There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Observing Interaction: An Introduction to Sequential Analysis, Roger Bakeman, John M. Gottman. Cambridge University Press, Cambridge (1986), ixv, +221. Price £25.00 hardback, £7.95 paperback

The overall increase in traffic on the World Wide Web is augmenting user-perceived response times from popular Web sites, especially in conjunction with special events. System platforms that do not replicate information content cannot provide the needed scalability to handle large traffic volumes and to match rapid and dramatic changes in the number of clients. The need to improve the performance of Web-based services has produced a variety of novel content delivery architectures. This article will focus on Web system architectures that consist of multiple server nodes distributed on a local area, with one or more mechanisms to spread client requests among the nodes. After years of continual proposals of new system solutions, routing mechanisms, and policies (the first dated back to 1994 when the NCSA Web site had to face the first million of requests per day), many problems concerning multiple server architectures for Web sites have been solved. Other issues remain to be addressed, especially at the network application layer, but the main techniques and methodologies for building scalable Web content delivery architectures placed in a single location are settled now. This article classifies and describes main mechanisms to split the traffic load among the server nodes, discussing both the alternative architectures and the load sharing policies. To this purpose, it focuses on architectures, internal routing mechanisms, and dispatching request algorithms for designing and implementing scalable Web-server systems under the control of one content provider. It identifies also some of the open research issues associated with the use of distributed systems for highly accessed Web sites.

The state of the art in locally distributed Web-server systems

A system, method and computer readable medium are disclosed for reducing power consumption in clusters, grids, on-demand centers, and so forth. The principles disclosed herein can reduce both direct and indirect power consumption while maintaining either full cluster performance or adequate SLA based cluster performance. The method includes receiving at least one state data point regarding power consumption or temperature of at least one resource within the compute environment. Using intelligent policies to control power consumption, the method implements and interfaces with power managements facilities within the cluster, grid or on-demand center to either implement policies, make dynamic changes, make predictions or actions, and so forth to reduce one or more of the direct or indirect power consumption associated with a compute environment. The method can analyze current workload, future workload or both in taking energy saving actions in the environment. An aspect can also involve reporting state information and updating algorithms based on historical experience or outside sources of information such as the news or weather.

System and method for managing energy consumption in a compute environment

Upon receipt of a document request, a client assistant examines its cache for the document. If not successful, a server searches for the requested document in its cache. If the server copy is still not fresh or not found, the server seeks the document from its host. If the host cannot provide the copy, the server seeks it from a document repository. Certain documents are identified from the document repository as being fresh or stable. Information about each these identified documents is transmitted to the server which inserts entries into an index if the index does not already contain an entry for the document. If and when this particular document is requested, the document will not be present in the server, however the server will contain an entry directing the server to obtain the document from the document repository rather than the document's web host.

System and method of accessing a document efficiently through multi-tier web caching

A system and method for maintaining consistency in a system where multiple copies of an object may exist is provided for maintaining consistent copies. Consistency is maintained using a plurality of consistency policies in which at least one consistency policy results in different performance than a second consistency policy. A consistency policy is selected from the plurality consistency policies for each object to improve system performance.

System and method for achieving different levels of data consistency

In a system having a plurality of caches, a method for maintaining cached objects includes storing an object in a plurality of caches. In response to a request to update the object, a future invalidation time is determined when the object should be invalidated in caches currently storing the object. Updating of the object is delayed until the invalidation time has passed.

System and method for achieving deferred invalidation consistency

Techniques for selectively off-loading workload across multiple data centers are disclosed. For example, a technique for processing a user request in accordance with a multiple data center environment comprises the following steps/operations. A user request is obtained at a first data center. The user request is classified based on one or more classification criterion. At least a portion of a workload associated with the classified user request is off-loaded to at least a second data center to be processed, wherein the off-loading step/operation is at least based on one or more administrative policies associated with at least one of the first data center and the second data center. The workload is processed such that the user request is at least substantially satisfied in accordance with a service level agreement for the requesting user.

Methods and apparatus for selective workload off-loading across multiple data centers

Aspects of the present invention dynamically reduce a frequency at which IT infrastructure automatically generates alerts. Historical data across a plurality of data sources in the IT infrastructure is analyzed. An opportunity to reduce the frequency at which the IT infrastructure automatically generates the alerts is identified. A new alert policy addressing the opportunity to reduce alert frequency is generated. An impact of the new alert policy on a set of predefined service level objectives (SLOs) and service level agreements (SLAs) is evaluated. The new alert policy is deployed in the IT infrastructure.

Reduction of alerts in information technology systems

A system and method for maintaining objects in storage elements includes maintaining information regarding which storage elements are storing particular objects and responding to a request to update an object by using maintained information to determine which of the storage elements store a copy of the object. Each storage element is instructed to invalidate the copy of the object, and an update of the object is performed after each storage element that includes the copy of the object indicates that the storage element has invalidated the copy of the object or the storage element is determined to be unresponsive.

Daniela Rosu

Papers

System and method for achieving different levels of data consistency

System and method for achieving deferred invalidation consistency

Methods and apparatus for selective workload off-loading across multiple data centers

Reduction of alerts in information technology systems

System and method for achieving strong data consistency