According to an embodiment, a database system includes nodes and a management device. The management device includes first and second assigning units. Depending on change in state of each node, the first assigning unit assigns a first node storing data pieces and receiving an access request to the data pieces, and assigns a second node serving as a backup node, and instructs each node to perform operations according to assignment. Depending on state of nodes and change in assignment state, the second assigning unit assigns a third node as a candidate node serving as the first node, and instructs each node to make preparation for causing the third node to operate as the first node. Each node sends, to the third node, a snapshot of the data pieces at the first time point and an operation log according to the access request at and after the first time point.