Abstract:
A method and device for guaranteeing performance of stream data processing wherein a latency guarantee and a processing accuracy guarantee are possible while ensuring a real-time property. An execution system determination unit evaluates an amount of data currently present in a queue of an input data reception unit, calculation time, and the processing accuracy. Then, during a query process, if the amount of data in the queue increases for some reason, and is likely to be larger than the requested latency, the execution system determination unit changes the system to a calculation system by which the latency can be reduced within a range that a final quality can be allowed, on the basis of the evaluation result. Under the condition that the accuracy is reduced, if the latency is likely to be greatly lower than the requested latency, the system changes to a calculation system having a higher processing accuracy.

Description:
TECHNICAL FIELD   
       [0001]    The present invention relates to a stream data processing system and more specifically to a technology of guaranteeing performance such as latency and processing accuracy in stream data processing. 
       BACKGROUND ART  
       [0002]    Normal stream data processing continuously performs processing, judgment, interpolation, estimation, etc. on continuous data (see Patent Literature 1). However, upon sudden data increase, latency is reduced, and real-time property desired by the user can no longer be maintained. 
         [0003]    On the other hand, in a numerical value calculation field, there is a method of previously preparing a plurality of calculation systems, and by using past calculation results of each calculation system, in a manner such as to satisfy latency and processing accuracy requested by the user, making automatic selection on which calculation system is to be used (see Patent Document 2). 
       CITATION LIST  
     Patent Literature 
       [0000]    
       
         Patent Literature 1: US Patent Application Laid-open US 2008/0005392 
         Patent Literature 2: Japanese Patent Application Laid-open No. 2007-34375 
       
     
       SUMMARY OF INVENTION  
     Technical Problem 
       [0006]    In the stream data processing, upon sudden data increase as described above, different actions (whether or not to maintain the latency even while accuracy is reduced and conversely, whether or not to maintain the accuracy even while sacrificing the latency to some extent) need to be taken depending on applications. For example, even while sacrificing the accuracy to some extent for estimation of power consumption of the next time in each household, image real-time compression processing, prediction of information device failure indication, etc., the latency needs to be maintained. Conversely, the accuracy cannot be reduced for a security field, economic index calculation, etc. There are demands for a mechanism that permits inputting of such an application request and supporting it. 
         [0007]    In Patent Literature 1, a capability of applying to a query an external definition function created by a vendor is installed in a server, and in order to guarantee latency therein, sorting to a different server is performed or part of input tuple is eliminated from a resource used amount of the server, which raises a problem that a plurality of servers are required or that there arises a risk that acquired results differ as a result of eliminating part of the input data. 
         [0008]    Thus, in a case where it is considered to apply the method of the numerical calculation field in Patent Literature 2 to the external definition function in the stream data processing in Patent Literature 1, means for estimating latency beforehand is not sufficient, thus raising a problem of delayed calculation system switching. Moreover, there is no mechanism of controlling the whole, and thus there arises a problem that each function selects a calculation system without considering latency and processing accuracy of the entire processing. 
         [0009]    It is an object of the invention to solve the problems described above and provide a method and a device for guaranteeing performance in stream data processing capable of guaranteeing latency and further guaranteeing processing accuracy while ensuring real-time property. 
       Solution to Problem 
       [0010]    To address the object described above, provided in the present invention is a performance guarantee method in stream data processing executed by a computer provided with a processing unit and an interface unit. The performance guarantee method includes a plurality of execution systems with different processing performances for the stream data processing. The processing unit estimates, upon execution of the stream data processing on input data received via the interface unit, a performance value based on an amount of the unprocessed input data, determines, based on the estimated performance value, the execution system that satisfies a requested performance value, makes switching to the determined execution system and executes the stream data processing, and outputs processing results as output data to the interface unit. 
