Version Vectors Research Articles

OWebSync: Seamless Synchronization of Distributed Web Clients

Many enterprise software services are adopting a fully web-based architecture for both internal line-of-business applications and for online customer-facing applications. Although wireless connections are becoming more ubiquitous and faster, mobile employees and customers are often offline due to expected or unexpected network disruptions. Nevertheless, continuous operation of the software is expected. This article presents OWebSync: a web-based middleware for data synchronization in interactive groupware with fast resynchronization of offline clients and continuous, interactive synchronization of online clients. To automatically resolve conflicts, OWebSync implements a fine-grained data synchronization model and leverages state-based Conflict-free Replicated Data Types. This middleware uses Merkle-trees embedded in the tree-structured data and virtual Merkle-tree levels to achieve the required interactive performance. Our comparative evaluation with available operation-based and delta-state-based middleware solutions shows that OWebSync is especially better in operating in and recovering from offline settings and network disruptions. In addition, OWebSync scales more efficiently over time, as it does not store version vectors or other meta-data for all past clients.

Version-vector based video data online cloud backup in smart campus

As a kind of popular multimedia service, the video business in smart campus is fully developed, and the data volume is experiencing a continuous tremendous growth. However, the video data storage also needs to cope with many security threats resulted from some uncertainly factors. Recently, data backup has been credited as an important method to address these issues. Yet, how to improve the efficiency of video data online backup remains a critical challenge. In the context of cloud computing, a version-vector based video data online backup system is proposed in this paper, which fully implements three important functions, e.g., backup, indexing and recovery. At the time of the client backuping the data to the server, the version vectors of files and data chunks are produced as metadata. Accordingly, only through exchanging a small amount of metadata between the data nodes, it can identify the redundant data such that breaking the limitations on file-level deduplication and data-chunk-level deduplication in the existing backup systems, and can further improve the performance of backup, indexing and recovery. The conducted experiments have been shown to demonstrate the efficiency.

Engineering change information propagation in aviation industrial manufacturing execution processes

Engineering change (EC) is common in the aviation industry, which affects the production efficiency and the stability of a manufacturing system as a frequent disturbance. The way how to respond to EC in manufacturing execution processes is one of the most important and complex issue in manufacturing industries. And the prime step for manufacturing department to accomplish EC efficiently is to detect and identify changes correctly and in time. According to special features of the aviation industry, engineering bill of material (EBOM) and manufacturing BOM (MBOM) models are proposed to save EC information accurately and timely by using version vectors to record version information. EC may affect the production process directly by those changed items, but it can make a potential impact on some related items. The EC propagation mechanism is described to collect all the items impacted by EC. The method of Tree-Root tracking and the ripple strategy of expand searching with capacity restriction are explained by a composite material manufacturing case. It figures out the range of impact of EC which may help to point out what, where, and when need to rearrange the schedule in order to optimizing the implement of EC especially after manufacturing commences. The approach was proved to be practical with a case of aviation carbon fiber composite material components.

Formula omitted] version vector: Logging version vectors concisely in dynamic replication

In a replication system, version vectors are logged with replicas to detect conflicts among operations. Dynamic replications where replicas are frequently created and destroyed suffer from expensive logging overhead caused by inactive entries of version vectors. Although the rigmarole of pruning vectors can delete inactive entries, the vectors may be incompatible without additional information, which also causes another overhead. This paper proposes a novel version vector called log ′ (log-prime) consisting of only three entries. By encoding based on the characteristics of prime numbers, log ′ version vectors of fixed size can be logged concisely with no pruning technique at a little sacrifice in accuracy. Simulation studies show that log ′ version vectors are accurate enough to detect almost all conflicts in the replication systems where all replicas are fully synchronizing.

Concise version vectors in WinFS

Conflicts naturally arise in optimistically replicated systems. The common way to detect update conflicts is via version vectors, whose storage and communication overhead are number of replicas × number of objects. These costs may be prohibitive for large systems. This paper presents predecessor vectors with exceptions (PVEs), a novel optimistic replication technique developed for Microsoft’s WinFS system. The paper contains a systematic study of PVE’s performance gains over traditional schemes. The results demonstrate a dramatic reduction of storage and communication overhead in normal scenarios, during which communication disruptions are infrequent. Moreover, they identify a cross-over threshold in communication failure-rate, beyond which PVEs loses efficiency compared with traditional schemes.

Comments on "Detection of Mutual Inconsistency in Distributed Systems"

In the above paper,1authors have given a technique for the detection of mutual inconsistency among the copies of a file, in presence of network partitioning. This technique involves maintaining a vector with each file in a partition. Here, we show that it is impossible to maintain the version vectors when arbitrary reconfigurations can occur after a network partitioning.

Detection of Mutual Inconsistency in Distributed Systems

Many distributed systems are now being developed to provide users with convenient access to data via some kind of communications network. In many cases it is desirable to keep the system functioning even when it is partitioned by network failures. A serious problem in this context is how one can support redundant copies of resources such as files (for the sake of reliability) while simultaneously monitoring their mutual consistency (the equality of multiple copies). This is difficult since network faiures can lead to inconsistency, and disrupt attempts at maintaining consistency. In fact, even the detection of inconsistent copies is a nontrivial problem. Naive methods either 1) compare the multiple copies entirely or 2) perform simple tests which will diagnose some consistent copies as inconsistent. Here a new approach, involving version vectors and origin points, is presented and shown to detect single file, multiple copy mutual inconsistency effectively. The approach has been used in the design of LOCUS, a local network operating system at UCLA.