A database-management system easy for system integration and flexible to functional modifications, etc., is provided. A database stored in each main-memory area of a plurality of computers connected via network is managed as follows: a first computer storing original data of at least a piece of data of the database is designated as a base host. At least one second computer storing replica data of the original data is designated as a replica host. A retrieving procedure is performed to receive data to be stored in a third computer from the base host storing the original data or the replica host storing the replica data in startup of the third computer, and store the received data in the main-memory of the third computer.