         [0011]    Moreover, to address the object of the invention, there is provided, in the invention, a performance guarantee device in stream data processing includes: an input data reception unit receiving input data; a processing unit executing query processing on the input data; a data transmission unit outputting execution results as output data; and a request input unit receiving a requested performance value, wherein the processing unit includes a plurality of execution systems with different processing performances for the query processing, upon execution of the query processing on input data received via the input data reception unit, estimates a performance value based on an amount of the unprocessed input data, determines, based on the estimated performance value, the execution system satisfying the requested performance value, executes the query processing by making by the determined execution system, and outputs processing results as output data to the data transmission unit. 
         [0012]    Specifically, to achieve the object described above, in best modes of the invention, for each calculation execution system used in query processing, an amount of data in a queue, a calculation time, and processing accuracy at this point are evaluated. Moreover, final processing accuracy with a set of calculation systems is also evaluated. This evaluation may be performed beforehand or may be accumulated during execution. Then during the execution, when the amount of data in the queue increases for some reason and is likely to become greater than requested latency, a change to a set of calculation systems that reduces the latency within a range permitting final quality is made. Conversely, in a case where the latency is likely to become greatly smaller than the requested latency while the accuracy is reduced, a change to a set of calculation systems with high processing accuracy is made. 
       Advantageous Effects of Invention 
       [0013]    According to an aspect of the invention, a stream data processing technology can be provided which is capable of selecting calculation contents considering latency and quality of the entire processing and satisfying user requests on the entire system. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0014]      FIG. 1  is a diagram showing one example of configuration of computer environment using a stream data processing server according to a first embodiment. 
           [0015]      FIG. 2  is a diagram showing one example of configuration of the stream data processing server according to the first embodiment. 
           [0016]      FIG. 3  is a diagram showing one example of performance guarantee software capability in a stream data processing system according to the first embodiment. 
           [0017]      FIG. 4  is a diagram showing one example of data processing definition according to the first embodiment. 
           [0018]      FIG. 5  is a diagram showing one example of a function including a plurality of execution systems used in the data processing definition shown in  FIG. 4 . 
           [0019]      FIG. 6  is a diagram showing one example in which a plurality of execution systems are arrayed in one function according to the first embodiment. 
           [0020]      FIG. 7  is a diagram showing one example of execution results of the respective execution systems of  FIG. 6  acquired by an execution result acquisition unit. 
           [0021]      FIG. 8A  is a diagram showing one example of queue capacity and a requested performance value of input data according to the first embodiment. 
           [0022]      FIG. 8B  is a diagram showing one example of performance values estimated based on the queue capacity and execution results held by the execution result acquisition unit according to the first embodiment. 
           [0023]      FIG. 8C  is a diagram showing one example of judgment by a latency evaluation unit on whether or not to apply the execution systems according to the first embodiment. 
           [0024]      FIG. 9  is a diagram showing a flow chart showing operation of switching the execution system in the stream data processing system according to the first embodiment. 
           [0025]      FIG. 10  is a diagram showing one example of execution systems of a plurality of functions in a stream data processing system according to a second embodiment. 
           [0026]      FIG. 11  is a diagram showing a flow chart showing operation of selecting the effective execution system in the stream data processing system according to the second embodiment. 
           [0027]      FIG. 12  is a diagram showing one example of a set of the selected effective execution systems according to the second embodiment. 
           [0028]      FIG. 13  is a diagram showing one example of results of evaluation on the effective execution systems of a plurality of functions according to the second embodiment. 
           [0029]      FIG. 14  is a diagram showing one example of execution system switching periods in the stream data processing system according to the second embodiment. 
           [0030]      FIG. 15A  is a diagram showing one example of queue capacity, requested performance, and requested accuracy according to the second embodiment. 
           [0031]      FIG. 15B  is a diagram showing one example of performance values estimated based on the queue capacity, the held execution results, and the execution system switching periods according to the second embodiment. 
           [0032]      FIG. 15C  is a diagram showing one example of judgment on whether or not to apply the execution systems according to the second embodiment. 
           [0033]      FIG. 16  is a diagram showing a flow chart showing execution system switching operation in view of the requested accuracy and the execution system switching period according to the second embodiment. 
