1. A data processing control method comprising: first assigning, by a processor device of a server, when assigning input data to normal Reduce tasks and a spare Reduce task that are performed by using results of Map processes in a MapReduce process, input data with a smaller amount than any of amounts of the input data which is assigned to the normal Reduce tasks to the spare Reduce task; and second assigning, by the processor device of the server, the normal Reduce tasks and the spare Reduce task, to which the input data is assigned, to a server that performs Reduce processes in the MapReduce process such that the spare Reduce task is started after the assignment of all of the normal Reduce tasks.