A master disc has a pattern of soft magnetic film in which the length thereof or the interval between soft magnetic material and another soft magnetic material is kept less than a predetermined value. The reflective pet leash reflects incoming light beams back in the same direction as emanated. At least one fragment of the query execution is distributed to at least one worker node in the shared disk database cluster, and the object identification data is utilized for multiversion concurrency control during query execution by the leader node and at least one worker node. A relative proportion of watermark levels of I-picture, B-picture, and P-picture is preferably set to 10:7:5.