Optimal maintenance policy for a database system with additive garbages

It recently needs to maintain a database periodically and economically for the requirement of continuous operation of a computer system. To use storage areas effectively and to improve a processing efficiency, garbage collections of a database are made at suitable times according to the number and amount of updating procedures. However, it would be impossible to take much time for any maintenances of a database, since it is not good to reduce services of users and to stop processings for online sysems. Effectual and economical maintenance plans must be made at the beginning of operations. This paper considers that additive garbages arise when a database is updated, and they reduce storage areas and make worse a processing efficiency. To prevent such matters, a database is checked at a constant time T. It total garbages exceed a threshold level k, a garbage collection is made. An expected cost of this model is obtained and an optimal value k* to minimize it is discussed. A numerical example is finally given. [In Japanese.]