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Schiavoni, Valerio
Nom
Schiavoni, Valerio
Affiliation principale
Fonction
Maitre-Assistant, Coordinateur Complex Systems and Big Data Competence Centre
Email
valerio.schiavoni@unine.ch
Identifiant ORCID
Résultat de la recherche
Voici les éléments 1 - 10 sur 39
- PublicationMétadonnées seulementEvaluating the Cost and Robustness of Self-organizing Distributed Hash Tables(: Springer, 2016-6-5)
; ; ; Self-organizing construction principles are a natural fit for large-scale distributed system in unpredictable deployment environments. These principles allow a system to systematically converge to a global state by means of simple, uncoordinated actions by individual peers. Indexing services based on the distributed hash table (DHT) abstraction have been established as a solid foundation for large-scale distributed applications. For most DHTs, the creation and maintenance of the overlay structure relies on the exploration and update of an already stabilized structure. We evaluate in this paper the practical interest of self-organizing principles, and in particular gossip-based overlay construction protocols, to bootstrap and maintain various DHT implementations. Based on the seminal work on T-Chord, a self-organizing version of Chord using the T-Man overlay construction service, we contribute three additional self-organizing DHTs: T-Pastry, T-Kademlia and T-Kelips. We conduct an experimental evaluation of the cost and performance of each of these designs using a prototype implementation. Our conclusion is that, while providing equivalent performance in a stabilized system, self-organizing DHTs are able to sustain and recover from higher level of churn than their explicitly-created counterparts, and should therefore be considered as a method of choice for deploying robust indexing layers in adverse environments. - PublicationMétadonnées seulementSPADS: Publisher Anonymization for DHT Storage(: IEEE, 2010-8-25)
; ; ; Valerio, JoséMany distributed applications, such as collaborative Web mapping, collaborative feedback and ranking, or bug reporting systems, rely on the aggregation of privacy-sensitive information gathered from human users. This information is typically aggregated at servers and later used as the basis for some collaborative service. Expecting that clients trust that the user-centric information will not be used for malevolent purposes is not realistic in a fully distributed setting where nodes are not under the control of a single administrative domain. Moreover, most of the time the origin of the data is of small importance when computing the aggregation onto which these services are based. Trust problems can be evinced by ensuring that the identity of the user is dropped before the data can actually be used, a process called publisher anonymization. Such a property shall be guaranteed even if a set of servers is colluding to spy on some user. This also requires that malevolent users cannot harm the service by sending any number of items without being traceable due to publisher anonymization. Rate limitation and decoupled authentication are the two mechanisms that ensure that these cheating users have a limited impact on the system. This paper presents SPADS, a system that interfaces to any DHT and supports the three objectives of publisher anonymization, rate limitation and decoupled authentication. The evaluation of a deployed prototype on a cluster assesses its performance and small footprint. - PublicationMétadonnées seulementWHISPER: Middleware for Confidential Communication in Large-Scale Networks(2011-6-20)
; ; A wide range of distributed applications requires some form of confidential communication between groups of users. In particular, the messages exchanged between the users and the identity of group members should not be visible to external observers. Classical approaches to confidential group communication rely upon centralized servers, which limit scalability and represent single points of failure. In this paper, we present WHISPER, a fully decentralized middleware that supports confidential communications within groups of nodes in large-scale systems. It builds upon a peer sampling service that takes into account network limitations such as NAT and firewalls. WHISPER implements confidentiality in two ways: it protects the content of messages exchanged between the members of a group, and it keeps the group memberships secret to external observers. Using multi-hops paths allows these guarantees to hold even if attackers can observe the link between two nodes, or be used as content relays for NAT bypassing. Evaluation in real-world settings indicates that the price of confidentiality remains reasonable in terms of network load and processing costs. - PublicationMétadonnées seulementA Component-Based Middleware Platform for Reconfigurable Service-Oriented Architectures(2011-6-7)
; Stefani, Jean-Bernard - PublicationMétadonnées seulementA Performance Evaluation of Erasure Coding Libraries for Cloud-Based Data StoresErasure codes have been widely used over the last decade to implement reliable data stores. They offer interesting trade-offs between efficiency, reliability, and storage overhead. Indeed, a distributed data store holding encoded data blocks can tolerate the failure of multiple nodes while requiring only a fraction of the space necessary for plain replication, albeit at an increased encoding and decoding cost. There exists nowadays a number of libraries implementing several variations of erasure codes, which notably differ in terms of complexity and implementation-specific optimizations. Seven years ago, Plank et al. [14] have conducted a comprehensive performance evaluation of open-source erasure coding libraries available at the time to compare their raw performance and measure the impact of different parameter configurations. In the present experimental study, we take a fresh perspective at the state of the art of erasure coding libraries. Not only do we cover a wider set of libraries running on modern hardware, but we also consider their efficiency when used in realistic settings for cloud-based storage, namely when deployed across several nodes in a data centre. Our measurements therefore account for the end-to-end costs of data accesses over several distributed nodes, including the encoding and decoding costs, and shed light on the performance one can expect from the various libraries when deployed in a real system. Our results reveal important differences in the efficiency of the different libraries, notably due to the type of coding algorithm and the use of hardware-specific optimizations.
- PublicationMétadonnées seulement
- PublicationMétadonnées seulementSplayNet: Distributed User-Space Topology EmulationNetwork emulation allows researchers to test distributed applications on diverse topologies with fine control over key properties such as delays, bandwidth, congestion, or packet loss. Current approaches to network emulation require using dedicated machines and low-level operating system support. They are generally limited to one user deploying a single topology on a given set of nodes, and they require complex management. These constraints restrict the scope and impair the uptake of network emulation by designers of distributed applications. We propose a set of novel techniques for network emulation that operate only in user-space without specific operating system support. Multiple users can simultaneously deploy several topologies on shared physical nodes with minimal setup complexity. A modular network model allows emulating complex topologies, including congestion at inner routers and links, without any centralized orchestration nor dedicated machine. We implement our user-space network emulation mechanisms in SplayNet, as an extension of an open-source distributed testbed. Our evaluation with a representative set of applications and topologies shows that SplayNet provides accuracy comparable to that of low-level systems based on dedicated machines, while offering better scalability and ease of use.
- PublicationMétadonnées seulementCoFeed: privacy-preserving Web search recommendation based on collaborative aggregation of interest feedback(2013-1-13)
; ; ; ; Valerio, JoséSearch engines essentially rely on the structure of the graph of hyperlinks. Although accurate for the main trend, this is not effective when some query is ambiguous. Leveraging semantic information by the mean of interest matching allows proposing complementary results that are tailored to the user's expectations. This paper proposes a collaborative search companion system, CoFeed, that collects user search queries and that considers feedback to build user-centric and document-centric profiling information. Over time, the system constructs ranked collections of elements that maintain the required information diversity and enhance the user search experience by presenting additional results tailored to the user's interest space. This collaborative search companion requires a supporting architecture adapted to large user populations generating high request loads. To that end, it integrates mechanisms for ensuring scalability and load balancing of the service under varying loads and user interest distributions. Moreover, collecting the recommendation data poses the problem of users’ privacy, and the bias one peer can induce to the system by sending fake recommendations. To that end, CoFeed ensures both publisher anonymity and rate limitation. With the former, the origin of the data is never known by the server that processes it, even if several servers collude to spy on some user. The latter, combined with decoupled authentication, allows to minimize the influence of cheating peers sending fake recommendations. Experiments with a deployed prototype highlight the efficiency of the system by analyzing improvement in search relevance, computational cost, scalability and load balancing. - PublicationMétadonnées seulement