PATCOM:基于分割树的无结构P2P系统一致性维护方法

无结构P2P技术逐渐被应用在新型的协同计算系统中.这些新型业务支持数据的动态更新,不仅要求副本数据的强一致性,而且要求更新数据的快速传播.高效的一致性维护方法是保证新业务顺利开展的基础.在比较分析现有的P2P系统一致性维护方法的基础上,针对无结构P2P系统,提出了一种基于分割树的一致性维护方法--PATCOM.PATCOM使用Chord协议作为组管理协议,通过不断分割由副本节点组成的Chord环,动态地建立更新消息传播树(Update Message Propagation Tree,UMPT).论文进一步从理论上分析了UMPT的平均高度、PATCOM的性能、容错能力以及算法开销,并和基于Gossip的一致性维护方法进行了比较.理论分析和仿真实验结果表明:PATCOM不仅能够快速地维护P2P系统的强一致性,而且产生的冗余更新消息少.     

IRM: Integrated File Replication and Consistency Maintenance in P2P Systems

In peer-to-peer file sharing systems, file replication and consistency maintenance are widely used techniques for high system performance. Despite significant interdependencies between them, these two issues are typically addressed separately. Most file replication methods rigidly specify replica nodes, leading to low replica utilization, unnecessary replicas and hence extra consistency maintenance overhead. Most consistency maintenance methods propagate update messages based on message spreading or a structure without considering file replication dynamism, leading to inefficient file update and hence high possibility of outdated file response. This paper presents an Integrated file Replication and consistency Maintenance mechanism (IRM) that integrates the two techniques in a systematic and harmonized manner. It achieves high efficiency in file replication and consistency maintenance at a significantly low cost. Instead of passively accepting replicas and updates, each node determines file replication and update polling by dynamically adapting to time-varying file query and update rates, which avoids unnecessary file replications and updates. Simulation results demonstrate the effectiveness of IRM in comparison with other approaches. It dramatically reduces overhead and yields significant improvements on the efficiency of both file replication and consistency maintenance approaches.     

A proactive low-overhead file replication scheme for structured P2P content delivery networks

File replication is a widely used technique for high performance in peer-to-peer content delivery networks. A file replication technique should be efficient and at the same time facilitates efficient file consistency maintenance. However, most traditional methods do not consider nodes’ available capacity and physical location in file replication, leading to high overhead for both file replication and consistency maintenance. This paper presents a proactive low-overhead file replication scheme, namely Plover. By making file replicas among physically close nodes based on nodes’ available capacities, Plover not only achieves high efficiency in file replication but also supports low-cost and timely consistency maintenance. It also includes an efficient file query redirection algorithm for load balancing between replica nodes. Theoretical analysis and simulation results demonstrate the effectiveness of Plover in comparison with other file replication schemes. It dramatically reduces the overhead of both file replication and consistency maintenance compared to other schemes. In addition, it yields significant improvements in reduction of overloaded nodes.     

An optimized strategy for update path selection in unstructured P2P networks

With the growth of P2P file sharing systems, people are no longer satisfied with the sharing of the read-only and static files, and thus the systems with mutually writable and dynamic files have emerged, resulting in the replica inconsistency problem. To maintain the replica consistency, too many update messages need to be redundantly propagated due to the lack of the sharing of globally updated path information in the existing strategies. To address this problem, we propose an optimized strategy for update path selection, which makes the nodes share the update path information by using clone, variation and crossover operations for the update paths. We also present a repeated update strategy to cope with the churn problem so as to maintain replica consistency as far as possible even if some nodes temporarily leave the network. The simulation results show that our strategy can significantly reduce the number of the redundant update messages without lowering the message coverage, thus improving the availability of the unstructured P2P networks.     

