File Lookup Research Articles

Contact-Aware Dual-Layer CHORD for Peer-to-Peer Distribution in Integrated Satellite-Terrestrial Networks

Integrated satellite-terrestrial (IST) networks will play a promising role in future peer-to-peer (P2P) distribution by bridging multiple isolated P2P sub-networks to provide real-time cross-regional file access in certain scenarios. However, due to the periodic orbital movements of satellites, highly time-varying visibility among peer nodes in IST networks imposes significant challenge on file lookup and retrieval, which is difficult to be solved with current methods in terrestrial P2P networks. Therefore, in this paper, we propose a contact-aware dual-layer Chord (DL-Chord) lookup mechanism for P2P-based IST networks by carefully considering link contacts among satellites and terrestrial P2P nodes. In the proposed DL-Chord mechanism, we develop a group of novel algorithms, comprising an orbital parameter-based dual-layer identification mapping scheme, a contact-based dual-layer finger table, an efficient file lookup algorithm, and a node updating scheme. Furthermore, a theoretical analysis is conducted based on the visibility of satellite constellations to evaluate the lookup performance of the proposed DL-Chord mechanism, i.e., average lookup delay (ALD) and Average lookup rounds (ALR). Simulation results verify that the proposed mechanism achieves better efficiency in terms of ALD and ALR with a lower update cost than other similar schemes, i.e., the stochastic mapping-based original chord ring scheme (ORCO) and physical location-aware mapping-based wireless location-aware scheme (WILCO).

Finger Forwarding Scheme to Reduce Lookup Cost in Structured P2P Networks

Peer-to-peer (P2P) networks are distributed systems where each user shares his resources and cooperates with other users. These networks are designed over IP-based infrastructure. The resources of each user in these networks are shared in a distributed way on a trust based mechanism. P2P networks have some unique characteristics like scalability and cost efficiency, which separate these networks from other distributed networks. These networks are mainly used for resource sharing. However, resource searching in this type of networks is not centrally controlled in nature. Further poor search scalability is another limitation of these networks. Chord like or chord-based protocols used in the search operations in P2P networks utilize a finger table to shorten the query search length. We exploit the finger forwarding mechanism in our proposed scheme which further reduces the resource’s search path length. We propose a last finger search table in addition to finger table to enhance the file lookup performance in the structured P2P networks. The proposed scheme reduces the lookup path and increases search efficiency as compared to the existing chord and binary search routing equivalent schemes.

A Lightweight and Cooperative Multifactor Considered File Replication Method in Structured P2P Systems

File replication is widely used in structured P2P systems to avoid hot spots in servers and enhance file availability. The number of replicas and replication distance affect the file replication cost. These two elements and the replica update frequency determined in the file replication stage also affect the cost of subsequent consistency maintenance. However, most existing file replication protocols focus on improving file lookup efficiency without considering its cost and its subsequent influence on consistency maintenance. This paper studies the problem about how a server chooses files to replicate and where to replicate files to achieve low cost in both file replication and consistency maintenance stages without compromising the effectiveness of file replication. This paper presents a lightweight and Cooperative multifactOr considered file Replication Protocol (CORP) to achieve this goal. CORP simultaneously takes into account multiple factors including file popularity, update rate, node available capacity, file load, and node locality, aiming to minimize the number of replicas, update frequency, and replication distance. CORP also dynamically adjusts the number of replicas based on ever-changing file popularity and visit pattern. Extensive experimental results from simulation and PlanetLab real-world testbed demonstrate the efficiency and effectiveness of CORP in comparison with other file replication protocols. It dramatically reduces the overhead of both file replication and consistency maintenance. In addition, it exhibits high adaptiveness to skewed lookups and yields significant improvement in reducing overloaded nodes. Specifically, compared to the other replication protocols, CORP can reduce more than 71 percent of file replicas, 84 percent of overloaded nodes, 94 percent of consistency maintenance cost, and 72 percent of file replication and consistency maintenance latency.

NanoFS: a hardware‐oriented file system

NanoFS is a novel file system for embedded systems and storage-class memories (like flash) and is specially designed to be directly implemented in hardware. NanoFS is based on an original internal layout intended to achieve an optimal hardware implementation of the file system's file lookup and data fetch operations. File system specification on a sample reader module completely implemented in a programmable device is introduced.

Query routing mismatch alleviation architecture for P2P file lookup in MANETs

A cross-layer optimized query routing mismatch alleviation (QRMA) architecture is proposed to mitigate the problem of query routing mismatch (QRM) phenomenon between the structured peer to peer (P2P) overlay and the routing layer in mobile Ad-hoc networks (MANETs), which is an important issue that results in the inefficiency of lookup process in the system. Explicated with the representative Chord protocol, the proposal exploits the information of topologic neighbors in the routing layer of MANETs to find if there is any optimized alternative next hop in P2P overlay during conventional lookup progress. Once an alternative next hop is detected, it will take the shortcut to accelerate the query procedure and therefore alleviate the QRM problem in scalable MANETs without any assistance of affiliation equipments such as GPS device. The probability of finding out such an alternative node is formulated and the factors that could increase the chance are discussed. The simulation results show that the proposed architecture can effectively alleviate the QRM problem and significantly improve the system performance compared with the conventional mechanism.

HBA: Distributed Metadata Management for Large Cluster-Based Storage Systems

An efficient and distributed scheme for file mapping or file lookup is critical in decentralizing metadata management within a group of metadata servers. This paper presents a novel technique called Hierarchical Bloom Filter Arrays (HBA) to map filenames to the metadata servers holding their metadata. Two levels of probabilistic arrays, namely, the Bloom filter arrays with different levels of accuracies, are used on each metadata server. One array, with lower accuracy and representing the distribution of the entire metadata, trades accuracy for significantly reduced memory overhead, whereas the other array, with higher accuracy, caches partial distribution information and exploits the temporal locality of file access patterns. Both arrays are replicated to all metadata servers to support fast local lookups. We evaluate HBA through extensive trace-driven simulations and implementation in Linux. Simulation results show our HBA design to be highly effective and efficient in improving the performance and scalability of file systems in clusters with 1,000 to 10,000 nodes (or superclusters) and with the amount of data in the petabyte scale or higher. Our implementation indicates that HBA can reduce the metadata operation time of a single-metadata-server architecture by a factor of up to 43.9 when the system is configured with 16 metadata servers.