Symmetric Replication for Structured Peer-to-Peer Systems

Structured peer-to-peer systems rely on replication as a basic means to provide fault-tolerance in presence of high churn. Most select replicas using either multiple hash functions, successor-lists, or leaf-sets. We show that all three alternatives have limitations. We present and provide full algorithmic speci¯cation for a generic replication scheme called symmetric replication which only needs O(1) message for every join and leave operation to maintain any replication degree. The scheme is applicable to all existing structured peer-to-peer systems, and can be implemented on-top of any DHT. The scheme has been implemented in our DKS system, and is used to do load-balancing, end-to-end fault-tolerance, and to increase the security by using distributed voting. We outline an extension to the scheme, implemented in DKS, which adds routing proximity to reduce latencies. The scheme is particularly suitable for use with erasure codes, as it can be used to fetch a random subset of the replicas for decoding

Atomic commitment in transactional DHTs

We investigate the problem of atomic commit in transactional database systems built on top of Distributed Hash Tables. DHTs provide a decentralized way to store and look up data. To solve the atomic commit problem we propose to use an adaption of Paxos commit as a non-blocking algorithm. We exploit the symmetric replication technique existing in the DKS DHT to determine which nodes are necessary to execute the commit algorithm. By doing so we achieve a lower number of communication rounds and a reduction of meta-data in contrast to traditional Three-Phase-Commit protocols. We also show how the proposed solution can cope with dynamism due to churn in DHTs. Our solution works correctly relying only on an inaccurate failure detection of node failure which is necessary for systems running over the Internet

Exploiting the Synergy Between Gossiping and Structured Overlays

In this position paper we argue for exploiting the synergy between gossip-based algorithms and structured overlay networks (SON). These two strands of research have both aimed at building fault-tolerant, dynamic, self-managing, and large-scale distributed systems. Despite the common goals, the two areas have, however, been relatively isolated. We focus on three problem domains where there is an untapped potential of using gossiping combined with SONs. We argue for applying gossip-based membership for ring-based SONs---such as Chord and Bamboo---to make them handle partition mergers and loopy networks. We argue that small world SONs---such as Accordion and Mercury---are specifically well-suited for gossip-based membership management. The benefits would be better graph-theoretic properties. Finally, we argue that gossip-based algorithms could use the overlay constructed by SONs. For example, many unreliable broadcast algorithms for SONs could be augmented with anti-entropy protocols. Similarly, gossip-based aggregation could be used in SONs for network size estimation and load-balancing purposes

DOH: A Content Delivery Peer-to-Peer Network

Many SMEs and non-pro¯t organizations su®er when their Web servers become unavailable due to °ash crowd e®ects when their web site becomes popular. One of the solutions to the °ash-crowd problem is to place the web site on a scalable CDN (Content Delivery Network) that replicates the content and distributes the load in order to improve its response time. In this paper, we present our approach to building a scalable Web Hosting environment as a CDN on top of a structured peer-to-peer system of collaborative web-servers integrated to share the load and to improve the overall system performance, scalability, availability and robustness. Unlike clusterbased solutions, it can run on heterogeneous hardware, over geographically dispersed areas. To validate and evaluate our approach, we have developed a system prototype called DOH (DKS Organized Hosting) that is a CDN implemented on top of the DKS (Distributed K-nary Search) structured P2P system with DHT (Distributed Hash table) functionality [9]. The prototype is implemented in Java, using the DKS middleware, the Jetty web-server, and a modi¯ed JavaFTP server. The proposed design of CDN has been evaluated by simulation and by evaluation experiments on the prototype

Fighting Cheating in P2P-based MMVEs with Disjoint Path Routing

In a P2P-based Massively Multiuser Virtual Environment (MMVE) where nodes cannot be trusted, replicating data on multiple nodes is a possibility to increase the reliability to obtain correct data. Current structured P2P networks mostly place replicas in such a way that queries for the replicas travel along similar paths. A malicious node in the common part of all paths can nullify the security gain of replicated data. We therefore propose to combine radix-based prefix routing with a symmetric replication scheme to gain disjoint paths to each of the replicas

