Analyzing locality over a P2P computing architecture

A characteristic of Peer-to-Peer (P2P) computing networks is their huge number of different computational resources scattered across the Internet. Gathering peers into markets according to their multi-attribute computational resources makes it easier to manage these environments. This solution is known as market overlay. In this context, the closeness of the markets with similar resources, known as locality, is a key feature for ensuring good P2P resource management. Thus, the locality feature over a market overlay allows a lack of resources in a given market to be compensated quickly by any other market with similar resources, whenever these are close to each other. Consequently, locality becomes an essential challenge.This paper addresses the analysis of the locality of P2P market over-lays. According to this, a new procedure for measuring locality is applied together with an extensive analysis of some well-known structured P2P overlays. Based on this analysis, a new P2P computing architecture, named DisCoP, oriented towards optimizing locality is proposed. Our proposal gathers the peers into markets according to their computational resources. A Hilbert function is used to arrange multi-attribute markets in an ordered and mono-dimensional space and the markets are linked by means of a Bruijn graph. In order to maintain the DisCoP locality whenever the overlay is not completed, a solution based on the virtualization of markets is also proposed. Finally, the DisCoP locality is tested together with the proposed virtualization method for approximate searches over uncompleted overlays. The simulation results show that approximate searches exploit the DisCoP locality efficiently.     

P2P资源搜索技术综述

对等(P2P)计算作为近年来兴起的一种重要的分布式计算模式,在很多领域都有着大量的应用和研究。随着越来越多的数据存储到P2P系统中,上层应用就需要底层架构来提供关键的数据定位和搜索能力,所以P2P资源搜索技术是P2P系统中的一种非常关键的技术,P2P资源搜索技术涉及到P2P系统的很多方面。例如资源定位所需要的时间,消耗的带宽等等。本文主要总结了当前P2P系统使用的几种重要的搜索技术以及相关应用,并对此进行总结,从而为研究P2P资源搜索提供思路和方法。     

利用结构化对等网络构造计算资源共享平台

设计和构建了一个基于结构化对等网络的计算资源共享平台DHT-CRSP。它可以把因特网上用户提交的科学计算作业高效地映射到平台中合适的工作节点上运行,通过容错和安全机制,能保证系统的可靠性和正确性。描述了DHT-CRSP中支持的两种分布式哈希表：Chord协议节点树和CAN协议空间区域;分析了DHT-CRSP中高效的资源匹配算法。通过构建评测环境,运行各种负载与作业场景下的结果表明,DHT-CRSP系统可以获得好的负载均衡性能、低的资源匹配代价,它提供了一种构建高性能的桌面网格平台的新思路。     

A novel state cache scheme in structured P2P systems

Large-scale P2P systems typically have hundreds of thousands of peers that involve frequent dynamic activities. Current structured overlays do not identify well the rhythm in the dynamic activities, thus resulting in high maintenance overhead. In this paper, we present a new state cache system, called SCS, that solves the problem by exploiting the access patterns of dynamic activities in P2P systems. SCS partitions the whole P2P network into clusters and dynamically chooses a “super” node in each cluster to selectively record and maintain the routing information for departed nodes most likely to arrive back in the near future. The cached routing information enables SCS to simplify self-organization, reduce system maintenance overhead and provide high quality routing service. The experimental results show that SCS reduces the maintenance overhead by up to 66% while delivering much better routing performance, as compared to current structured P2P systems.     

Grid和P2P混合环境中一种基于信任的资源搜索机制

Grid和P2P两种分布式计算模式中的资源搜索算法均假设节点提供可靠的资源,但Grid和P2P混合计算环境的动态、异构、自组织等特点使得一些节点存在冒名和提供虚假服务等行为。本文对基于经验和最好邻居搜索机制进行改进,引入信任因子,提出了基于信任的资源搜索机制。该机制有效抑制了欺骗行为,提高了资源搜索的可靠性和安全性。     

