392 research outputs found

    Deterministic Object Management in Large Distributed Systems

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    Caching is a widely used technique to improve the scalability of distributed systems. A central issue with caching is maintaining object replicas consistent with their master copies. Large distributed systems, such as the Web, typically deploy heuristic-based consistency mechanisms, which increase delay and place extra load on the servers, while not providing guarantees that cached copies served to clients are up-to-date. Server-driven invalidation has been proposed as an approach to strong cache consistency, but it requires servers to keep track of which objects are cached by which clients. We propose an alternative approach to strong cache consistency, called MONARCH, which does not require servers to maintain per-client state. Our approach builds on a few key observations. Large and popular sites, which attract the majority of the traffic, construct their pages from distinct components with various characteristics. Components may have different content types, change characteristics, and semantics. These components are merged together to produce a monolithic page, and the information about their uniqueness is lost. In our view, pages should serve as containers holding distinct objects with heterogeneous type and change characteristics while preserving the boundaries between these objects. Servers compile object characteristics and information about relationships between containers and embedded objects into explicit object management commands. Servers piggyback these commands onto existing request/response traffic so that client caches can use these commands to make object management decisions. The use of explicit content control commands is a deterministic, rather than heuristic, object management mechanism that gives content providers more control over their content. The deterministic object management with strong cache consistency offered by MONARCH allows content providers to make more of their content cacheable. Furthermore, MONARCH enables content providers to expose internal structure of their pages to clients. We evaluated MONARCH using simulations with content collected from real Web sites. The results show that MONARCH provides strong cache consistency for all objects, even for unpredictably changing ones, and incurs smaller byte and message overhead than heuristic policies. The results also show that as the request arrival rate or the number of clients increases, the amount of server state maintained by MONARCH remains the same while the amount of server state incurred by server invalidation mechanisms grows

    Adaptive Caching of Distributed Components

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    Die Zugriffslokalität referenzierter Daten ist eine wichtige Eigenschaft verteilter Anwendungen. Lokales Zwischenspeichern abgefragter entfernter Daten (Caching) wird vielfach bei der Entwicklung solcher Anwendungen eingesetzt, um diese Eigenschaft auszunutzen. Anschliessende Zugriffe auf diese Daten können so beschleunigt werden, indem sie aus dem lokalen Zwischenspeicher bedient werden. Gegenwärtige Middleware-Architekturen bieten dem Anwendungsprogrammierer jedoch kaum Unterstützung für diesen nicht-funktionalen Aspekt. Die vorliegende Arbeit versucht deshalb, Caching als separaten, konfigurierbaren Middleware-Dienst auszulagern. Durch die Einbindung in den Softwareentwicklungsprozess wird die frühzeitige Modellierung und spätere Wiederverwendung caching-spezifischer Metadaten gewährleistet. Zur Laufzeit kann sich das entwickelte System außerdem bezüglich der Cachebarkeit von Daten adaptiv an geändertes Nutzungsverhalten anpassen.Locality of reference is an important property of distributed applications. Caching is typically employed during the development of such applications to exploit this property by locally storing queried data: Subsequent accesses can be accelerated by serving their results immediately form the local store. Current middleware architectures however hardly support this non-functional aspect. The thesis at hand thus tries outsource caching as a separate, configurable middleware service. Integration into the software development lifecycle provides for early capturing, modeling, and later reuse of cachingrelated metadata. At runtime, the implemented system can adapt to caching access characteristics with respect to data cacheability properties, thus healing misconfigurations and optimizing itself to an appropriate configuration. Speculative prefetching of data probably queried in the immediate future complements the presented approach

    Quantum cryptography: key distribution and beyond

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    Uniquely among the sciences, quantum cryptography has driven both foundational research as well as practical real-life applications. We review the progress of quantum cryptography in the last decade, covering quantum key distribution and other applications.Comment: It's a review on quantum cryptography and it is not restricted to QK

    Mobility-aware Software-Defined Service-Centric Networking for Service Provisioning in Urban Environments

