File Allocation and Join Site Selection Problem in Distributed Database Systems.

There are two important problems associated with the design of distributed database systems. One is the file allocation problem, and the other is the query optimization problem. In this research a methodology that considers both these aspects is developed that determines the optimal location of files and join sites for given queries simultaneously. Using this methodology, three different mixed integer programming models that describe three cases of the file allocation and join site selection problem are developed. Dual-based procedures are developed for each of the three mixed integer programming models. Extensive computational testing is performed which shows that the dual-based algorithms developed are able to generate solutions which are very close to the optimal. Also, these near optimal solutions are found very quickly, even for large scale problems

Multiprocessor scheduling with practical constraints

The problem of scheduling tasks onto multiprocessor systems has increasing practical importance as more applications are being addressed with multiprocessor systems. Actual applications and multiprocessor systems have many characteristics which become constraints to the general scheduling problem of minimizing the schedule length. These practical constraints include precedence relations and communication delays between tasks, yet few researchers have considered both these constraints when developing schedulers. This work examines a more general multiprocessor scheduling problem, which includes these practical scheduling constraints, and develops a new scheduling heuristic using a list scheduler with dynamically computed priorities. The dynamic priority heuristic is compared against an optimal scheduler and against other researchers’ approaches for thousands of randomly generated scheduling problems. The dynamic priority heuristic produces schedules with lengths which are 10% to 20% over optimal on the average. The dynamic priority heuristic performs better than other researchers’ approaches for scheduling problems with the practical constraints. We conclude that it is important to consider practical constraints in the design of a scheduler and that a simple heuristic can still achieve good performance in this area

Methodology for modeling high performance distributed and parallel systems

Performance modeling of distributed and parallel systems is of considerable importance to the high performance computing community. To achieve high performance, proper task or process assignment and data or file allocation among processing sites is essential. This dissertation describes an elegant approach to model distributed and parallel systems, which combines the optimal static solutions for data allocation with dynamic policies for task assignment. A performance-efficient system model is developed using analytical tools and techniques. The system model is accomplished in three steps. First, the basic client-server model which allows only data transfer is evaluated. A prediction and evaluation method is developed to examine the system behavior and estimate performance measures. The method is based on known product form queueing networks. The next step extends the model so that each site of the system behaves as both client and server. A data-allocation strategy is designed at this stage which optimally assigns the data to the processing sites. The strategy is based on flow deviation technique in queueing models. The third stage considers process-migration policies. A novel on-line adaptive load-balancing algorithm is proposed which dynamically migrates processes and transfers data among different sites to minimize the job execution cost. The gradient-descent rule is used to optimize the cost function, which expresses the cost of process execution at different processing sites. The accuracy of the prediction method and the effectiveness of the analytical techniques is established by the simulations. The modeling procedure described here is general and applicable to any message-passing distributed and parallel system. The proposed techniques and tools can be easily utilized in other related areas such as networking and operating systems. This work contributes significantly towards the design of distributed and parallel systems where performance is critical

Design issues in distributed management information systems.

Thesis. 1978. Ph.D.--Massachusetts Institute of Technology. Alfred P. Sloan School of Management.MICROFICHE COPY AVAILABLE IN ARCHIVES AND DEWEY.Includes bibliographical references.Ph.D