An information processing system, a data update method and a data update program are disclosed. In a data base system of master-slave configuration, the update result can be accessed also on slave side with the access request immediately after the particular update. The data base system DBS includes a master DB computer and at least a slave DB computer. The slave DB computer judges from the count on an update counter table whether the update log received from the master DB computer is to be reflected in a duplicate data base or not. Thus, the lost update problem is solved while at the same time realizing a high-speed process.