SPLAD: scattering and placing data replicas to enhance long-term durability

Distributed storage systems have to ensure data availability and durability despite the occurrence of failures. To do so, many of them rely on replication mechanisms: for each piece of data, several replicas are stored. We show that the layout of the data block copies on the nodes, chiefly the way the copies are scattered, has a major impact on the reparation speed and thus on the data loss ratio. In this paper, we propose SLPAD, an approach that provides the ability: (i) to finely tune the proportion of common content stored by the nodes; and (ii) to control the storage load distribution while creating new data block copies. We propose a simulation model that allows us to present a long-term study of the impact of the data block copies layout and the system load on the data loss ratio.Les systèmes de stockage distribués doivent assurer la disponibilité des données et leur durabilité malgré l'occurrence de défaillances. Pour ce faire, beaucoup d'entre eux utilisent des mécanismes de réplication: pour chaque donnée, plusieurs copies sont stockées. Nous mon- trons que la disposition des copies des données sur les nœuds, surtout la façon dont elles sont dispersées, a un impact majeur sur la vitesse de réparation et donc sur le taux de perte. Dans ce papier, nous proposons SLPAD, une approche qui offre la possibilité: (i) de régler finement la proportion de contenu commun stocké par les nœuds; et (ii) de contrôler la répartition de la charge de stockage lors de la création nouvelles copies. Nous proposons un modèle de simulation qui nous permet de présenter une étude à long terme de l'impact de la disposition des copies des données et de la charge du système sur le taux de perte

Cryptocurrency Networks: A New P2P Paradigm

P2P networks are the mechanism used by cryptocurrencies to disseminate system information while keeping the whole system as much decentralized as possible. Cryptocurrency P2P networks have new characteristics that propose new challenges and avoid some problems of existing P2P networks. By characterizing the most relevant cryptocurrency network, Bitcoin, we provide details on different properties of cryptocurrency networks and their similarities and differences with standard P2P network paradigms. Our study allows us to conclude that cryptocurrency networks present a new paradigm of P2P networks due to the mechanisms they use to achieve high resilience and security. With this new paradigm, interesting research lines can be further developed, both in the focused field of P2P cryptocurrency networks and also when such networks are combined with other distributed scenarios

Um repositório chave-valor com garantia de localidade de dados

Orientador : Prof. Dr. Carmem Satie HaraDissertação (mestrado) - Universidade Federal do Paraná, Setor de Ciências Exatas, Programa de Pós-Graduação em Informática. Defesa: Curitiba, 09/08/2016Inclui referências : f. 67-76Resumo: Grandes volumes de dados produzidos diariamente trouxeram desafios envolvendo a definição de formas eficientes de como extraí-los, armazená-los e acessá-los. Entretanto, soluções tradicionais de bancos de dados não se mostraram eficientes diante de tais desafios, principalmente no requisito de escalabilidade. Uma possível abordagem para prover escalabilidade horizontal aos sistemas gerenciadores de banco de dados é a adoção de uma arquitetura estratificada, tendo como base um sistema de armazenamento distribuído com uma interface simples para o acesso a dados remotamente armazenados. Esta dissertação apresenta o ALOCS, um repositório distribuído de dados que adota o modelo chave-valor, mas que permite a alocação de um conjunto de pares agrupados em uma única estrutura, cuja localidade é controlada pela aplicação usuária do sistema. O controle de localidade permite que dados usualmente utilizados em conjunto possam ser alocados em um mesmo servidor, reduzindo a quantidade de comunicações entre servidores no processamento de suas consultas. Isto é essencial para prover escalabilidade e melhorar o desempenho de processamento das consultas em ambientes distribuídos. Os estudos experimentais mostram a melhoria no tempo de resposta das consultas utilizando a solução proposta.Abstract:Large volumes of data produced every day brought new challenges involving the definition of efficient ways to extract, store and access them. However, traditional database solutions are not efficient to solve these challenges, especially with respect to the scalability requirement. One approach to provide horizontal scalability to database management systems is the adoption of a layered architecture, based on a distributed storage system with a simple interface to access data remotely stored. This dissertation presents ALOCS, a distributed storage repository of data which adopts the key-value model, and which allows the allocation of a set of pairs grouped into a single structure whose location is controlled by the user application of the system. This control allows data commonly used together to be allocated on the same server, reducing the amount of communications between servers for query processing. This is essential to provide scalability and improve the processing of query execution in distributed environments. Experimental studies shows that ALOCS improves query response times by reducing the amount of remote data accesse