116 research outputs found
Data Currency in Replicated DHTs
International audienceDistributed Hash Tables (DHTs) provide a scalable solution for data sharing in P2P systems. To ensure high data availability, DHTs typically rely on data replication, yet without data currency guarantees. Supporting data currency in replicated DHTs is difficult as it requires the ability to return a current replica despite peers leaving the network or concurrent updates. In this paper, we give a complete solution to this problem. We propose an Update Management Service (UMS) to deal with data availability and efficient retrieval of current replicas based on timestamping. For generating timestamps, we propose a Key-based Timestamping Service (KTS) which performs distributed timestamp generation using local counters. Through probabilistic analysis, we compute the expected number of replicas which UMS must retrieve for finding a current replica. Except for the cases where the availability of current replicas is very low, the expected number of retrieved replicas is typically small, e.g. if at least 35% of available replicas are current then the expected number of retrieved replicas is less than 3. We validated our solution through implementation and experimentation over a 64-node cluster and evaluated its scalability through simulation up to 10,000 peers using SimJava. The results show the effectiveness of our solution. They also show that our algorithm used in UMS achieves major performance gains, in terms of response time and communication cost, compared with a baseline algorithm
Currency management system: a distributed banking service for the grid
Market based resource allocation mechanisms require mechanisms to regulate and manage the usage of traded resources. One mechanism to control this is the definition of some kind of currency. Within this context, we have implemented a first prototype of our Currency Management System, which stands for a decentralized and scalable banking service for the Grid. Basically, our system stores user accounts within a DHT and its basic operation is the transferFunds which, as its name suggests, transfers virtual currency from an account to one another
Efficient Processing of Continuous Join Queries using Distributed Hash Tables
International audienceThis paper addresses the problem of computing approximate answers to continuous join queries. We present a new method, called DHTJoin, which combines hash-based placement of tuples in a Distributed Hash Table (DHT) and dissemination of queries using a gossip style protocol. We provide a performance evaluation of DHTJoin which shows that DHTJoin can achieve significant performance gains in terms of network traffic
Crux: Locality-Preserving Distributed Services
Distributed systems achieve scalability by distributing load across many
machines, but wide-area deployments can introduce worst-case response latencies
proportional to the network's diameter. Crux is a general framework to build
locality-preserving distributed systems, by transforming an existing scalable
distributed algorithm A into a new locality-preserving algorithm ALP, which
guarantees for any two clients u and v interacting via ALP that their
interactions exhibit worst-case response latencies proportional to the network
latency between u and v. Crux builds on compact-routing theory, but generalizes
these techniques beyond routing applications. Crux provides weak and strong
consistency flavors, and shows latency improvements for localized interactions
in both cases, specifically up to several orders of magnitude for
weakly-consistent Crux (from roughly 900ms to 1ms). We deployed on PlanetLab
locality-preserving versions of a Memcached distributed cache, a Bamboo
distributed hash table, and a Redis publish/subscribe. Our results indicate
that Crux is effective and applicable to a variety of existing distributed
algorithms.Comment: 11 figure
Optimising Structured P2P Networks for Complex Queries
With network enabled consumer devices becoming increasingly popular, the number of connected devices and available services is growing considerably - with the number of connected devices es- timated to surpass 15 billion devices by 2015. In this increasingly large and dynamic environment it is important that users have a comprehensive, yet efficient, mechanism to discover services.
Many existing wide-area service discovery mechanisms are centralised and do not scale to large numbers of users. Additionally, centralised services suffer from issues such as a single point of failure, high maintenance costs, and difficulty of management. As such, this Thesis seeks a Peer to Peer (P2P) approach.
Distributed Hash Tables (DHTs) are well known for their high scalability, financially low barrier of entry, and ability to self manage. They can be used to provide not just a platform on which peers can offer and consume services, but also as a means for users to discover such services.
Traditionally DHTs provide a distributed key-value store, with no search functionality. In recent years many P2P systems have been proposed providing support for a sub-set of complex query types, such as keyword search, range queries, and semantic search.
