A data processing program comprising instructions which, when the program is executed by a computer that is one of a plurality of computers (300, 400, 500, 600) included in a data processing system that comprises a first processing system and a second processing system, cause the computer to execute processing, the processing comprising: each time the data processing system receives a piece of data included in stream data transmitted from a plurality of internet of things, IoT, devices (31, 32,...), obtaining the received piece of data from the data processing system, the stream data including a plurality of pieces of data, each of the plurality of pieces of data being data that has been transmitted from any one of the plurality of IoT devices and that includes time information, the time information comprising a timestamp; comparing the time information of the data with a switching time set as a time to switch between the first processing system and the second processing system; when the computer operates as the first processing system, outputting a processing result of processing that uses the data in a case where time indicated by the time information of the data is before the switching time, and refraining from the outputting of the processing result in a case where time indicated by the time information of the data is equal to or after the switching time; and when the computer operates as the second processing system, refraining from the outputting of the processing result in a case where time indicated by the time information of the data is before the switching time, and outputting the processing result of processing that uses the data in a case where the time indicated by the time information of the data is equal to or after the switching time. each time the data processing system receives a piece of data included in stream data transmitted from a plurality of internet of things, IoT, devices (31, 32,...), obtaining the received piece of data from the data processing system, the stream data including a plurality of pieces of data, each of the plurality of pieces of data being data that has been transmitted from any one of the plurality of IoT devices and that includes time information, the time information comprising a timestamp; comparing the time information of the data with a switching time set as a time to switch between the first processing system and the second processing system; when the computer operates as the first processing system, outputting a processing result of processing that uses the data in a case where time indicated by the time information of the data is before the switching time, and refraining from the outputting of the processing result in a case where time indicated by the time information of the data is equal to or after the switching time; and when the computer operates as the second processing system, refraining from the outputting of the processing result in a case where time indicated by the time information of the data is before the switching time, and outputting the processing result of processing that uses the data in a case where the time indicated by the time information of the data is equal to or after the switching time.