P2P存储系统副本一致性维护策略

副本策略是提高P2P存储系统的可扩展性、容错性、可用性的有效手段。随着新的应用发展,P2P中副本应用从只读静态文件共享转变为读写动态文件交互,副本的一致性维护变得越来越重要。提出一种副本信息传播树的维护策略,该策略把文件副本的相关信息保存在二叉树上,通过订阅和取消订阅算法维护副本的一致。实验证明该策略能有效减少维护开销,避免相关问题的出现。     

Enabling dynamic file I/O path selection at runtime for parallel file system

Parallel file systems are experiencing more and more applications from various fields. Various applications have different I/O workload characteristics, which have diverse requirements on accessing storage resources. However, parallel file systems often adopt the “one-size-fits-all” solution, which fails to meet specific application needs and hinders the full exploitation of potential performance. This paper presents a framework to enable dynamic file I/O path selection with fine granularity at runtime. The framework adopts a file handle-rich scheme to allow file systems choose corresponding optimizations to serve I/O requests. Consistency control algorithms are proposed to ensure data consistency while changing optimizations at runtime. One case study on our prototype shows that choosing proper optimizations can improve the I/O performance for small files and large files by up to 40 and 64.4 %, respectively. Another case study shows that the data prefetch performance for real-world application traces can be improved by up to 193 % by selecting correct prefetch patterns. Simulations in large-scale environment also show that our method is scalable and both the memory consumption and the consistency control overhead can be negligible.     

基于混合策略的低成本云存储方案

为了保证云存储系统数据的高可用性、降低数据存储成本和带宽成本、缩短数据对象的访问时间,提出一种称为缓存大小自适应确定(CAROM)的新方案。CAROM结合传统的基于缓存策略的方法和纠错码方法来提高云文件系统的弹性和效率。另外,为了在缓存大小及其效益间实现平衡,提出一种基于总体成本凸函数特性的自适应方法来实现缓存大小的自适应选择。在基于现实世界文件系统数据的性能评估中,CAROM方案的存储成本和带宽成本分别比复制策略和纠错码策略下降60%和43%,同时访问延时与复制策略相当。结果表明,CAROM方案在支持当前云文件系统语义一致性的同时,兼具带宽成本低、存储成本低和访问成本低等特性。     

基于纠删编码P2P存储系统的数据维护算法

纠删编码是一种通过产生数据冗余来提高P2P存储系统容错性和可用性的有效方法。对基于纠删编码的非结构化P2P存储系统来说,使用洪泛算法进行数据维护会在网络中产生大量冗余消息,系统效率低。本文提出一种使用二叉树来保存文件块的信息的算法。二叉树结构被建立以后,更新消息在二叉树中的节点间传播,不需要在网络中洪泛。分析表明,相较于洪泛算法,本算法有效减少了冗余的消息数量,提高了数据维护的效率,而付出的是极小的存储代价。     

H-Trust: A Group Trust Management System for Peer-to-Peer Desktop Grid

Peer-to-Peer Desktop Grid (P2PDG) has emerged as a pervasive cyber-infrastructure tackling many large-scale applications with high impacts. As a burgeoning research area, P2PDG can support numerous applications, including scientific computing, file sharing, web services, and virtual organization for collaborative activities and projects. To handle trustworthiness issues of these services, trust and reputation schemes are proposed to establish trust among peers in P2PDG. In this paper, we propose a robust group trust management system, called H-Trust, inspired by the H-index aggregation technique. Leveraging the robustness of the H-index algorithm under incomplete and uncertain circumstances, H-Trust offers a robust personalized reputation evaluation mechanism for both individual and group trusts with minimal communication and computation overheads. We present the H-Trust scheme in five phases, including trust recording, local trust evaluation, trust query phase, spatial-temporal update phase, and group reputation evaluation phases. The rationale for its design, the analysis of the algorithm are further investigated. To validate the performance of H-Trust scheme, we designed the H-Trust simulator HTrust-Sim to conduct multi-agent-based simulations. Simulation results demonstrate that H-Trust is robust and can identify and isolate malicious peers in large scale systems even when a large portion of peers are malicious.     

