One embodiment of the present invention provides a system that facilitates merging different versions of a database object. A first detection coil and a second detection coil are arranged to face the first magnetostrictive film, and a third detection coil and a fourth detection coil are arranged to face the second magnetostrictive film. Flow characteristics of the virtualized cluster system are detected at a regular time cycle, a power-efficiency management policy is generated for each of at least one back-end physical host based on the detected flow characteristics, and the power-efficiency management policies are performed.