DotSlash - Creating Content Distribution Networks on Demand

Traditional content distribution networks, such as Akamai, are well-suited for static web services that routinely experience large traffic volumes. They are unsuited for active content, i.e., content generated by scripts from databases, and web sites that are unlikely to receive significant number of requests. However, a few such sites will invariably experience their "fifteen minutes of fame", typically by being mentioned on a high-volume news site such as SlashDot or CNN. Such flashcrowds or "slashdot effect" will routinely cause single-server websites to collapse. We have designed and prototyped an autonomic web replication system, called DotSlash, that drafts rescue servers fully automatically, without user intervention. The system discovers suitable rescue servers via wide-area service location, either among peer servers or from a dedicated pool of rescue servers, allocates them for temporary use and redirects requests to them. The system is completely transparent to clients and does not require URL rewriting or other client modifications. We have designed two versions. The first, an Apache extension, deals only with static content, e.g., HTML pages or media objects. The second version can also replicate and execute scripts remotely. We have prototyped the system for the common LAMP (Linux, Apache, MySQL and PHP) configuration and shown that a common benchmark for bulletin boards can be replicated without code changes, yielding capacity increases bounded only by the database server. Since many such systems, including most blogs, are bottlenecked by the web server, our system can significantly increase capacity and works even for extremely rapid load increases. We are currently investigating how such systems can be further extended by increasing the database capacity of read-mostly systems with loose consistency constraints

Relink Tangible and Intangible

Syracuse, as part of the Upstate New York used to be an essential economic center of the United States. This not only was resulting from its once influential salt industry and its easily accessed canal infrastructure, but also was heavily influenced by the industrial innovation. Without trained engineers, the people in Syracuse designed machines for excavating the earth and building the Erie Canal. And with easy transportation, goods and industrial products created and produced from Syracuse were shipped and transported. This brought prosper and wealth to the Syracuse. With new transportation technology development including the railways for trains and highways for car, Erie Canal lost its competitive advantage. As a result, industrial goods from Syracuse, with great qualities and quantities, can no longer find its market sufficient to consume all these production. A great number of factories were either relocate to other parts of the country, or shut down permanently. And the Erie Canal was transformed to a city road. The image of industrial prosperity had lost and left behind, were only traces of history. This tangible ruins and intangible image of prosperity is waiting to be reconnect, revitalize, reestablished. Architecture, as a device that can both protect and revitalize such cultural heritage, is to mediate and to link the tangible and intangible part of history. An industrial memorial that is composed of a spatial translation of such industrial image can be a great way to memorize, revitalize, and relink the tangible and the intangible of industrial culture heritage

DotSlash: A Scalable and Efficient Rescue System for Handling Web Hotspots

This paper describes DotSlash, a scalable and efficient rescue system for handling web hotspots. DotSlash allows different web sites to form a mutual-aid community, and use spare capacity in the community to relieve web hotspots experienced by any individual site. As a rescue system, DotSlash intervenes when a web site becomes heavily loaded, and is phased out once the workload returns to normal. It aims to complement existing web server infrastructure such as CDNs to handle short-term load spikes effectively, but is not intended to support a request load constantly higher than a web site's planned capacity. DotSlash is scalable, cost-effective, easy to use, self-configuring, and transparent to clients. It targets small web sites, although large web site can also benefit from it. We have implemented a prototype of DotSlash on top of Apache. Experiments show that DotSlash can provide an order of magnitude improvement for a web server in terms of the request rate supported and the data rate delivered to clients even if only HTTP redirect is used. Parts of this work may be applicable to other services such as the Grid computational services and media streaming