           [0034]      FIG. 17  is a diagram showing one example of record of the execution system switching clock times according to the second embodiment. 
           [0035]      FIG. 18  is a diagram showing one example of GUI (Graphical User Interface) for setting the requested performance and the requested accuracy according to the second embodiment. 
       
    
    
     DESCRIPTION OF EMBODIMENTS  
       [0036]    Hereinafter, embodiments of the present invention will be described in detail based on the drawings. In all the drawings for illustrating the embodiments, the same members are basically provided with the same numerals and their repeated description will be omitted. Moreover, in this specification, a program executed by, for example, a computer forming a processing server that executes stream data processing, that is, query processing on inputted stream data may be called, for example, “capability”, “means”, or “unit”. For example, capability of an execution method determination program is called “execution system determination function”, “execution system determination means”, or “an execution system determination unit”. 
       First Embodiment 
       [0037]    First, referring to  FIGS. 1 and 2 , basic configuration of a system executing stream data processing according to the first embodiment will be described. 
         [0038]    As shown in  FIG. 1 , in the system executing the stream data processing, to a network  104 , a stream data processing server  100 , computers  101 ,  102 , and  103  are connected. The stream data processing server  100  receives, via the network  104 , data  108  from the computer  102  where a data source  107  operates, and transmits data  110  as processing results to a result-using application  109  on the computer  103 . Moreover, on the computer  101 , a query registration command execution interface  105  for registering a query for the stream data processing operates. Any two or three of these computers  101 ,  102 , and  103  can be formed by one computer or may be integrated into the stream data processing server  100 . 
         [0039]    As shown in  FIG. 2 , the stream data processing server  100  is composed of a computer  200 , which is composed of: a memory  202  as a storage unit, a central processing unit (CPU)  201  as a processing unit, a network interface (I/F)  204 , a storage  203  as a storage unit, and a bus  205  coupling them together. Arranged on the memory  202  is a stream data processing system  206  that defines logic operation of the stream data processing. The stream data processing system  206  is an execution image that can be interpreted by the CPU  201  as described in detail below. 
         [0040]    As shown in  FIG. 2 , the computer  200  forming the stream data processing server  100  is connected to the network  104  outside via the network I/F  204  as the interface unit. The number of computers forming the stream data processing server  100  is not limited to one and may be a plural number, but configuration of one computer is illustrated here. 
         [0041]    When the computer  200  forming the stream data processing server  100  has received a query  106  defined by the user via the query registration command execution interface  105  that operates on the computer  101  connected to the network  104 , the stream data processing system  206  forms therein a query graph that permits execution of the stream data processing in accordance with this definition. Then when the computer  200  forming the stream data processing server  100  has received data  108  transmitted by the data source  107  that operates on the computer  102  connected to the network  104 , data processing is performed in accordance with this query graph, and result data  110  is generated and transmitted to the result-using application  109  that operates on the computer  103 . The storage  203  saves the stream data processing system  206  and also the query  106  once received. The stream data processing system  206  can load this definition from the storage  203  upon startup and form a query graph. 
         [0042]    The configuration of the stream data processing server of this embodiment described here is one example, and the number of computers is not necessarily one but it may be composed of a plurality of computers, the CPU  201  as the processing unit of the computer may be composed of two processors on the same computer, and further the two processors may be two calculation cores in one multicore CPU. In this specification, the server may be configured in any way as long as it includes at least the processing unit, the storage unit, and the interface unit. 
         [0043]      FIG. 3  is a diagram showing functional block configuration of software that executes a performance guarantee method of the stream data processing system according to the first embodiment. In the same figure, blocks formed by thick lines schematically show various kinds of software capabilities executed by the CPU  201  as the processing unit of the computer  200  and blocks formed by thin lines schematically show saving regions of various kinds of data formed on, for example, the memory  202  upon software execution. Moreover, the functional block configuration diagram of the software also serves as a diagram showing software functional block configuration of a stream data processing system according to the second embodiment, and as described below, it is to be noted that part of the functional blocks and data are not used in the first embodiment. 
