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Schiavoni, Valerio

Nom
Schiavoni, Valerio
Affiliation principale
Site web
Fonction
Maitre-Assistant, Coordinateur Complex Systems and Big Data Competence Centre
Email
valerio.schiavoni@unine.ch
Identifiants
https://libra.unine.ch/handle/123456789/293
_
0000-0003-1493-6603

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  • Publication
    Accès libre
    Block placement strategies for fault-resilient distributed tuple spaces: an experimental study
    (: Springer, 2017-6-19)
    Barbi, Roberta
    ;
    Buravlev, Vitaly
    ;
    Antares Mezzina, Claudio
    ;
    Schiavoni, Valerio 
    The tuple space abstraction provides an easy-to-use programming paradigm for distributed applications. Intuitively, it behaves like a distributed shared memory, where applications write and read entries (tuples). When deployed over a wide area network, the tuple space needs to efficiently cope with faults of links and nodes. Erasure coding techniques are increasingly popular to deal with such catastrophic events, in particular due to their storage efficiency with respect to replication. When a client writes a tuple into the system, this is first striped into k blocks and encoded into 𝑛>𝑘 blocks, in a fault-redundant manner. Then, any k out of the n blocks are sufficient to reconstruct and read the tuple. This paper presents several strategies to place those blocks across the set of nodes of a wide area network, that all together form the tuple space. We present the performance trade-offs of different placement strategies by means of simulations and a Python implementation of a distributed tuple space. Our results reveal important differences in the efficiency of the different strategies, for example in terms of block fetching latency, and that having some knowledge of the underlying network graph topology is highly beneficial.
  • Publication
    Métadonnées seulement
    SplayNet: Distributed User-Space Topology Emulation
    (: Springer, 2013-12-22)
    Schiavoni, Valerio 
    ;
    Rivière, Etienne 
    ;
    Felber, Pascal 
    Network 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.
  • Publication
    Métadonnées seulement
    Evaluating the Cost and Robustness of Self-organizing Distributed Hash Tables
    (: Springer, 2016-6-5)
    Krasikova, Sveta
    ;
    Carvajal Gómez, Raziel 
    ;
    Borba Ribeiro, Heverson 
    ;
    Rivière, Etienne 
    ;
    Schiavoni, Valerio 
    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.
  • Publication
    Métadonnées seulement
    TOPiCo: Detecting Most Frequent Items from Multiple High-Rate Event Streams
    (: ACM, 2015-6-29)
    Schiavoni, Valerio 
    ;
    Rivière, Etienne 
    ;
    Sutra, Pierre 
    ;
    Felber, Pascal 
    ;
    Matos, Miguel
    ;
    Oliveira, Rui
    Systems such as social networks, search engines or trading platforms operate geographically distant sites that continu- ously generate streams of events at high-rate. Such events can be access logs to web servers, feeds of messages from participants of a social network, or financial data, among others. The ability to timely detect trends and popularity variations is of paramount importance in such systems. In particular, determining what are the most popular events across all sites allows to capture the most relevant informa- tion in near real-time and quickly adapt the system to the load. This paper presents TOPiCo, a protocol that com- putes the most popular events across geo-distributed sites in a low cost, bandwidth-efficient and timely manner. TOPiCo starts by building the set of most popular events locally at each site. Then, it disseminates only events that have a chance to be among the most popular ones across all sites, significantly reducing the required bandwidth. We give a correctness proof of our algorithm and evaluate TOPiCo using a real-world trace of more than 240 million events spread across 32 sites. Our empirical results shows that (i) TOPiCo is timely and cost-efficient for detecting popular events in a large-scale setting, (ii) it adapts dynamically to the distribution of the events, and (iii) our protocol is particularly efficient for skewed distributions.
  • Publication
    Métadonnées seulement
    Autonomous Multi-Dimensional Slicing for Large-Scale Distributed Systems
    (: Springer, 2014-6-4)
    Pasquet, Mathieu
    ;
    Maia, Francisco
    ;
    Rivière, Etienne 
    ;
    Schiavoni, Valerio 
    Slicing is a distributed systems primitive that allows to autonomously partition a large set of nodes based on node-local attributes. Slicing is decisive for automatically provisioning system resources for different services, based on their requirements or importance. One of the main limitations of existing slicing protocols is that only single dimension attributes are considered for partitioning. In practical settings, it is often necessary to consider best compromises for an ensemble of metrics. In this paper we propose an extension of the slicing primitive that allows multi-attribute distributed systems slicing.Our protocol employs a gossip-based approach that does not require centralized knowledge and allows self-organization. It leverages the notion of domination between nodes, forming a partial order between multi-dimensional points, in a similar way to SkyLine queries for databases. We evaluate and demonstrate the interest of our approach using large-scale simulations.
  • Publication
    Métadonnées seulement
  • Publication
    Métadonnées seulement
    Lightweight, Efficient, Robust Epidemic Dissemination
    (2013-1-13)
    Matos, Miguel
    ;
    Schiavoni, Valerio 
    ;
    Felber, Pascal 
    ;
    Oliveira, Rui
    ;
    Rivière, Etienne 
    Gossip-based protocols provide a simple, scalable, and robust way to disseminate messages in large-scale systems. In such protocols, messages are spread in an epidemic manner. Gossiping may take place between nodes using push, pull, or a combination. Push-based systems achieve reasonable latency and high resilience to failures but may impose an unnecessarily large redundancy and overhead on the system. At the other extreme, pull-based protocols impose a lower overhead on the network at the price of increased latencies. A few hybrid approaches have been proposed—typically pushing control messages and pulling data—to avoid the redundancy of high-volume content and single-source streams. Yet, to the best of our knowledge, no other system intermingles push and pull in a multiple-senders scenario, in such a way that data messages of one help in carrying control messages of the other and in adaptively adjusting its rate of operation, further reducing overall cost and improving both on delays and robustness. In this paper, we propose an efficient generic push-pull dissemination protocol, Pulp, which combines the best of both worlds. Pulp exploits the efficiency of push approaches, while limiting redundant messages and therefore imposing a low overhead, as pull protocols do. Pulp leverages the dissemination of multiple messages from diverse sources: by exploiting the push phase of messages to transmit information about other disseminations, Pulp enables an efficient pulling of other messages, which themselves help in turn with the dissemination of pending messages. We deployed Pulp on a cluster and on PlanetLab. Our results demonstrate that Pulp achieves an appealing trade-off between coverage, message redundancy, and propagation delay.