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    Disruptive applications for mobile devices, such as the Internet of Things, Connected and Autonomous Vehicles, Immersive Media, and others, have requirements that the current Cloud Computing paradigm cannot meet. These unmet requirements bring the necessity to deploy geographically distributed computing architectures, such as Fog and Mobile Edge Computing. However, bringing computing close to users has its costs. One example of cost is the complexity introduced by the management of the mobility of the devices at the edge. This mobility may lead to issues, such as interruption of the communication with service instances hosted at the edge or an increase in communication latency during mobility events, e.g., handover. These issues, caused by the lack of mobility-aware service management solutions, result in degradation in service provisioning. The present thesis proposes a series of protocols and algorithms to handle user and service mobility at the edge of the network. User mobility is characterized when user change access points of wireless networks, while service mobility happens when services have to be provisioned from different hosts. It assembles them in a solution for mobility-aware service orchestration based on Information-Centric Networking (ICN) and runs on top of Software-Defined Networking (SDN). This solution addresses three issues related to handling user mobility at the edge: (i) proactive support for user mobility events, (ii) service instance addressing management, and (iii) distributed application state data management. For (i), we propose a proactive SDN-based handover scheme. For (ii), we propose an ICN addressing strategy to remove the necessity of updating addresses after service mobility events. For (iii), we propose a graph-based framework for state data placement in the network nodes that accounts for user mobility and latency requirements. The protocols and algorithms proposed in this thesis were compared with different approaches from the literature through simulation. Our results show that the proposed solution can reduce service interruption and latency in the presence of user and service mobility events while maintaining reasonable overhead costs regarding control messages sent in the network by the SDN controller

    The flight of Alsomitra macrocarpa

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    Alsomitra macrocarpa is a gliding diaspore which grows on tall trees in tropical Asian forests. It does not rely on gusts nor even on a slight breeze to fly up to hundreds of meters. It is a low aspect ratio wing, which defies the conventional aerodynamic argument that efficient gliders need to be slender. Compared to pappose seeds like the dandelion, Alsomitra macrocarpa has a higher wing loading, yet it reaches a comparable terminal velocity. It also achieves a stable flight in the absence of both a vertical stabiliser and active control. What enables these remarkable flight abilities, which inspired the design of the first manned gliders, are yet to be understood. The investigation herein utilised image analysis, three-dimensional scans and wind tunnel tests. The morphological study highlighted Alsomitra macrocarpa’s uniqueness in terms of dimensions and shape. Through the use of depth cameras, the gliding path of 15 seeds was recorded. While existing literature treats Alsomitra macrocarpa as a flat, two-dimensional shape, drop tests evidenced a preferential flight orientation for every seed sample. Hence, and contrary to previous belief, the membrane wing has an intrados and an extrados. The majority of the seeds presented a helical path, while some moved in a straight oscillatory path that has not been previously reported, with oscillations on the vertical and horizontal plane. This gliding trajectory assumed to be two-dimensional, could be described by a simplified dynamics model. The phugoid style flight coupled the horizontal motion of a tumbling wing with the oscillation of a fluttering wing. Wind tunnel tests revealed how the membrane wing undergoes spanwise deformation under the loads experienced during a glide. This deformation displaces the aerodynamic centre from the plane of the membrane wing. Low-order dynamical models, which included a non-uniform mass distribution, were employed to recreate these oscillations in the vertical plane and showed good qualitative agreement with the experiments. Overall, this work provides new insights into the remarkably stable and efficient flight of Alsomitra macrocarpa. The aerodynamic conditions under which these seeds fly are in the range experienced by Micro Aerial Vehicles (MAVs). Thus, the outcomes of this thesis could aid the design of more efficient MAVs, just as early aviation pioneers were inspired when they saw Alsomitra macrocarpa glide down through the forest canopy

