On Democracy in Peer-to-Peer systems

The information flow inside a P2P network is highly dependent on the network structure. In order to ease the diffusion of relevant data toward interested peers, many P2P protocols gather similar nodes by putting them in direct contact. With this approach the similarity between nodes is computed in a point-to-point fashion: each peer individually identifies the nodes that share similar interests with it. This leads to the creation of a sort of "private" communities, limited to each peer neighbors list. This "private" knowledge do not allow to identify the features needed to discover and characterize the correlations that collect similar peers in broader groups. In order to let these correlations to emerge, the collective knowledge of peers must be exploited. One common problem to overcome in order to avoid the "private" vision of the network, is related to how distributively determine the representation of a community and how nodes may decide to belong to it. We propose to use a gossip-like approach in order to let peers elect and identify leaders of interest communities. Once leaders are elected, their profiles are used as community representatives. Peers decide to adhere to a community or another by choosing the most similar representative they know about

Structured Overlay For Heterogeneous Environments: Design and Evaluation of Oscar

Recent years have seen advances in building large internet-scale index structures, generally known as structured overlays. Early structured overlays realized distributed hash tables (DHTs) which are ill suited for anything but exact queries. The need to support range queries necessitate systems which can handle uneven load distributions. However such systems suffer from practical problems - including poor latency, disproportionate bandwidth usage at participating peers or unrealistic assumptions on peers' homogeneity, in terms of available storage or bandwidth resources. In this paper we consider a system which is capable not only to support uneven load distributions but also to operate in heterogeneous environments, where each peer can autonomously decide how much of its resources to contribute to the system. We provide the theoretical foundations of realizing such a network and present a newly proposed system Oscar based on these principles. Oscar can construct efficient overlays given arbitrary load distributions by employing a novel scalable network sampling technique. The simulations of our system validate the theory and evaluate Oscar's performance under typical challenges encountered in real-life large-scale networked systems, including participant heterogeneity, faults and skewed and dynamic load-distributions. Thus the Oscar distributed index fills in an important gap in the family of structured overlays, bringing into life a practical internet-scale index, which can play a crucial role in enabling data-oriented applications distributed over wide-area networks

GosSkip, an Efficient, Fault-tolerant and Self Organizing Overlay using Gossip-based Construction and Skip-lists Principles

International audienceThis paper presents GosSkip, a self organizing and fully distributed overlay that provides a scalable support to data storage and retrieval in dynamic environments. The structure of GosSkip, while initially possibly chaotic, eventually matches a perfect set of Skip-list-like structures, where no hash is used on data attributes, thus preserving semantic locality and permitting range queries. The use of epidemic-based protocols is the key to scalability, fairness and good behavior of the protocol under churn, while preserving the simplicity of the approach and maintaining O(log(N)) state per peer and O(log(N)) routing costs. In addition, we propose a simple and efficient mechanism to exploit the presence of multiple data items on a single physical node. GosSkip's behavior in both a static and a dynamic scenario is further conveyed by experiments with an actual implementation and real traces of a peer to peer workload

RootChord

We present a distributed data structure, which we call "RootChord". To our knowledge, this is the first distributed hash table which is able to adapt to changes in the size of the network and answer lookup queries within a guaranteed two hops while maintaining a routing table of size Theta(sqrt(N)). We provide pseudocode and analysis for all aspects of the protocol including routing, joining, maintaining, and departing the network. In addition we discuss the practical implementation issues of parallelization, data replication, remote procedure calls, dead node discovery, and network convergence