1. A stream data processing method for processing, on a computer comprising a processor and a memory, input tuples that are received from a plurality of data sources, the stream data processing method comprising: a first step of setting, by the computer, a processing holdback period by the computer; a second step of receiving, by the computer, the input tuples comprising data time stamps that are attached by the plurality of data sources and identifiers of the plurality of data sources; a third step of generating, by the computer, a holdback tuple by attaching to each of the received input tuples a system time stamp that indicates a time of reception of the each of the received input tuples; a fourth step of storing, by the computer, the holdback tuple in a data source-based queue that is associated with the identifier of the data source of the holdback tuple; a fifth step of reading, by the computer, data time stamps of hold back tuples at heads of the data source-based queues, and sorting the data source-based queues in an order of the data time stamps of the head holdback tuples; a sixth step of identifying, by the computer, a data source-based queue that stores at a head a holdback tuple that has a smallest data time stamp value, reading a system time stamp of the head holdback tuple, and determining whether or not a current system time stamp value is larger than a value that is obtained by adding the processing holdback period to the read system time stamp; a seventh step of obtaining, by the computer, when it is determined that the current system time stamp value is larger, an input tuple from the head holdback tuple of the identified data source-based queue, and putting the obtained input tuple into an input stream thereby maintaining an order of time stamps of the input tuples; and an eighth step of executing, by the computer, a given query for the input tuple put into the input stream.