Database management system and computer system

Provided is a database management system comprising the following: a first query execution unit that executes a query on the basis of a query execution plan for querying a database, and returns the query execution results to the query publisher; and a buffer management unit configured so that when a data read request has been received, if the read-request data is not stored in a buffer, the read-request data is read from the database, is stored in the buffer, and is provided to the read-request publisher, and if the read-request data is already stored in the buffer, the read request data is read from the buffer and provided to the read-request publisher. A second query execution unit is added to the database management system. The second query execution unit executes a query on the basis of the query execution plan, and in the query execution procedure, issues a necessary-data read request to the buffer management unit. Due to the foregoing, when the first query execution unit issues a data read request, it is possible for such data to be already stored in the buffer.