A method of increasing a processing performance by setting a suitable upper limit of a resources count for each processing request according to an arrangement of hardware such as a storage device or to contents of the processing request. A processing request acceptor accepts the processing request as a data query. An auxiliary storage device forms a storage area where a database is stored. A data operation executor analyzes the accepted processing request and executed the data operations on the basis of the analyzed result. A resource manager manages the respective data operations allocated to generated processes or threads. A buffer manager caches data of the data operations upon execution of the data operations from the auxiliary storage device to a memory, and determines whether or not the data as the target of the data operations are present in the cache.