This Thesis presents a novel algorithm for performing any type of complex query, from keyword search, to complex regular expressions, to full-text search, over any structured P2P overlay. This is achieved by efficiently broadcasting the search query, allowing each peer to process the query locally, and then efficiently routing responses back to the originating peer. Through experimentation, this technique is shown to be successful when the network is stable, however performance degrades under high levels of network churn.
To address the issue of network churn, this Thesis proposes a number of enhancements which can be made to existing P2P overlays in order to improve the performance of both the existing DHT and the proposed algorithm. Through two case studies these enhancements are shown to improve not only the performance of the proposed algorithm under churn, but also the performance of traditional lookup operations in these networks
IPFS as a foundation for anonymous file storage
The intention of the work is to evaluate IPFS as a technology, and place it within the contextbof the state of the art in terms of distributed systems. Once this is done, evaluate the design
of a file storage service, but relying on the decentralization capabilities offered by IPFS,badding anonymity capabilities for users and their data.La intenció del treball és avaluar IPFS com a tecnologia, i situar-lo dins del context de l'estat de l'art quant a sistemes distribuïts. Un cop fet això, plantejar el disseny d'un servei
d'emmagatzematge de fitxers, però que es recolzi en les capacitats de descentralització que ofereix IPFS, afegint capacitats d'anonimat per als usuaris i les seves dades.La intención del trabajo es evaluar IPFS como tecnologÃa, y situarlo dentro del contexto del estado del arte en cuanto a sistemas distribuidos. Una vez hecha esto, plantear el diseño de un servicio de almacenamiento de ficheros, pero que se apoye en las capacidades de descentralización que ofrece IPFS, añadiendo capacidades de anonimato para los usuarios y sus datos
LightChain: A DHT-based Blockchain for Resource Constrained Environments
As an append-only distributed database, blockchain is utilized in a vast
variety of applications including the cryptocurrency and Internet-of-Things
(IoT). The existing blockchain solutions have downsides in communication and
storage efficiency, convergence to centralization, and consistency problems. In
this paper, we propose LightChain, which is the first blockchain architecture
that operates over a Distributed Hash Table (DHT) of participating peers.
LightChain is a permissionless blockchain that provides addressable blocks and
transactions within the network, which makes them efficiently accessible by all
the peers. Each block and transaction is replicated within the DHT of peers and
is retrieved in an on-demand manner. Hence, peers in LightChain are not
required to retrieve or keep the entire blockchain. LightChain is fair as all
of the participating peers have a uniform chance of being involved in the
consensus regardless of their influence such as hashing power or stake.
LightChain provides a deterministic fork-resolving strategy as well as a
blacklisting mechanism, and it is secure against colluding adversarial peers
attacking the availability and integrity of the system. We provide mathematical
analysis and experimental results on scenarios involving 10K nodes to
demonstrate the security and fairness of LightChain. As we experimentally show
in this paper, compared to the mainstream blockchains like Bitcoin and
Ethereum, LightChain requires around 66 times less per node storage, and is
around 380 times faster on bootstrapping a new node to the system, while each
LightChain node is rewarded equally likely for participating in the protocol
Peer-to-Peer Networks and Computation: Current Trends and Future Perspectives
This research papers examines the state-of-the-art in the area of P2P networks/computation. It attempts to identify the challenges that confront the community of P2P researchers and developers, which need to be addressed before the potential of P2P-based systems, can be effectively realized beyond content distribution and file-sharing applications to build real-world, intelligent and commercial software systems. Future perspectives and some thoughts on the evolution of P2P-based systems are also provided
XtreemOS application execution management: a scalable approach
Designing a job management system for the Grid is a non-trivial task. While a complex middleware can give a lot of features, it often implies sacrificing performance. Such
performance loss is especially noticeable for small jobs. A Job Manager’s design also affects the capabilities of the monitoring
system. We believe that monitoring a job or asking for a job status should be fast and easy, like doing a simple ’ps’. In this paper, we present the job management of XtreemOS - a Linux-based operating system to support Virtual Organizations for Grid. This management is performed inside the Application Execution Manager (AEM). We evaluate its performance using only one job manager plus the built-in monitoring infrastructure. Furthermore, we present a set of real-world applications using AEM and its features. In XtreemOS we avoid reinventing the wheel and use the Linux paradigm as an abstraction.Peer ReviewedPostprint (published version
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