Abstract: A data synchronization method is provided to enhance reliability and performance of the database. The data reflection method selection unit of the active server weights collected values in the resource utilization table by multiplying the collected values by assessment coefficients assigned to the individual collected values in an assessment coefficient table and sums up the weighted values to calculate an assessment value for each data reflection method, and determines the data reflection method whose assessment value is minimum. The log data transmission unit, according to the determined data reflection method, sends log data that is reflected on the active database to the standby server, which forms one of the duplicated servers making up the redundant configuration. The data reflection method identifies the content to be transmitted.