Provided a plurality of data nodes connected in a network, each including a data storage unit. The data node of data replication destination temporarily stores data to be updated in an intermediate data structure, and converts asynchronously with respect to the update request to a target data structure to store the converted data in the data storage unit. Based on access history information stored in an access history recording unit, trigger information, concerning timing for execution of conversion to the target data structure performed asynchronously by the data node is changed.