Toward a synergy between P2P and grids

Peer-to-peer (P2P) networks and grids are distributed computing models that enable decentralized collaboration by integrating computers into networks in which each can consume and offer services. P2P is a class of self-organizing systems or applications that takes advantage of distributed resources storage, processing, information, and human presence available at the Internet's edges. A grid is a geographically distributed computation platform comprising a set of heterogeneous machines that users can access through a single interface. Both are hot research topics because they offer promising paradigms for developing efficient distributed systems and applications. Unlike the classic client-server model, in which roles are well separated, P2P and grid networks can assign each node a client or server role according to the operations they are to perform on the network - even if some nodes act more as server than as client in current implementations. In spite of current practices and thoughts, the grid and P2P models share several features and have more in common than we perhaps generally recognize. It is time to consider how to integrate these two models. A synergy between the two research communities, and the two computing models, could start with identifying the similarities and differences between them.     

P2P data replication and trustworthiness for a JXTA-Overlay P2P system using fuzzy logic

P2P systems are very important for future distributed systems and applications. In such systems, the computational burden of the system can be distributed to peer nodes of the system. Therefore, in decentralized systems users become themselves actors by sharing, contributing and controlling the resources of the system. This characteristic makes P2P systems very interesting for the development of decentralized applications. Data replication techniques are commonplace in P2P systems. Data replication means storing copies of the same data at multiple peers thus improving availability and scalability. The trustworthiness of peers also is very important for safe communication in P2P system. The trustworthiness of a peer can be evaluated based on the reputation and actual behaviour of peers to provide services to other peers. In this paper, we propose two fuzzy-based systems for data replication and peer trustworthiness for JXTA-Overlay P2P platform. The simulation results have shown that in the first system, replication factor increases proportionally with increase of number of documents per peer, replication percentage and scale of replication per peer parameters and the second system can be used successfully to select the most reliable peer candidate to execute the tasks.     

一种基于K-means聚类分组的P2P超结点模型

本文面向网格计算、协同工作等特定P2P应用、提出了一种基于超节点的P2P混合网络模型。该模型的主要特点是采用K-means聚类算法对网络中的节点进行聚类,从而得到分组虚拟子网,由各子网内的超节点负责临近节点的加入与注销。该模型既克服P2P集中模型伸缩性不强,分散性P2P模型发送消息量大等缺点,又可以灵活地组织对等节点进行网格计算或组内协同工作等分布式应用。文章最后使用仿真实验表明K-means算法在网络节点聚类中的有效性。     

面向非结构化P2P 网络的双向随机漫步搜索机制

为解决目前Random Walk改进算法中过于依赖历史搜索记录而导致动态网络环境下搜索命中率低、网络开销过高和稀有资源的搜索成功率提高不明显等问题,通过分析随机漫步的基本性质和易转向高度数节点的搜索特性,提出了一种双向随机漫步搜索机制——BRWS(bidirectional random walk search),并证明了其能够提高包括稀有资源在内的搜索成功率,抗扰动性强.分别在静态和动态网络环境中,将Random Walk,APS(adaptive probabilistic search),PQR(path-traceable query routing),P2PBSN(peer-to-peer based on social network)和BRWS基于Random Graph、Scale Free网络、Small World网络3种拓扑进行了对比实验.结果表明,BRWS可以以较少的网络搜索代价,极大地提高搜索成功率;并在动态网络环境中,对稀有资源的搜索成功率也有显著提高.所提出的方法可适用于P2P文件分发网络应用中.     

Effectively utilizing global cluster memory for large data-intensive parallel programs

Large scientific parallel applications demand large amounts of memory space. Current parallel computing platforms schedule jobs without fully knowing their memory requirements. This leads to uneven memory allocation in which some nodes are overloaded. This, in turn, leads to disk paging, which is extremely expensive in the context of scientific parallel computing. To solve this problem, we propose a new peer-to-peer solution called parallel network RAM. This approach avoids the use of disk, better utilizes available RAM resources, and will allow larger problems to be solved while reducing the computational, communication, and synchronization overhead typically involved in parallel applications. We proposed several different parallel network RAM designs and evaluated the performance of each under different conditions. We discovered that different designs are appropriate in different situations.     

