1. A method for a operating data center, wherein the data center includes a job tracker, map task trackers and reduce task trackers, the method comprising: in response to a map task distributed by the job tracker, executing, via a map task tracker, the map task to generate a map output including version information; storing, via the map task tracker, the generated map output; informing, via the map task tracker, the job tracker of related information of the map output; in response to a reduce task distributed by the job tracker, acquiring, via the reduce task tracker, map outputs for key names including given version information from the map task trackers, wherein the acquired map outputs include the map outputs including the given version information and historical map outputs including the version information prior to the given version information; and executing, via the reduce task tracker, the reduce task on the acquired map outputs.