An Efficient Concurrency Control Technique for Mobile Database Environment

Day by day wireless networking technology and mobile computing devices are becoming more popular for their mobility as well as great functionality Now it is an extremely growing demand to process mobile transactions in mobile databases that allow mobile users to access and operate data anytime and anywhere irrespective of their physical positions Information is shared among multiple clients and can be modified by each client independently However for the assurance of timely access and correct results in concurrent mobile transactions concurrency control techniques CCT happen to be very difficult Due to the properties of Mobile databases e g inadequate bandwidth small processing capability unreliable communication mobility etc existing mobile database CCTs cannot employ effectively With the client-server model applying common classic pessimistic techniques of concurrency control like 2PL in mobile database leads to long duration Blocking and increasing waiting time of transactions Because of high rate of aborting transactions optimistic techniques aren t appropriate in mobile database as well This paper discusses the issues that need to be addressed when designing a CCT technique for Mobile databases analyses the existing scheme of CCT and justify their performance limitations A modified optimistic concurrency control scheme is proposed which is based on the number of data items cached amount of execution time and current load of the database server Experimental results show performance benefits such as increase in average response time and decrease in waiting time of the transaction

Maintaining consistency in client-server database systems with client-side caching

PhD ThesisCaching has been used in client-server database systems to improve the performance of applications. Much of the current work has concentrated on caching techniques at the server side, since the underlying assumption has been that clients are “thin” with application level processing taking place mainly at the server side. There are also a new class of “thick client” applications where clients need to access the database at the server but also perform substantial amount of processing at the client side; here client-side caching is needed to provide good performance for applications. This thesis presents a transactional cache consistency scheme suitable for systems with client-side caching. The scheme is based on the optimistic approach to concurrency control. The scheme provides serializability for committed transactions. This is in contrast to many modern systems that only provide the snapshot isolation property which is weaker than serializability. A novel feature is that the processing load for validating transactions at commit time is shared between clients and the database server, thereby reducing the load at the server. Read-only transactions can be validated at the client-side, without communicating with the server. Another feature is that the scheme permits disconnected operation, allowing clients with cached objects to work offline. The performance of the scheme is evaluated using simulation experiments. The experiments demonstrate that for mostly read only transaction load – for which caching is most effective - the scheme outperforms the existing concurrency control scheme with client-side caching considered to be the best, and matches the performance of the widely used scheme that only provides snapshot isolation. The results also show that the scheme in a disconnected environment provides reasonable performance.Directorate General of Higher Education, Ministry of National Education, Indonesia

The Economic Impacts of Information and Communication Technology In The Hungarian Economy

As the author could not find a reassuring mathematical and statistical method in the literature for studying the effect of information communication technology on enterprises, the author suggested a new research and analysis method that he also used to study the Hungarian economic sectors. After a brief introduction to the theoretical background of the Information Age, the author examines the question of what factors have an effect on their net income is essential for enterprises. First, the potential indicators related to economic sectors were studied, then the author compared those indicators to the net income of the surveyed enterprises. The data resulting from the comparison showed that the growing penetration of electronic marketplaces contributed to the change of the net income of enterprises in various economic sectors to the extent of 37 %. Among all the potential indicators, only the indicator of electronic marketplaces has a direct influence on the net income of enterprises. It was practical to determine two clusters based on the potential indicators

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