OHQFS:一种非结构化P2P网络中数据查询搜索新策略

为了提高非结构化P2P网络中数据查询搜索的效率,提出一种新型的一跳查询与转发数据搜索新策略（OHQFS）,它是以非结构化P2P网络中的数据查询请求转发策略和非转发策略为基础,将它们整合、集成后得到的一种新策略.OHQFS策略中的查询源结点直接搜索其自身的所有邻居节点,并将查询请求转发给这些邻居节点,使得这些邻居节点再去搜索它们的相邻节点.该策略在数据查询搜索过程中无须维持一个很大的邻居节点信息集合,系统维护开销较小,通过本策略中固有的一步查询转发,使其邻居节点和邻居的邻居节点处于查询搜索范围内.网络仿真的实验结果表明,OHQFS策略相对于转发搜索策略而言,它提高了查询效率;而相对于非转发策略,它获得了较高的成功率.     

Towards implementation of a novel scheme for data prefetching on distributed shared memory systems

High speed networks and rapidly improving microprocessor performance make the network of workstations an extremely important tool for parallel computing in order to speedup the execution of scientific applications. Shared memory is an attractive programming model for designing parallel and distributed applications, where the programmer can focus on algorithmic development rather than data partition and communication. Based on this important characteristic, the design of systems to provide the shared memory abstraction on physically distributed memory machines has been developed, known as Distributed Shared Memory (DSM). DSM is built using specific software to combine a number of computer hardware resources into one computing environment. Such an environment not only provides an easy way to execute parallel applications, but also combines available computational resources with the purpose of speeding up execution of these applications. DSM systems need to maintain data consistency in memory, which usually leads to communication overhead. Therefore, there exists a number of strategies that can be used to overcome this overhead issue and improve overall performance. Strategies as prefetching have been proven to show great performance in DSM systems, since they can reduce data access communication latencies from remote nodes. On the other hand, these strategies also transfer unnecessary prefetching pages to remote nodes. In this research paper, we focus on the access pattern during execution of a parallel application, and then analyze the data type and behavior of parallel applications. We propose an adaptive data classification scheme to improve prefetching strategy with the goal to improve overall performance. Adaptive data classification scheme classifies data according to the accessing sequence of pages, so that the home node uses past history access patterns of remote nodes to decide whether it needs to transfer related pages to remote nodes. From experimental results, we can observe that our proposed method can increase the accuracy of data access in effective prefetch strategy by reducing the number of page faults and misprefetching. Experimental results using our proposed classification scheme show a performance improvement of about 9–25% over the same benchmark applications running on top of an original JIAJIA DSM system.

A cross-layer approach for partition detection at overlay layer for structured P2P in MANETs

Due to limited radio range and mobility of nodes in mobile ad hoc networks (MANETs), the network partitioning and merging could occur frequently. When structured peer-to-peer (P2P) overlays are running over MANETs, then network partition in the physical network can also cause network partition at the overlay layer. Existing approaches for structured P2P overlay over MANETs do not detect network partition at the overlay layer. This paper proposes a cross-layer approach to detect network partition at the overlay layer for structured P2P overlay over MANETs. Simulation results show that the proposed approach is highly effective and efficient in terms of routing overhead, success ratio and false-negative ratio.     

非结构化P2P系统的Gnutella模型研究

对等(P2P)计算是未来网络是P2P网络实现的最为关键的问题.以Gnutella为例,研究了非结构化P2P系统近年来的搜索优化技术.根据现代Gnutella网络的特点,提出了一种有助于改进非结构化P2P系统扩展性的搜索机制.     

