Database system, computer program product, and data processing method

A management device that manages a plurality of nodes which stores therein a database, the management device comprising:

• a first assigning unit configured to, depending on a change in state of each of the plurality of nodes, assign a first node, which stores therein data pieces and receives an access request with respect to the data pieces, and assign a second node, which stores therein the data pieces and serves as a backup node for the first node, and to instruct each of the plurality of nodes to perform operations according to assignment;
• and
• a second assigning unit configured to, depending on a state of the plurality of nodes and depending on a change in assignment state of the first node and the second node, assign a third node which is a candidate node to serve as the first node or the second node, and to instruct each of the plurality of nodes to make preparation for causing the third node to operate as the first node or the second node, wherein
• each of the plurality of nodes sends the data pieces of the first node or the second node to the third node.

A data processing method implemented in a database system that includes a plurality of nodes in which a database is stored and includes a management device which manages the plurality of nodes, wherein

• the management device executes
• a first assigning step that, depending on a change in state of each of the plurality of nodes, includes assigning a first node, which stores therein data pieces and receives an access request with respect to the data pieces, and assigning a second node, which stores therein the data pieces and which serves as a backup node for the first node, and includes instructing each of the plurality of nodes to perform operations according to assignment;
• and
• a second assigning step that, depending on a state of the plurality of nodes and depending on a change in assignment state of the first node and the second node, includes assigning a third node which is a candidate node to serve as the first node or the second node, and includes instructing each of the plurality of nodes to make preparation for causing the third node to operate as the first node or the second node, and
• each of the plurality of nodes executes a transferring step that includes sending the data pieces of the first node or the second node to the third node.