Proportional Replication in Peer-to-Peer Networks

2006

The peer-to-peer (P2P) architecture provides support for the next generation of information sharing applications. A difficult challenge faced by these systems in the presence of non-uniform data distribution and dynamic network conditions is load sharing. This paper addresses the problem of load sharing in P2P networks across heterogeneous super-peers. We propose two load sharing techniques that use data replication to improve access performance. In the first technique, called Periodic Push-based Replication (PPR), super-peers periodically send replicas of the most frequently accessed files to remote super-peers. This effectively reduces the hop count to fetch these files. The second technique, called On-Demand Replication (ODR), performs replication based on access frequency. By performing replication on-demand, ODR provides adaptability to changes in access behavior. Extensive testing have been conducted to study the performance of the proposed techniques. The results obtained demonstrate significant performance improvements through replication.

Peer-to-peer storage systems organize a collection of symmetric nodes to store data without the use of centralized data structures or operations. As a result, they can scale to many thousands of nodes and can be formed directly by clients. This paper describes the design and implementation Mammoth, which implements a traditional UNIX-like hierarchical file system in a peer-to-peer fashion. Each Mammoth node stores a potentially arbitrary collection of directories and files that may be replicated on multiple nodes. The only thing that links these nodes together is that each metadata object encodes the network addresses of the nodes that store it. Data is replicated by a background process whose operation is simplified by the fact that files are stored as journals of immutable versions. An optimistic replication technique is used to allow nodes to read and write whatever version of data they can access, while also ensuring consistency when nodes are connected. In the event of temporary failure, eventual consistency is achieved by ensuring that every replica of a directory or file metadata object receives all updates to the object, irrespective of delivery order. While an update is being propagated every node that receives it cooperates to ensure that the update is delivered, even if the original sender fails. Our prototype is implemented as a user-level NFS server. Its performance is comparable to a standard NFS server and it will be publicly available soon.

Proceedings of the International Conference on Dependable Systems and Networks, 2006

Peer-to-peer systems provide the opportunity to pool large amounts of distributed resources to enable internetscale applications. However, the participant nodes are highly dynamic and unreliable. Thus, any shared resource such as file objects must incorporate redundancy to be useful. While many studies have proposed heuristics to determine redundancy levels based on object popularity, there has been little work in determining optimal or near-optimal resource allocation based on node reliability. In this paper, we present a strategy for the allocation of objects in the presence of dynamic and unreliable peers. We have built an availability model of peer-to-peer storage systems based on the bimodal and time-dependent availability characteristics of a P2P node. Using this model, we can select the size of a candidate node set for storage allocation and assign storage objects to maximize availability while still maintaining a balanced distribution of objects.

2013 International Conference on Parallel and Distributed Systems, 2013

This paper addresses the problem of maintaining replicated data in large scale P2P systems. Although this topic has been extensively studied in the literature, to maintain replicated data in this setting, in an efficient manner, still remains a significant challenge. This paper proposes novel policies to address this problem and evaluates their performance against different criteria, such as monitoring costs, data transfer costs, and load unbalance costs. We show that one of these new policies significantly outperforms previous work. Interestingly, this policy is based on a somehow counter-intuitive approach, that uses less reliable nodes to store the most accessed data items. The insights to derive this policy were obtained from an in depth analysis of existing solutions, that is also captured in the paper.

Pdpta, 2009

The paper 1 focuses on distributed file systems in P2P networks. We introduce a novel file replication scheme which is adaptive, reacting to changes in the patterns of access to the file system by dynamically creating or deleting replicas. Replication is used to increase data availability in the presence of site or communication failures and to decrease retrieval costs by local access if possible. Our system is completely decentralized and nodes can be removed/added dynamically. We also propose an overlay architecture for file search. This architecture is structured, but also based on random walk. Our system has a mobile agent which performs dynamic load-balancing. This agent is event driven and circulates in the network to find and "destroy" the least important files and thus limit the proliferation of superfluous replicas. We have implemented our method at TCP/IP sockets level.

2004

Peer-to-peer file sharing applications have become increasingly popular. Measurements of P2P systems indicate large heterogeneity in the availability of individual nodes. Many have cyclic behavior, whereas others are always available. This paper proposes a cooperative storage technique which employs erasure coding schemes on a collection of data objects and provides various levels of data redundancy. Based on this technique, we study a historybased hill climbing scheme that takes advantage of varied time zones in a global p2p system. Our simulation results show the improved data availability by this scheme. We also investigate several climbing strategies including choice of coding schemes and laziness of data movement.

Peer-to-peer (P2P) technology is an emerging approach to overcoming the limitations of the traditional client server architecture. However, building a highly available P2P system is quite challenging, in particular a P2P storage system. The reason is due to the fundamental nature of P2P systems: peers can join and leave at any time without any notice. Replication is one of the strategies in overcoming the unpredictable behavior of peers. A good replication algorithm should use the minimum number of replicas to provide the desired availability of data. The popular approach in the previous studies is a random placement of replicas, but it ignores the wide difference in the availability of each peer. In this paper, we propose PAT (Peer Availability in order to analyze and predict the state of nodes and develop a replica placement algorithm, which exploits the availability pattern of each individual peer. By comparing our algorithm with a random placement scheme, we show that our algorithm dramatically improves the data availability with moderate overhead in terms of memory consumption and processing time in both ideal and practical conditions. Additionally, we demonstrate the application of PAT as an analysis tool for various P2P systems.

IEEE Transactions on Parallel and Distributed Systems, 2000

Distributed peer-to-peer systems rely on voluntary participation of peers to effectively manage a storage pool. In such systems, data is generally replicated for performance and availability. If the storage associated with replication is not monitored and provisioned, the underlying benefits may not be realized. Resource constraints, performance scalability, and availability present diverse considerations. Availability and performance scalability, in terms of response time, are improved by aggressive replication, whereas resource constraints limit total storage in the network. Identification and elimination of redundant data pose fundamental problems for such systems. In this paper, we present a novel and efficient solution that addresses availability and scalability with respect to management of redundant data. Specifically, we address the problem of duplicate elimination in the context of systems connected over an unstructured peer-to-peer network in which there is no a priori binding between an object and its location. We propose two randomized protocols to solve this problem in a scalable and decentralized fashion that does not compromise availability requirements of the application. Performance results using both largescale simulations, and a prototype built on PlanetLab, demonstrate that our protocols provide high probabilistic guarantees, while incurring minimal administrative overheads.

2006

We present APRE, a replication method for structureless Peer-to-Peer overlays. The goal of our method is to achieve real-time replication of even the most sparsely located content relative to demand. APRE adaptively expands or contracts the replica set of an object in order to improve the sharing process and achieve a low load distribution among the providers. To achieve that, it utilizes search knowledge to identify possible replication targets inside query-intensive areas of the overlay. We present detailed simulation results where APRE exhibits both efficiency and robustness relative to the number of requesters and the respective request rates. The scheme proves particularly useful in the event of flash crowds, managing to quickly adapt to sudden surges in load.