Scalable and topology-aware reconciliation on P2P networks

Collaborative applications are characterized by high levels of data sharing. Optimistic replication has been suggested as a mechanism to enable highly concurrent access to the shared data, whilst providing full application-defined consistency guarantees. Nowadays, there are a growing number of emerging cooperative applications adequate for Peer-to-Peer (P2P) networks. However, to enable the deployment of such applications in P2P networks, it is required a mechanism to deal with their high data sharing in dynamic, scalable and available way. Previous work on optimistic replication has mainly concentrated on centralized systems. Centralized approaches are inappropriate for a P2P setting due to their limited availability and vulnerability to failures and partitions from the network. In this paper, we focus on the design of a reconciliation algorithm designed to be deployed in large scale cooperative applications, such as P2P Wiki. The main contribution of this paper is a distributed reconciliation algorithm designed for P2P networks (P2P-reconciler). Other important contributions are: a basic cost model for computing communication costs in a DHT overlay network; a strategy for computing the cost of each reconciliation step taking into account the cost model; and an algorithm that dynamically selects the best nodes for each reconciliation step. Furthermore, since P2P networks are built independently of the underlying topology, which may cause high latencies and large overheads degrading performance, we also propose a topology-aware variant of our P2P-reconciler algorithm and show the important gains on using it. Our P2P-reconciler solution enables high levels of concurrency thanks to semantic reconciliation and yields high availability, excellent scalability, with acceptable performance and limited overhead.     

基于文件流行度的无结构P2P网络搜索机制

针对无结构P2P文件共享系统对不同流行度的文件使用相同的搜索策略从而导致大量网络资源的浪费问题,在研究Gnutella协议的基础上,提出一种基于LogLog算法的文件流行度判定机制,将它与Expanding Ring算法结合,给出一种基于流行度的搜索机制。与Expanding Ring相比,该搜索机制在一定程度上减少网络开销和响应时间,特别是稀缺文件的响应时间。     

Evaluation of P2P multimedia clustering techniques in JXTA-Overlay

Efficient file searching is an essential feature in P2P systems. While many current approaches use brute force techniques to search files by meta information (file names, extensions or user-provided tags), the interest is in implementing techniques that allow content-based search in P2P systems. Recently, clustering techniques have been used for searching text documents to increase the efficiency of document discovery and retrieval. Integrating such techniques into P2P systems is important to enhance searching in P2P file sharing systems. While some effort has been taken for content-based searching for text documents in P2P systems, there has been few research work for applying these techniques to multimedia content in P2P systems. In this paper, we introduce two P2P content-based clustering techniques for multimedia documents. These techniques are an adaptation of the existing Class-based Semantic Search algorithm for text documents. The proposed algorithms have been integrated into a JXTA-based Overlay P2P platform, and evaluation results are provided. The JXTA-Overlay together with the considered clustering techniques is thus very useful for developing P2P multimedia applications requiring efficient searching of multimedia contents in peer nodes.     

多核处理器并行计算模型研究

针对并行计算机体系结构中没有通用的计算模型这一问题,分析了一些现有的典型计算模型,在同步性、通信方式、参数方面进行比较,以LogGP模型为基础提出一种改进的mzLogGP模型。利用MPI并行算法对满足节点计算资源非独占、网络存在拥塞条件下的并行程序进行分析与测试,通过增加memory层次化层数和网络拥塞指数这两个参数,计算其计算开销和通信开销,将实测时间与预测时间进行比较,可知随节点数的增加系统误差不断减小,说明该新模型能改善并行应用在多核处理器集群平台上运行的性能,具有较好的可扩展性。     

基于路由学习的非结构化P2P搜索技术研究

针对无结构化P2P环境下P2P泛洪搜索的盲目性和高资源消耗性,提出一个基于路由学习的非结构化P2P搜索算法,建立两个索引表,存储三类节点信息,通过学习关联节点的信息,建立路由表,并定时与路由表内节点交换信息,减少搜索时间,降低搜索开销。理论和仿真实验证明该算法能有效地提高搜索速度,降低搜索开销。     

具有社会网络特性的P2P分层搜索机制

无结构P2P网络中基于泛洪法的搜索机制会给系统带来极大的网络负载,结构化P2P网络则需要较大的开销来维护其拓扑结构。针对该问题,给出一种具有社会网络特性的P2P分层搜索机制。根据社会网络的基本原理,将语义相似度高的节点分布在同一个虚拟社区,节点在虚拟社区内能动地建立搜索链接。实验结果证明,该搜索机制能有效地提高P2P网络的资源搜索效率。