Optimal Policies for Data Base Reorganization

One of the problems faced by a Data Base Administrator is the determination of a file reorganization policy. The Data Base Administrator has to balance the benefits of a reorganization, which restores processing efficiency and hence reduces operating costs, against the extra expenditures involved (unloading and reloading the files, system unavailability costs, etc.). In this paper we consider both policies of state-dependent reorganization and reorganization at fixed time intervals. We prove that the optimal state-dependent policy belongs to the class of control-limit rules, and show how the optimal control-limit can be evaluated. We then consider the policy of reorganization at fixed time intervals, and show that, when the record arrival process is Poisson, this policy is always inferior to the optimal control-limit rule (for the average-cost criterion). We conclude with an example where operating and reorganization costs increase linearly with system occupancy.