Database management system and database management method

A database management method comprising:

• performing an import process that is a process for importing, into a table in a database, a chunk in a store format indicated by a base type that is information indicating a store format of the table,
• the import process not being executable during a data conversion process, the data conversion process being a process for converting a non-converted chunk that is a chunk in a store format different from the store format indicated by the base type, among all chunks in the table, into a chunk in the store format indicated by the base type, each chunk being an import unit of data into the table;
• performing, in response to a conversion request that is a request to convert the store format of the table, a base type change process for changing the store format indicated by the base type that is information indicating the store format of the table into a store format according to the conversion request;
• performing the data conversion process asynchronously with the base type change process that is performed in response to the conversion request;
• and
• importing into the table, in the import process after execution of the base type change process, a chunk in a store format indicated by the base type after change.