Sizes of buffer pools for temporarily storing data from a database are dynamically optimized. A database server includes: a dividing ratio setting unit for setting a dividing ratio for dividing a memory area of a predetermined size into a plurality of buffer pools used selectively according to a type of transaction or type of data; a response time measuring unit for measuring response time of transactions; a response time computation formula generating unit for calculating parameters of a response time calculation formula for calculating the response time based on the size of each of the plurality of buffer pools from the set dividing ratio and the measured response time; and a dividing ratio calculation unit for calculating the dividing ratio that minimizes the response time by using the response time calculation formula; wherein the dividing ratio setting unit sets the dividing ratio calculated by the dividing ratio calculating unit.