Optimization of the Number of Copies in a Distributed Data Base

We consider the effect on system performance of the distribution of a data base in the form of multiple copies at distinct sites. The purpose of our analysis is to determine the gain in READ throughput that can be obtained in the presence of consistency preserving algorithms that have to be implemented when UPDATE operations are carried out on each copy. We show that READ throughput diminishes if the number of copies exceeds an optimal value. The theoretical model we develop is applied to a system in which consistency is preserved through the use of Ellis´ ring algorithm.