A multi-master node model database management technology involves notifying a higher-level master node of a transaction minimum value as a minimum value of an implementation-underway transaction in a snapshot from a lower-level master node, comparing the transaction minimum value with minimum values retained by the respective master nodes and thus updating a node minimum value and a cluster minimum value. Then, the lower-level master node transmits a write set containing a shadow copy of its own database, a heap tuple map deployed on its own memory and the transaction minimum value to the higher-level master node, and the higher-level master node receiving the write set updates the database by use of the write set if the transaction minimum value is equal to or larger than the cluster minimum value, and aborts the write set if the transaction minimum value is smaller than the cluster minimum value.