         [0044]    In  FIG. 3 , the stream data processing system  206  includes: an input data reception unit  301  receiving the input data  108 ; a query reception and analysis unit  306  receiving and analyzing the query  106  defined by the user and an external definition function  305 ; a query execution work area  308  holding the query graph, operators, etc.; a query execution unit  302  executing a query based on the query execution work area  308  and the input data  108  in the query reception and analysis unit  306 ; a request input unit  312  to which a user request  309  composed of requested latency  310  as a requested performance value is inputted; and an output data transmission unit  304  outputting a query execution result  110 . 
         [0045]    In addition, the stream data processing system  206  includes: the request input unit  312  receiving the user request  309  composed of the requested latency  310 ; an execution system determination unit  313 ; an execution result acquisition unit  318  receiving from the input data receiving part clock time at which data was inputted and capacity of the queue  319  at that time, also receiving from the query execution unit  302  an execution system of a function used upon processing of this data, receiving from the output data transmission unit  304  passage clock time at which this processed data was outputted, measuring latency based on difference between the clock time at which the data was outputted and clock time at which the data was inputted, and recording the measured latency together with the capacity of the queue at this point and information of the used system; and the execution system determination unit  313  determining, based on the information recorded by the execution result acquisition unit  318 , a function that satisfies the user request  309  received by the request input unit  312 . 
         [0046]    Note that in this specification, the input data reception unit  301 , the output data transmission unit  304 , and further the request input unit  312  may be collectively called an interface unit, and this interface unit may be identical to an interface unit of  FIG. 2  but they are not necessarily identical to each other and this interface unit can be preferably a functional interface unit of the stream data processing system itself that operates on the stream data processing server  100 . 
         [0047]    Here, the queue  319 , the input data reception unit  301  holds unprocessed data of the stream data processing system  206 . Moreover, the query reception and analysis unit  306  includes an external definition function building-in unit  307  that builds the external definition function  305  in the query execution work area  308 . 
         [0048]    The query execution work area  308  includes operators  1  to  3  indicating respective processing contents. Here, the operator  1  further includes built-in functions  1 , which include methods  1 A,  1 B, and  1 C, and the operator  2  further includes built-in functions  2 , which include methods  2 A,  2 B, and  2 C. Here, the built-in functions  1 A,  1 B, and  1 C are a plurality of functions that perform the same calculation, but they have different calculation accuracy and calculation times in this embodiment. The same applies to the built-in functions  2 A,  2 B, and  2 C of the operator  2 . 
         [0049]    The query execution unit  302  according to this embodiment includes an execution system switching unit  303  that dynamically changes the system of the function to be used in query execution in accordance with the determination of the execution system determination unit  313 . Moreover, the execution system determination unit  313  includes: a latency estimation unit  314  which receives the capacity of the queue  319  from the input data reception unit and which estimates, based on past information recorded by the execution result acquisition unit  318 , latency when each system of the function is used; and a latency evaluation unit  315  that evaluates the usable system based on the estimation of the latency estimation unit  314  and the requested latency  310  of the user. 
         [0050]    Requested calculation accuracy  311  in the user request  309  and a calculation accuracy evaluation unit  316  and an effective method determination unit  317  in the execution system determination unit  313 , which are shown in  FIG. 3  are portions related to the second embodiment, and they will be described in detail below and thus their description is omitted here. 
         [0051]    Next, referring to  FIGS. 4 and 5 , one example of query processing in the stream data processing of this embodiment will be described.  FIG. 4  is a diagram showing one example of data processing definition, and as shown in the same figure, data processing definition  400  is a query that defines two input streams sa and sb and three queries q 1 , q 2 , and q 3 . Numeral  500  of  FIG. 5  is a diagram showing one example of a function including a plurality of execution systems used in the data processing definition shown in  FIG. 4 . The query reception and analysis unit  306  of the stream data processing system  206  shown in  FIG. 3  receives and analyzes the query shown in  FIG. 4  and builds in a necessary external definition function. The data processing definition  400  and a function example  500  shown in  FIGS. 4 and 5  are just one example, and not limited to this example. 