    Enabling Hyperscale Web Services

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    Modern web services such as social media, online messaging, web search, video streaming, and online banking often support billions of users, requiring data centers that scale to hundreds of thousands of servers, i.e., hyperscale. In fact, the world continues to expect hyperscale computing to drive more futuristic applications such as virtual reality, self-driving cars, conversational AI, and the Internet of Things. This dissertation presents technologies that will enable tomorrow’s web services to meet the world’s expectations. The key challenge in enabling hyperscale web services arises from two important trends. First, over the past few years, there has been a radical shift in hyperscale computing due to an unprecedented growth in data, users, and web service software functionality. Second, modern hardware can no longer support this growth in hyperscale trends due to a decline in hardware performance scaling. To enable this new hyperscale era, hardware architects must become more aware of hyperscale software needs and software researchers can no longer expect unlimited hardware performance scaling. In short, systems researchers can no longer follow the traditional approach of building each layer of the systems stack separately. Instead, they must rethink the synergy between the software and hardware worlds from the ground up. This dissertation establishes such a synergy to enable futuristic hyperscale web services. This dissertation bridges the software and hardware worlds, demonstrating the importance of that bridge in realizing efficient hyperscale web services via solutions that span the systems stack. The specific goal is to design software that is aware of new hardware constraints and architect hardware that efficiently supports new hyperscale software requirements. This dissertation spans two broad thrusts: (1) a software and (2) a hardware thrust to analyze the complex hyperscale design space and use insights from these analyses to design efficient cross-stack solutions for hyperscale computation. In the software thrust, this dissertation contributes uSuite, the first open-source benchmark suite of web services built with a new hyperscale software paradigm, that is used in academia and industry to study hyperscale behaviors. Next, this dissertation uses uSuite to study software threading implications in light of today’s hardware reality, identifying new insights in the age-old research area of software threading. Driven by these insights, this dissertation demonstrates how threading models must be redesigned at hyperscale by presenting an automated approach and tool, uTune, that makes intelligent run-time threading decisions. In the hardware thrust, this dissertation architects both commodity and custom hardware to efficiently support hyperscale software requirements. First, this dissertation characterizes commodity hardware’s shortcomings, revealing insights that influenced commercial CPU designs. Based on these insights, this dissertation presents an approach and tool, SoftSKU, that enables cheap commodity hardware to efficiently support new hyperscale software paradigms, improving the efficiency of real-world web services that serve billions of users, saving millions of dollars, and meaningfully reducing the global carbon footprint. This dissertation also presents a hardware-software co-design, uNotify, that redesigns commodity hardware with minimal modifications by using existing hardware mechanisms more intelligently to overcome new hyperscale overheads. Next, this dissertation characterizes how custom hardware must be designed at hyperscale, resulting in industry-academia benchmarking efforts, commercial hardware changes, and improved software development. Based on this characterization’s insights, this dissertation presents Accelerometer, an analytical model that estimates gains from hardware customization. Multiple hyperscale enterprises and hardware vendors use Accelerometer to make well-informed hardware decisions.PHDComputer Science & EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/169802/1/akshitha_1.pd

    Reformulación y categorías vecinas: un tratamiento teórico-experimental a través del marcador discursivo o sea en español = Reformulation and neighboring categories: a theoretical-experimental approach through the Sp. discourse marker o sea

