Prinzipien der Replikationskontrolle in verteilten Datenbanksystemen?

Durch Datenreplikation können prinzipiell schnellere Zugriffszeiten und eine beliebig hohe Fehlertoleranz in verteilten Datenbanksystemen erreicht werden. Anderseits erhöht Replikation die Gefahr von Inkonsistenzen und den Aufwand von Änderungsoperationen. Zur Lösung dieses Zielkonflikts wurden in der Literatur viele unterschiedliche Replikationsverfahren vorgeschlagen. Dieser Überblicksartikel beschreibt die den einzelnen Verfahren zugrundeliegenden Prinzipien zur Replikationskontrolle. Dazu werden die durch den Kopieneinsatz resultierenden Probleme erläutert, daraus Kriterien zur anschließenden Klassifikation abgeleitet und danach ausgewählte Replikationsverfahren näher vorgestellt

A high availability cluster-based replica control protocol in data grid

Data replication is widely used to provide high data availability, and increase the performance of the distributed systems. Many replica control protocols have been proposed in distributed and grid environments that achieved both high performance and availability.However, the previously proposed protocols still require a bigger number of replicas for read and write operations which are not suitable for a large scale system such as data grid.In this paper, a new replica control protocol called Clustering based Hybrid (CBH) has been proposed for managing the data in grid environments. We analyzed the communication cost and data availability for the operations and compared CBH protocol with recently proposed replica control protocols called Dynamic Hybrid (DH) protocol and Diagonal Replication in 2D Mesh (DR2M) protocol.To evaluate CBH protocol, a simulation model was implemented using Java. Our results show that for the read operations, CBH protocol improves the performance of communication cost and data availability compared to the DH and DR2M protocols

Swarm Based Implementation of a Virtual Distributed Database System in a Sensor Network

The deployment of unmanned aerial vehicles (UAVs) in recent military operations has had success in carrying out surveillance and combat missions in sensitive areas. An area of intense research on UAVs has been on controlling a group of small-sized UAVs to carry out reconnaissance missions normally undertaken by large UAVs such as Predator or Global Hawk. A control strategy for coordinating the UAV movements of such a group of UAVs adopts the bio-inspired swarm model to produce autonomous group behavior. This research proposes establishing a distributed database system on a group of swarming UAVs, providing for data storage during a reconnaissance mission. A distributed database system model is simulated treating each UAV as a distributed database site connected by a wireless network. In this model, each UAV carries a sensor and communicates to a command center when queried. Drawing equivalence to a sensor network, the network of UAVs poses as a dynamic ad-hoc sensor network. The distributed database system based on a swarm of UAVs is tested against a set of reconnaissance test suites with respect to evaluating system performance. The design of experiments focuses on the effects of varying the query input and types of swarming UAVs on overall system performance. The results show that the topology of the UAVs has a distinct impact on the output of the sensor database. The experiments measuring system delays also confirm the expectation that in a distributed system, inter-node communication costs outweigh processing costs