协作

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Web-based services are used by many organizations to support their customers and employees. An important consideration in developing such services is ensuring the Quality of Service (QoS) that users experience is acceptable. Recent years have seen a shift toward deploying Web services on multi-core hardware. Leveraging the performance benefits of multi-core hardware is a non-trivial task. In particular, systematic Web server benchmarking techniques are needed so organizations can verify their ability to meet customer QoS objectives while effectively utilizing such hardware. However, our recent experiences suggest that the multi-core era imposes significant challenges to Web server benchmarking. In particular, due to limitations of current hardware monitoring tools, we found that a large number of experiments are needed to detect complex bottlenecks that can arise in a multi-core system due to contention for shared resources such as cache hierarchy, memory controllers and processor inter-connects. Furthermore, multiple load generator instances are needed to adequately stress multi-core hardware. This leads to practical challenges in validating and managing the test results. This paper describes the automation strategies we employed to overcome these challenges. We make our test harness available for other researchers and practitioners working on similar studies.

关键词：软件性能；性能测试；多核服务器

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