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    Recientemente, los estudios sobre reformulación han generado un debate teórico en torno a esta función y su tratamiento semasiológico-onomasiológico: algunos autores abogan por una distinción clara de esta función frente a otras, como la conclusión o la corrección (Pons 2013, 2017). Otros autores defienden que la reformulación presenta subtipos basados en esas otras funciones, expresadas por los mismos marcadores discursivos: los reformuladores (Murillo 2016). La primera postura va de lo onomasiológico a lo semasiológico: la reformulación, la paráfrasis, la conclusión y la corrección son cuatro relaciones discursivas diferenciables (Pons 2013) que pueden expresarse a través de los mismos marcadores discursivos. Esto, no obstante, no significa que todas ellas sean subtipos supeditados a la función predominante (en el caso de los marcadores de reformulación, la reformulación discursiva): se trata, más bien, de una muestra de la polifuncionalidad de los marcadores (Pons 2017). La segunda postura va de lo semasiológico a lo onomasiológico: la conclusión o la corrección son subtipos de la reformulación porque la mayoría de los marcadores de reformulación las expresan en varias lenguas (Murillo 2016). Este hecho es un indicador de la relación existente entre ellas, que va más allá de la polisemia de los marcadores discursivos. Ambas posturas son lícitas: se oponen entre ellas por los argumentos y las bases teóricas que las sustentan; sin embargo, ninguna puede anular a la otra. Los investigadores las seguirán en función de su aplicabilidad en sus trabajos. Esto ha llevado a que el debate alcance un punto muerto que aceptará más estudios de caso e ideas pero que, desde una visión teórica, no conducirá hacia una resolución definitiva. Como resultado, el estado de la reformulación es el de una función que, aparentemente, ha perdido sus límites definitorios: ¿son reformulación, conclusión y corrección tan parecidas, como sus marcadores parecen mostrar, o es posible detectar rasgos que las distingan? Frente a este problema teórico, el presente trabajo ofrece una propuesta experimental para solventarlo. Dicha propuesta tratará la reformulación con el método eye-tracking (Just, Adam y Carpenter 1980; Loureda et al. 2013, 2016): este método se basa en la hipótesis ojo-mente, que asume que todo contenido observado está siendo cognitivamente procesado. A partir de un conjunto de movimientos (fijaciones y regresiones) y su duración en varias etapas de lectura (first, second y total reading time), se obtendrán patrones de procesamiento para contextos de paráfrasis, reformulación, conclusión y corrección expresados con y sin marcador discursivo. Los datos obtenidos reflejarán: (1) si la reformulación se parece o no a sus otras funciones vecinas, y (2) si los marcadores de reformulación se procesan igual en contextos de reformulación, conclusión o corrección o si, realmente, son un ejemplo de polisemia. Para medir la polisemia, se ha seleccionado el marcador de reformulación o sea en español: es la muestra más clara del problema expuesto, ya que es el marcador reformulador prototípico pero, además, codifica otras funciones, como la paráfrasis, la conclusión y la corrección, junto con algunos valores modales y de formulación. Los resultados permitirán al investigador decantarse hacia una postura u otra.A recent debate on reformulation and its semasiological-onomasiological treatment has become the focus of different studies published in the field. Some researchers argue for a clear distinction between reformulation and other functions such as conclusión or correction (Pons 2013, 2017); others defend the existence of different subtypes of reformulation based on such other functions which, in turn, are expressed by the same group of discourse markers in different languages (Murillo 2016). The former approach goes from onomasiology to semasiology: reformulation, paraphrase, conclusión and correction are four distinguishable functions which can be expressed by the same discourse markers; however, this does not mean that all them are subtypes of their predominant function (reformulation in reformulation markers) (Pons 2013). Rather, this shows the polyfunctionality behind these markers (Pons 2017). The latter is a semasiological-onomasiological approach: conclusión or correction are reformulation subtypes because most of the reformulation markers express them in varios languages (Murillo 2016). This fact suggests the relationship they share, which goes beyond discourse markers polysemy. Both approaches are valid despite their arguments and theoretical basis are opposed. Researchers follow one or another depending on the type of study developed. This situation however, should be clarified: theoretically, no answers can be proposed as definitive. As a result, reformulation has lost its defining boundaries: are reformulation, conclusión and correction as similar as their discourse markers seem to demonstrate? It is posible to find distinguishing features? This dissertation presents an eye-tracking experimental proposal to solve these problems (Just, Adam y Carpenter 1980; Loureda et al. 2013, 2016): this method is based on the eye-mind hypothesis, which assumes that all things observed are cognitively processed. A set of processing patterns will be obtained by considering a series of eye-movements (fixations and regressions) and their corresponding duration in different reading stages (First, second and total reading time). Such patterns will define experimentally paraphrase, reformulation, conclusión and correction expressed with and without a discourse marker. Results will show: (1) if reformulation is or not similar to other neighboring functions, and (2) if reformulation markers are processed in the same way in reformulative, conclusive or corrective contexts or if they are polysemic. Polysemy will be addressed by analyzing the Sp. discourse marker o sea. This marker is the most adequate ítem to account for this problem: it is the most prototypical reformulation marker which, in turn, expresses other functions such as paraphrase, conclusión or correction. Results will allow to assume one or other theoretical approach

    Scalable hosting of web applications

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    Modern Web sites have evolved from simple monolithic systems to complex multitiered systems. In contrast to traditional Web sites, these sites do not simply deliver pre-written content but dynamically generate content using (one or more) multi-tiered Web applications. In this thesis, we addressed the question: How to host multi-tiered Web applications in a scalable manner? Scaling up a Web application requires scaling its individual tiers. To this end, various research works have proposed techniques that employ replication or caching solutions at different tiers. However, most of these techniques aim to optimize the performance of individual tiers and not the entire application. A key observation made in our research is that there exists no elixir technique that performs the best for allWeb applications. Effective hosting of a Web application requires careful selection and deployment of several techniques at different tiers. To this end, we present several caching and replication strategies, such as GlobeCBC, GlobeDB and GlobeTP, to improve the scalability of different tiers of a Web application. While these techniques and systems improve the performance of the individual tiers (and eventually the application), an application's administrator is not only interested in the performance of its individual tiers but also in its endto- end performance. To this end, we propose a resource provisioning approach that allows us to choose the best resource configuration for hosting a Web application such that its end-to-end response time can be optimized with minimum usage of resources. The proposed approach is based on an analytical model for multi-tier systems, which allows us to derive expressions for estimating the mean end-to-end response time and its variance.Steen, M.R. van [Promotor]Pierre, G.E.O. [Copromotor
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