1,720,965 research outputs found
Valid Query Answers exploting Node Virtualization
No full textThis thesis studies the problem of answering system-wide queries, satisfying the interval validity semantics, in a distributed system prone to continuous arrival and departure of participants. The interval validity semantic states that the query answer must be calculated considering contributions of at least all processes that remain in the distributed system for the whole query duration. It is impossible to satisfy this semantics in systems experiencing unbounded churn due to the lack of connectivity and path stability between processes. This thesis presents a novel architecture, named Virtual Tree, for building and maintaining a structured overlay network with guaranteed connectivity and path stability in settings characterized by bounded churn rate. The architecture includes a simple query answering algorithm that provides interval valid answers. The overlay network generated by the Virtual Tree architecture is a tree-shaped topology with virtual nodes constituted by clusters of processes and virtual links constituted by multiple communication links connecting processes located in adjacent virtual nodes. A bound has been formally proved on the churn rate for interval valid queries and it has been carried out an extensive experimental evaluation that shows the degree of robustness of the overlay network generated by the virtual tree architecture under different churn rates. The thesis also provide an application scenario of the proposed architecture in the field of the volunteer computing. The application scenario shows that Virtual Tree represents a fundamental building block for the architecture of a volunteer computing platform and its capability of offering valid queries enhances the performance of the system providing a better accuracy in the task-scheduling procedure
Virtual Tree: A robust architecture for interval valid queries in dynamic distributed systems
No full textThis paper studies the problem of answering aggregation queries, satisfying the interval validity semantics, in a distributed system prone to continuous arrival and departure of participants. The interval validity semantics states that the query answer must be calculated considering contributions of at least all processes that remained in the distributed system for the whole query duration. Satisfying this semantics in systems experiencing unbounded churn is impossible due to the lack of connectivity and path stability between processes. This paper presents a novel architecture, namely Virtual Tree, for building and maintaining a structured overlay network with guaranteed connectivity and path stability in settings characterized by bounded churn rate. The architecture includes a simple query answering algorithm that provides interval valid answers. The overlay network generated by the Virtual Tree architecture is a tree-shaped topology with virtual nodes constituted by clusters of processes and virtual links constituted by multiple communication links connecting processes located in adjacent virtual nodes. We formally prove a bound on the churn rate for interval valid queries in a distributed system where communication latencies are bounded by a constant unknown by processes. Finally, we carry out an extensive experimental evaluation that shows the degree of robustness of the overlay network generated by the virtual tree architecture under different churn rates. (C) 2013 Elsevier Inc. All rights reserved
Brief announcement: Distributed self-organizing event space partitioning for content-based publish/subscribe systems
No full textPublish/subscribe systems have commonly been divided in two large families on the basis of their event-selection model [2]: topic-based and content-based systems. The former trade reduced subscription expressiveness with simpler implementations and higher performance. Conversely, the latter allow to accurately map published data in a complex event schema on top of which expressive subscriptions can be defined, but incur the cost of more complex implementations that delivers reduced performance on large distributed settings. System developers are thus faced with a choice about which kind of system is best suited to the target application. A common solution to this dilemma lies in the event space partitioning [4] technique: the event schema is partitioned in a number of subspaces that are then statically mapped to topics. The partitioning must be globally known and subscribers are expected to subscribe those topics where subspaces that have a non-empty intersection with their content-based subscriptions have been mapped. Undesired events (false positives) can be filtered out at the receiver side. The event space partitioning granularity strongly affects the performance of such systems: if it is excessively coarse-grained too much resources are wasted to deliver false positives, while if it is too fine-grained the number of topics that will be generated, and that must be managed by the topic based system, could easily become huge. Current solutions [3] provide sub-optimal approximations that are calculated offline and then statically applied to the system. © 2011 Springer-Verlag
Virtual tree: A robust overlay network for ensuring interval valid queries in dynamic distributed systems
Get PDFToday's large scale distributed systems are characterized by strong dynamics caused by the inherent unreliability of their constituting elements (e.g. process and link failures, processes joining or leaving the system). This continuous dynamism has a strong negative impact on distributed algorithms designed to work on such systems. Regular registers [1], Replication [2], in-network aggregation[3], are all examples of such problem. © 2012 Springer-Verlag
Improving validity of query answering in dynamic systems
Get PDFLet us consider a large scale distributed system and a query executed on top of it where every process has to contribute to the result. Informally, a query satisfies the interval validity property if its result has been calculated by retrieving data from a set of processes containing at least all those ones that have been present in the system during the whole query lifetime. If the system is prone to churn, it is easy to show that a query cannot deterministically satisfy interval validity. In this paper we propose a novel algorithm that can be used to support distributed queries by increasing the probability of a query to satisfy interval validity. The algorithm strives to (i) reduce the query calculation time (to reduce the net effect of churn) and to (ii) increase the robustness of the overlay network it builds by clustering nodes into cliques of limited size in order for their implementation to be still practical. The paper provides a set of experiments that show the tradeoff between the churn rate and the number of times the interval validity is satisfied. Copyright 2010 ACM
User profiling and micro-accounting for smart energy management
No full textEnergy management, and in particular its efficient optimization, is one of the hot trends in the current days, both at the enterprise level (optimization of whole corporate/government buildings) and single-citizens'homes. Energy efficiency is generally function of out-door techniques- renewable energy, smart energy production and distribution, etc.- and in-door techniques; in particular, very few energy managers- each of us can be an energy manager of his own home- can state "who, when and why is consuming", conversely this knowledge is fundamental in order to diminish wasting of energy. Recent studies show that the energy wasted in the overall consumption is about the 30% of the total amount; examples of potential energy wasting are printers and PCs on during the night, status LED of different devices (TV, set-top-box, etc.) and/or lights, lights during normal day-light time, etc
Designing Highly Available Repositories for Heterogeneous Sensor Data in Open Home Automation Systems
No full textSmart home applications are currently implemented by vendor-specific systems managing mainly a few number of homogeneous sensors and actuators. However, the sharp increase of the number of intelligent devices in a house and the foreseen explosion of the smart home application market will change completely this vendor centric scenario towards open, expandable systems made up of a large number of cheap heterogeneous devices. As a matter of fact, new smart home solutions have to be able to taklewith scalability, dynamicity and heterogeneity requirements. In this paper we present the architecture of a basic building block, namely a distributed repository service, for smart home systems. The repository stores data from heterogeneous devices deployed in the house that can be then retrieved by context aware applications implementing some home automation functionalities. Our architecture, based on a DHT, offers a completely decentralized and reliable storage service able to offer complex query functionalities. © IFIP International Federation for Information Processing 2009
Energy management in smart spaces through the OPlatform
No full textEnergy management, and in particular its optimization, is one of the hot trends in the current days, both at the enterprise level (optimization of whole corporate/government buildings) and single-citizens' homes. The current trend is to provide knowledge about the micro(scopic) energy consumption. In our work we developed a platform, named OPlatform, for smart environments able to micro-account energy consumption of devices, at the level of each single power line, which allows at the same time the actuation of devices, thus being also an energy-aware domotic solution. After presenting the system architecture, consisting of a distributed system based on several OMeters (specifically designed hardware devices) and an OBox (an embedded PC hosting the software system), we present a preliminary case study, in which the OPlatform has been adopted in a small office, in order to highlight the concrete possible savings
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