P2P系统中基于副本链的一致性维护算法

提出一种无结构纯P2P的副本一致性维护算法。利用副本节点发起的第一次更新消息在P2P网络中的广播,由其他收到消息的副本节点给出响应,构建副本链。副本链建立后,更新消息在副本节点间进行传播,不再在网络中洪泛。副本链的维护通过记录首次发起更新的副本节点IP地址完成。仿真试验证明该算法是简单有效的。     

选择性传输协议的实现及在DVE中的应用

在分布式虚拟环境中,为了提供高水平的通信服务,需要灵活高效的传输协议。分布式虚拟环境中传输的消息可以分为两类:大量的场景更新信息,这种消息需要保证实时性;相对较少的控制信息,这种消息传输强调可靠性。为满足分布式虚拟环境中消息传输的不同需求,这里实现了一种新的传输协议——选择性传输协议,并将其成功地应用于笔者实现的一个分布式虚拟环境平台CADRTI。该协议提供了有效的重传缓存管理,避免了确认信息爆炸,还可以有效减少系统通信开销及缓解网络拥塞。     

基于P2P的数字证书撤销列表更新方案及性能分析

针对数字证书撤销列表更新中大量结点同时请求数据造成的系统性能瓶颈,本文提出了基于P2P的数字证书撤销列表更新方案,利用客户结点的资源改善证书撤销列表的更新性能;以数字校园应用为背景建立了分析模型,对所提方案进行了分析比较。     

A performance comparison of mobility anchor point selection schemes in Hierarchical Mobile IPv6 networks

Hierarchical Mobile IPv6 (HMIPv6) introduces a mobility anchor point (MAP) that localizes the signaling traffic and hence reduces the handoff latency. In addition to processing binding update messages from mobile nodes (MNs) on behalf of MNs’ home agents (HAs), the MAP performs data traffic tunneling destined to or originated from MNs, both of which will burden the MAP substantially as the network size grows. To provide scalable and robust mobile Internet services to a large number of visiting MNs, multiple MAPs will be deployed. In such an environment, how to select an appropriate MAP has a vital effect on the overall network performance. In this paper, we choose four MAP selection schemes: the furthest MAP selection scheme, the nearest MAP selection scheme, the mobility-based MAP selection scheme, and the adaptive MAP selection scheme. Then, we compare their performances quantitatively in terms of signaling overhead and load balancing. It can be shown that the dynamic schemes (i.e., the mobility-based and the adaptive MAP selection schemes) are better than the static schemes (i.e., the furthest and the nearest MAP selection schemes), since the dynamic schemes can select the serving MAP depending on the MN’s characteristics, e.g., mobility and session activity. In addition, the adaptive MAP selection scheme achieves low implementation overhead and better load balancing compared with the mobility-based MAP selection scheme.     

FLEXIBLE FUZZY PRIORITY SCHEDULING OF THE CAN BUS

With the increasing complexity of distributed real‐time systems, the need for improved CAN bus performance is continually increasing. Normally, a scheduling scheme with static‐priority has low network schedulability/utilization; while using dynamic priority will improve the QoS of the network at the cost of a narrow service range or a high overhead, compared with the fixed priority scheduling schemes. Actually, because of the fluctuation of network traffic, these priority policies may not guarantee flexibility for different kinds of messages. Based on the broadcast nature of the CAN bus, a closed‐loop fuzzy scheduling scheme is proposed in this paper. Compared with the dynamic priority schemes, this fuzzy scheduling scheme uses fewer bits to encode fewer priority levels, which widens the service range of the network without increasing overhead. Based on game theory, a fuzzy parameter updating algorithm for the fuzzy scheme is developed to improve the adaptation of the scheme, which guarantees the required QoS of the network even with traffic fluctuation. Simulation results well demonstrate the abilities of the fuzzy scheme to guarantee high schedulability for real‐time messages, as well as the fairness and the same QoS for non‐real‐time messages in networks.     