A Flexible and Efficient Protocol for Multi-Scope Service Registry Replication

Service registries play an important role in service discovery systems by accepting service registrations and answering service queries; they can serve a wide range of purposes, such as membership services, lookup services, and search services. To provide fault tolerant, and enhance scalability, availability and performance, service registries often need to be replicated. In this paper, we present Swift (Selective anti-entropy WIth FasT update propagation), a flexible and efficient protocol for multi-scope service registry replication. As consistency is a less of concern compared with availability in service registry replication, we choose to build Swift on top of anti-entropy to support high availability replication. Swift makes two contributions as follows. First, it defines a more general and flexible form of anti-entropy called selective anti-entropy, which extends the applicability of anti-entropy from full replication to partial replication by selectively reconciling inconsistent states between two replicas, and improves anti-entropy efficiency by fine controlling update propagation within each subset. Selective anti-entropy is the first that we are aware of in using anti-entropy to support generic partial replication. Secondly, Swift integrates service registry overlay networks with selective anti-entropy. Different topologies, such as full mesh and spanning tree, can be used for constructing service registry overlay networks. These overlay networks are used to propagate new updates quickly so as to minimize inconsistency among replicas. We have implemented Swift for replicating multi-scope Directory Agents in the Service Location Protocol. Our experience shows that Swift is flexible, efficient, and lightweight

DotSlash: Providing Dynamic Scalability to Web Applications with On-demand Distributed Query Result Caching

Scalability poses a significant challenge for today's web applications, mainly due to the large population of potential users. To effectively address the problem of short-term dramatic load spikes caused by web hotspots, we developed a self-configuring and scalable rescue system called DotSlash. The primary goal of our system is to provide dynamic scalability to web applications by enabling a web site to obtain resources dynamically, and use them autonomically without any administrative intervention. To address the database server bottleneck, DotSlash allows a web site to set up on-demand distributed query result caching, which greatly reduces the database workload for read mostly databases, and thus increases the request rate supported at a DotSlash-enabled web site. The novelty of our work is that our query result caching is on demand, and operated based on load conditions. The caching remains inactive as long as the load is normal, but is activated once the load is heavy. This approach offers good data consistency during normal load situations, and good scalability with relaxed data consistency for heavy load periods. We have built a prototype system for the widely used LAMP configuration, and evaluated our system using the RUBBoS bulletin board benchmark. Experiments show that a DotSlash-enhanced web site can improve the maximum request rate supported by a factor of 5 using 8 rescue servers for the RUBBoS submission mix, and by a factor of 10 using 15 rescue servers for the RUBBoS read-only mix

Fast Iterative Reconstruction for Multi-spectral CT by a Schmidt Orthogonal Modification Algorithm (SOMA)

Multi-spectral CT (MSCT) is increasingly used in industrial non-destructive testing and medical diagnosis because of its outstanding performance like material distinguishability. The process of obtaining MSCT data can be modeled as nonlinear equations and the basis material decomposition comes down to the inverse problem of the nonlinear equations. For different spectra data, geometric inconsistent parameters cause geometrical inconsistent rays, which will lead to mismatched nonlinear equations. How to solve the mismatched nonlinear equations accurately and quickly is a hot issue. This paper proposes a general iterative method to invert the mismatched nonlinear equations and develops Schmidt orthogonalization to accelerate convergence. The validity of the proposed method is verified by MSCT basis material decomposition experiments. The results show that the proposed method can decompose the basis material images accurately and improve the convergence speed greatly

Pressure measurement based on multi-waves fusion algorithm

Measuring the pressure of a pressure vessel accurately is one of fundamental requirements of the operation of many complex engineering systems. Ultrasonic technique has been proposed to be a good alteration of non-intrusive measurement. Based on the study of acoustoelastic effect and thin-shell theory, it has been identified that the travel-time changes of the critically refracted longitudinal wave (LCR wave) and other reflected longitudinal waves are all proportional to the inner pressure. Considering the information redundancy in these waves, we proposed an approach for pressure measurement by using the information fusion algorithm on multiple reflected longitudinal waves. In the paper, we discussed the fusion algorithm in details and proposed a pressure measurement model, which represents an accurate relationship between the pressure and the travel-time changes of multiple waves. Through the experiment, the analysis of data collected from experiment system showed that the pressure measurement based on the multi-wave model is notably more accurate than the one based on the single-wave model (the average relative error (ARE) can be less than 7.24% and the root-mean-square error (RMSE) can be lower than 0.3MPa)