         [0052]    Subsequently, referring to  FIG. 6 , a plurality of calculation system for each function described above in the stream data processing system of this embodiment will be described. Numeral  600  of  FIG. 6  is a table which is provided for the stream data processing system of this embodiment to execute a predetermined function and which holds calculation times corresponding to a plurality of execution systems. In the same figure, as one example of the plurality of systems for a predetermined function, an example of a function sin is illustrated. In the same figure, the methods a, b, and c respectively have the calculation times: short, intermediate, and long. 
         [0053]      FIG. 7  is a diagram in a graph showing one example of execution results of the respective execution systems acquired and held by the execution result acquisition unit  318 . In correspondence with the function sin calculation systems a, b, and c shown in  FIG. 6 , amounts of calculation data are plotted at a horizontal axis and the calculation times are plotted at a vertical axis. In the same figure, a solid line shows the execution results of the method a, a two-dot chain line shows the execution results of the method b, and a broken line shows the execution results of the method c. 
         [0054]    In the stream data processing system  206  of this embodiment shown in  FIG. 3 , as described above, the execution system determination unit  313 , based on the information acquired and held by the execution result acquisition unit  318 , determines the function that satisfies the user request  309  as the requested performance value received by the request input unit  312 . The execution system switching unit  303  of the query execution unit  302 , in accordance with the determination of the execution system determination unit  313 , dynamically changes the system of the function used in the query execution. Moreover, the latency estimation unit  318  of the execution system determination unit  313  receives the capacity of the queue  319  of the data  108  from the input data reception unit  301 , and estimates, based on the past information recorded by the execution result acquisition unit  318 , latency when each system of the function is used, and the latency evaluation unit  315  evaluates the usable system based on the estimation of the latency estimation unit  314  and the requested latency  310 . 
         [0055]    Specifically, in the execution system determination unit  313  of the stream data processing system  206 , clock time at which the data was inputted and the capacity of the queue  319  at that time are received from the input data reception unit  301 , also the execution system of the function used upon processing of this data is received from the query execution unit  302 , and passage clock time at which this processed data is outputted is received from the output data transmission unit  304 . Then the execution result acquisition unit  318  measures latency based on difference between clock time at which this data was outputted and clock time at which it was inputted, and records the measured latency together with the capacity of the queue and the used system at this point. Then the execution system determination unit  313 , based on the information held by the execution result acquisition unit  318 , determines the function that satisfies the user request  309  received by the request input unit  312 . 
         [0056]    Numeral  800  of  FIG. 8A  shows one example of queue capacity given to the execution system determination unit  313  by the input data reception unit  301  and a requested performance value given by the request input unit  312 . Here, the requested performance value shows requested latency. Similarly, numeral  801  of  FIG. 8B  shows one example of performance values estimated based on the queue capacity given to the latency estimation unit  314  and the execution results held by the execution result acquisition unit  318 . Here, the estimated performance values show calculation times required for the respective execution systems. Moreover, numeral  802  of  FIG. 8C  shows one example of evaluation results obtained after evaluation by the latency evaluation unit  315  on whether or not the execution system is applicable. 
         [0057]    Specifically, as shown in  FIGS. 8A ,  8 B, and  8 C, in a case where the data capacity of the queue  319  is 10000, the requested latency  310  from the user is 40 ms, and the calculation times of the systems a, b, and c are 14 ms, 40 ms, and 60 ms, the systems a and b are determined to be applicable and the system c is determined to be not applicable. These pieces of data are acquired by the execution result acquisition unit  318  of  FIG. 3  and held therein and in other parts. 
         [0058]      FIG. 9  is a flow chart showing operation of dynamically switching a plurality of execution systems performed by the execution system determination unit  313  and the query execution unit  302  of the stream data processing system  206  of this embodiment. First, in a case where there is a change in the queue capacity of the data  108  inputted to the input data reception unit  301 , a processing flow starts (step  900 , hereinafter step is omitted in brackets). 
