A Powerful Optimization Approach for the Multi Channel Dissemination Networks

In the wireless environment, dissemination techniques may improve data access for the users. In this paper, we show a description of dissemination architecture that fits the overall telecommunication network. This architecture is designed to provide efficient data access and power saving for the mobile units. A concurrency control approach, MCD, is suggested for data consistency and conflict checking. A performance study shows that the power consumption, space overhead, and response time associated with MCD is far less than other previous techniques.Comment: 9 Pages, IJCNC Journal 201

Transactional concurrency control for resource constrained applications

PhD ThesisTransactions have long been used as a mechanism for ensuring the consistency of databases. Databases, and associated transactional approaches, have always been an active area of research as different application domains and computing architectures have placed ever more elaborate requirements on shared data access. As transactions typically provide consistency at the expense of timeliness (abort/retry) and resource (duplicate shared data and locking), there has been substantial efforts to limit these two aspects of transactions while still satisfying application requirements. In environments where clients are geographically distant from a database the consistency/performance trade-off becomes acute as any retrieval of data over a network is not only expensive, but relatively slow compared to co-located client/database systems. Furthermore, for battery powered clients the increased overhead of transactions can also be viewed as a significant power overhead. However, for all their drawbacks transactions do provide the data consistency that is a requirement for many application types. In this Thesis we explore the solution space related to timely transactional systems for remote clients and centralised databases with a focus on providing a solution, that, when compared to other's work in this domain: (a) maintains consistency; (b) lowers latency; (c) improves throughput. To achieve this we revisit a technique first developed to decrease disk access times via local caching of state (for aborted transactions) to tackle the problems prevalent in real-time databases. We demonstrate that such a technique (rerun) allows a significant change in the typical structure of a transaction (one never before considered, even in rerun systems). Such a change itself brings significant performance success not only in the traditional rerun local database solution space, but also in the distributed solution space. A byproduct of our improvements also, one can argue, brings about a "greener" solution as less time coupled with improved throughput affords improved battery life for mobile devices

Uma proposta diferenciada de taxonomia para mecanismos de controle de concorrência de bancos de dados em ambientes sem fio

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico. Programa de Pós-Graduação em Ciência da Computação.O objetivo fundamental do controle de concorrência em banco de dados é assegurar que a execução concorrente de transações não resulte na perda da consistência do banco de dados, ou seja, é necessário assegurar o isolamento das transações. No que diz respeito aos bancos de dados móveis, os mecanismos de controle de concorrência aplicados em bancos de dados tradicionais, ou até mesmo distribuídos, não satisfazem as restrições impostas pelo ambiente de computação móvel, como mobilidade das unidades, as freqüentes desconexões de rede, a baixa largura de banda e a portabilidade. Baseando-se na referida fundamentação, neste trabalho é feito um estudo bibliográfico dos principais modelos de transações móveis, evidenciando suas arquiteturas, modos de processamento, tipos de transações utilizadas, traçando um comparativo de como é feito o suporte das propriedades ACID (Atomicidade, Consistência, Isolamento e Durabilidade) em cada modelo estudado. Com estas informações é feita uma análise dos mecanismos de controle de concorrência utilizados em cada modelo. De acordo com as necessidades dos modelos de transações investigados na literatura, a taxonomia proposta tem como diferencial a apresentação da abordagem híbrida, onde os modelos de transações móveis poderão obter um melhor desempenho utilizando o modo pessimista, quando a conectado ao banco de dados, e otimista quando desconectado

Efficient Concurrency Control for Broadcast Environments

A crucial consideration in environments where data is broadcast to clients is the low bandwidth available for clients to communicate with servers. Advanced applications in such environments do need to read data that is mutually consistent as well as current. However, given the asymmetric communication capabilities and the needs of clients in mobile environments, traditional serializability-based approaches are too restrictive, unnecessary, and impractical. We thus propose the use of a weaker correctness criterion called update consistency and outline mechanisms based on this criterion that ensure (1) the mutual consistency of data maintained by the server and read by clients, and (2) the currency of data read by clients. Using these mechanisms, clients can obtain data that is current and mutually consistent "off the air", i.e., without contacting the server to, say, obtain locks. Experimental results show a substantial reduction in response times as compared to existing (serializabilit..

Abstract Efficient Concurrency Control for Broadcast Environments

A crucial consideration in environments where data is broad-cast to clients is the low bandwidth available for clients to communicate with servers. Advanced applications in such environments do need to read data that is mutually consis-tent as well as current. However, given the asymmetric com-munication capabilities and the needs of clients in mobile en-vironments, traditional serializability-based approaches are too restrictive, unnecessary, and impractical. We thus pro-pose the use of a weaker correctness criterion called update consistency and outline mechanisms based on this criterion that ensure (1) the mutual consistency of data maintained by the server and read by clients, and (2) the currency of data read by clients. Using these mechanisms, clients can obtain data that is current and mutually consistent “off the air”, i.e., without contacting the server to, say, obtain locks. Experimental results show a substantial reduction in re-sponse times as compared to existing (serializability-based) approaches. A further attractive feature of the approach is that if caching is possible at a client, weaker forms of currency can be obtained while still satisfying the mutual consistency of data.