A COMPARISON OF FILE ALLOCATION DECISION-MAKING SCHEMES (REPLICATED FILES, DISTRIBUTED NETWORKS, SIMULATION EXPERIMENTS, DISTRIBUTED DATABASES)

摘要

We compare decentralized file allocation decision-making to centralized file allocation decision-making. The file allocation problem is the assignment of copies of a file to nodes on a distributed network to optimize some network performance measure. In decentralized file allocation decision-making each node independently decides the placement of some copies of a file. While in centralized file allocation decision-making, one central node decides where all copies are placed. Decentralized file allocation decision-making is resilient to a number of node failures, uses minimum computational resources, takes advantage of concurrent processing and is adaptable to distributed networks. On the other hand, we expect decentralized file allocation decision-making to produce solutions which are no better than those produced by centralized file allocation decision-making. The tradeoff is between optimality of the solution and the amount of resources used to obtain the solution.;The method used for comparison is experimental. The principal measure of performance used in the comparison is mean data access time. The performance of the file allocation decision-making schemes being examined is compared for various network topologies and varying workloads.;We find that we can describe a simple robust scheme for decentralized file allocation decision-making which is efficient and resulting file assignments perform decently in a distributed network. Additionally, we discover a relationship between the performance of file allocation decision-making schemes and network topologies.;Contributions of this thesis include: (a) A characterization of time-variant workload to aid in the study of the effects of time-variant workload. (b) A model for the integration of the file allocation function and a DDBMS. (c) A specific decentralized file allocation algorithm for computation of file assignments. (d) A scheme for decentralized control of copies of a file using tokens. (e) A simulator to perform the comparison tests of this thesis and in future research.