         [0059]    The execution system determination unit  313  judges whether or not there is any problem with the latency ( 901 ). If there is no problem with the latency (N), it is judged whether or not there are measurement results of the plurality of systems in the execution result acquisition unit  318  ( 902 ), and if there is any problem (Y), the processing ends ( 910 ). 
         [0060]    If there are measurement results of the plurality of systems (Y), the effective system that satisfies the requested latency is subsequently searched ( 903 ). As a result, if there is the effective system (Y), this effective system is changed ( 905 ), and the processing ends ( 910 ). If there is no effective system, an error is outputted ( 906 ) and the processing ends ( 910 ). 
         [0061]    In step  902 , if there are no measurement results of all the systems (N), it is checked whether or not system tendency information is stored in the execution result acquisition unit  318 , etc. beforehand ( 907 ), and if there is system tendency information, from this system tendency information, the system that can solve the current problem is selected and system switching change is performed ( 908 ). If there is no tendency information, in this embodiment, random selection is made from the unmeasured systems and a change is executed ( 909 ). Note that this system tendency information can be held in, for example, the execution result acquisition unit  318  when necessary at time of system configuration. 
         [0062]    It is also possible to configure the execution system determination unit  313  of the stream data processing system, which is executed on the CPU as the processing unit of this embodiment, in a manner such as to make determination to switch the execution system upon increase in the amount of the unprocessed input data in a state in which the acquired performance value exceeds the requested performance value. Moreover, needless to say, it is also possible to provide configuration such that the past performance values held in the execution result acquisition unit  318  and the amount of the unprocessed input data are compared to each other and switching to the execution system that satisfies the requested performance value is determined. 
         [0063]    According to the stream data processing system of the first embodiment described above in detail, based on the amount of data received by the system, with the estimated latency as an index, the execution system for calculation on the received data can be switched and selected, making it possible to guarantee latency while ensuring real time property. 
       Second Embodiment 
       [0064]    Subsequently, as the second embodiment, a stream data processing system capable of guaranteeing not only latency but also processing accuracy will be described. Note that in the description of this embodiment, portions in common with those in the description of the first embodiment will be omitted from the description. Configuration of computer environment used by a stream data processing server of this embodiment and configuration of the stream data processing server are the same as those of  FIGS. 1 and 2 , and thus they will be omitted from the description here. 
         [0065]    As described in the description of  FIG. 3 , in the performance guarantee software functional diagram in the stream data processing of  FIG. 3 , there are data and capability used only in this embodiment. That is, in  FIG. 3 , included in the user request  309  is, in addition to the requested latency  310 , requested calculation accuracy  311  as requested accuracy used only in this embodiment. Included in the execution system determination unit  313  are: in addition to the latency estimation unit  314  and the latency evaluation unit  315 , the calculation accuracy evaluation unit  316  and the effective method determination unit  317  used in this embodiment. 
         [0066]    In this embodiment, the execution system determination unit  313  evaluates, in addition to the capabilities of the previous first embodiment, output data and measures calculation accuracy, and the execution result acquisition unit  318  records and holds the measured latency and the calculation accuracy together with the queue capacity and information of the used system at that point. Then based on the information recorded and held by the execution result acquisition unit  318 , the execution system of one or a plurality of functions that satisfy the user request  309  received at the request input unit  312  is determined. 
         [0067]    Here, also in this embodiment, the execution system switching unit  303  of the query execution unit  302 , in accordance with the determination of the execution system determination unit  313 , dynamically changes the system of the function used in the query execution. Moreover, the execution system determination unit  313 , as is the case with the first embodiment, newly includes: in addition to the latency estimation unit  314  that receives the capacity of the queue  319  the input data reception unit and estimates, based on past information recorded by the execution result acquisition unit  318 , latency when each system of the function is used and the latency evaluation unit  315  that evaluates the usable system based on the estimation of the latency estimation unit  314  and the requested performance  309  of the user, as described above, a calculation accuracy evaluation unit  316  that evaluates the system satisfying the requested calculation accuracy  311  based on the information recorded by the execution result acquisition unit  318 ; and an effective method determination unit  317  that determines a set of effective systems when a plurality of built-in functions are used on the query execution work area  308 .  FIG. 10  shows one example of the execution systems of the plurality of functions by the latency evaluation unit and the calculation accuracy evaluation unit according to this embodiment. (a) and (b) of  FIG. 10  correspond to the function sin and the function cos, respectively. The systems a, b, and c respectively correspond to systems α, β, and γ, and as is the case with  FIG. 6 , the calculation times: short, intermediate, and long and their accuracy are obtained and held. In the same figure, the accuracy is indicated in index indication. 