From Centralized Workflow Specification to Distributed Workflow Execution

Current workflow management systems fall short of supporting large-scale distributed, enterprise-wide applications. We present a scalable, rigorously founded approach to enterprise-wide workflow management, based on the distributed execution of state and activity charts. By exploiting the formal semantics of state and activity charts, we develop an algorithm for transforming a centralized state and activity chart into a provably equivalent partitioned one, suitable for distributed execution. A synchronization scheme is developed that guarantees an execution equivalent to a non-distributed one. This basic solution is further refined in order to reduce communication overhead and exploit parallelism between partitions whenever possible. The developed synchronization schemes are compared in terms of the number and size of synchronization messages.     

基于DHT的P2P系统负载均衡的有效算法

基于DHT的P2P系统中,各种因素例如结点异构性和不同的文件访问率等,都可能会影响DHT系统的效率。本文提出一个基于DHT的P2P系统中有效的负载均衡算法。该算法提出一个全分布机制来维护文件访问的历史信息,用来预测未来文件访问频率。设计了一个新的负载均衡算法,当新结点加入时,历史信息和结点异构性一起用来决定最佳负载分配。在系统运行期间如果有过载结点出现也可动态执行负载重分配。该算法不使用虚服务器,减少了维护路由元数据的处理开销。     

网格环境下的数据副本一致性维护解决方案

副本技术是网格中提高数据访问和处理效率的关键技术。针对目前副本管理存在的局限性和亟待解决的一致性维护关键问题,以Globus提供的副本技术为基础,从副本创建与更新的角度出发,采用日志管理思想,提出了一种副本创建与一致性维护相结合的解决方案。     

Efficient and Scalable Consistency Maintenance for Heterogeneous Peer-to-Peer Systems

Consistency maintenance mechanism is necessary for the emerging Peer-to-Peer applications due to their frequent data updates. Centralized approaches suffer single point of failure, while previous decentralized approaches incur too many duplicate update messages because of locality-ignorant structures. To address this issue, we propose a scalable and efficient consistency maintenance scheme for heterogeneous P2P systems. Our scheme takes the heterogeneity nature into account and forms the replica nodes of a key into a locality-aware hierarchical structure, in which the upper layer is DHT-based and consists of powerful and stable replica nodes, while a replica node at the lower layer attaches to a physically close upper layer node. A d-ary update message propagation tree (UMPT) is dynamically built upon the upper layer for propagating the updated contents. As a result, the tree structure does not need to be maintained all the time, sav-ing a lot of cost. Through theoretical analyses and comprehensive simulations, we examine the efficiency and scalability of this design. The results show that, compared with previous designs, especially locality-ignorant ones, our approach is able to reduce the cost by about 25-67 percent.     

基于蚁群优化算法的纠删码存储系统数据更新方案

由于纠删码具备高可用性和高存储空间有效性的特点,采用纠删码为大规模分布式存储系统提供数据持久性已成为事实标准然而,纠删码的密集型更新操作将导致大量的数据传输和I/O开销.如何减少数据传输量,优化现有网络资源的利用率,以提高纠删码的更新效率,成为纠删码存储系统面临的重要挑战.然而,在多重服务质量(quality of s...     

面向Android系统的目录自适应日志模式选择机制

在写磁盘的过程中如果意外掉电或系统崩溃很有可能导致文件系统中用户数据和元数据不一致,现有文件系统主要采取写前日志或写时拷贝等一致性技术来解决该问题,但均没有考虑目录对可靠性需求的差异性。针对现有的文件自适应日志模式存在的需要逐一修改应用程序的不足,提出了面向Android系统的目录自适应的日志模式选择机制,即针对不同的目录对可靠性需求的高低等级,选择相应的强弱程度不同的日志模式,同时分配可靠性不同的存储区域,这种机制对开发者完全透明,也符合Android系统的应用特征,在可靠性需求不变的前提下最大限度地减少了一致性保证引入的额外开销。实验结果表明,修改后的文件系统可以识别文件所在目录,并根据目录选择预先定义的日志模式。