A data processing system includes a data processing unit which processes data acquired and a plurality of data retaining units which store databases used to process the data. Each of the plurality of data retaining units stores a primary database in common and stores the respective shares of a secondary database. The primary database stores a list of IDs for identifying data to be processed by any one of the plurality of data processing units. Each of the data processing units is notified of a range of IDs that the data processing unit handles, among the list of IDs stored in the primary database, and, when acquiring a packet containing an ID that lies within the range of IDs, the data processing unit processes the packet.