Browsing by Subject "performance evaluation"

Now showing 1 - 3 of 3

Open Access
Counteracting free riding in pure peer-to-peer networks
(2008) Karakaya, K. Murat
The peer-to-peer (P2P) network paradigm has attracted a significant amount of interest as a popular and successful alternative to traditional client-server model for resource sharing and content distribution. However, researchers have observed the existence of high degrees of free riding in P2P networks which poses a serious threat to effectiveness and efficient operation of these networks, and hence to their future. Therefore, eliminating or reducing the impact of free riding on P2P networks has become an important issue to investigate and a considerable amount of research has been conducted on it. In this thesis, we propose two novel solutions to reduce the adverse effects of free riding on P2P networks and to motivate peers to contribute to P2P networks. These solutions are also intended to lead to performance gains for contributing peers and to penalize free riders. As the first solution, we propose a distributed and localized scheme, called Detect and Punish Method (DPM), which depends on detection and punishment of free riders. Our second solution to the free riding problem is a connection-time protocol, called P2P Connection Management Protocol (PCMP), which is based on controlling and managing link establishments among peers according to their contributions. To evaluate the proposed solutions and compare them with other alternatives, we developed a new P2P network simulator and conducted extensive simulation experiments. Our simulation results show that employing our solutions in a P2P network considerably reduces the adverse effects of free riding and improves the overall performance of the network. Furthermore, we observed that P2P networks utilizing the proposed solutions become more robust and scalable.
Open Access
An implementation of a temporal relational database management system
(1992) Goralwalla, Iqbal A.
111 this work, the implementation of a temporal database management system is reported. This system has been implemented on top of an existing database system that manipulates relations with set-valued attributes. The temporal relational model together with the tem])oral algebra are descril)ed. The basic set of opercitions of the extended relational algebra have been modified to handle temporal attributes. New operations have been added to help in the extraction of information from historical relations. These operations convcirt one attrilnite type to another and do selection over the time'dimension. Moreover, a statistical interface has been added to the system. This interface includes aggregate functions and a new operation, enumeration^ which derives a table of uniform data for a set of time points or intervals, from a three dimensional historical relation. A performance evaluation of the system is carried out by executing sample queries against different types of databases: snapshot, snapshot/nested and historical.
Open Access
Transaction execution in multidatabase systems
(1996) Devirmiş, Timuçin
Most work in the multiclatabase systems (MDBSs) area has focused on the issues of transaction management and concurrency control. It is difficult to implement traditional transaction management techniques in a MDBS due to the heterogeneity and autonomy of the connected local sites. In this thesis, we present a new transaction execution model that captures the formalism and semantics of various extended transaction models and adopts them to a MDBS environment. The proposed model covers nested transactions, various dejjendenc}' types among subtransactions, and commit-independent transactions. The execution model does not make any assumption regarding the concurrency control protocols executed at the local sites connected to the MDBS. VVe also present a detailed simulation model of a MDBS to aiiiilyze the performance of the proposed model. The performances of both the traditional transaction model and the proposed transaction model are evaluated under a range of workloads and system configurations. The performance impact of global transactions’ behavior on local transactions is also discussed.