         [0068]      FIG. 11  is a diagram showing a flow chart showing operation of selecting a set of effective systems by the execution system determination unit  313  when a plurality of built-in functions are used on the query execution work area  308 . In the same figure, the plurality of existing functions are sequentially reviewed as sets of functions I and functions J (I, J, and K are natural numbers of  1  or above). That is, of installation systems of the functions J, the installation method whose calculation accuracy is better than that of the installation system K and whose calculation time is shortest among them is selected ( 1103 ). This processing is executed for all the functions J excluding the functions I ( 1102 ,  1104 , and  1105 ), is executed for all the installation systems K excluding the functions I ( 1101 ,  1106 , and  1107 ), is executed for all the functions I ( 1100 ,  1108 ,  1109 ), and then the processing ends. 
         [0069]    Numeral  1200  of  FIG. 12  is a diagram showing one example of sets of effective execution systems selected and held as a result of the selection processing in the second embodiment as described above. The set i, ii, iii, iv, and v respectively correspond to accuracies shown, and the function set shown in columns of the function  1  and the function  2  is consequently selected. 
         [0070]      FIG. 13  is a diagram in a graph showing one example of results of evaluation by the latency evaluation unit  315  of this embodiment shown in  FIG. 12  for the sets of the effective execution system for a plurality of functions. The calculation time increases with an increase in accuracy. 
         [0071]      FIG. 14  is a diagram showing one example of execution system switching times in the stream data processing system of the second embodiment. The switching times are also held in, for example, the execution result acquisition unit  318 . The same figure shows the switching times increase as the accuracies improve. 
         [0072]      FIG. 15A  shows one example of the queue capacity given to the execution system determination unit  313  by the input data reception unit  301  and the requested performance value and the requested calculation accuracy given by the request input unit  312 ,  FIG. 15B  show one example of the queue capacity given to the latency estimation unit  314 , the execution results held by the execution result acquisition unit  318 , and the performance values estimated based on the execution system switching times, and  FIG. 15C  shows one example of judgment by the latency evaluation unit  315  and the calculation accuracy evaluation unit  316  also considering the switching times on whether or not the execution systems are applicable. In the example shown in  FIG. 15C , it is judged that the system ii and the system iii are applicable in terms of the total time and the accuracy, and it is judged that the remaining three systems are not applicable. 
         [0073]      FIG. 16  is a diagram showing a flow chart showing operation of switching the execution system by the execution system determination unit  313  and the query execution unit  302  in view of even the requested accuracy and the execution system switching time according to this embodiment. In the same figure, as is the case with the flow chart of  FIG. 9 , when there is a change in the queue capacity of the data  108  inputted to the input data reception unit  301 , the processing flow first starts ( 1600 ). 
         [0074]    The execution system determination unit  313  judges whether or not there is any problem with both the latency and the accuracy ( 1601 ). If there is any problem (Y), it is checked whether or not there is an instruction to reduce the latency as much as possible ( 1602 ). If there is such an instruction, the processing ends ( 1611 ). 
         [0075]    If there is no instruction to reduce the latency as much as possible (N), or if there is no problem with both the latency and the accuracy (N), it is judged whether or not there are already measurement results of the plurality of system ( 1603 ). 
         [0076]    If there are measurement results of the plurality of systems (Y), the effective system that satisfies both the requested latency and the accuracy is searched while the switching time is added ( 1604 ,  1605 ). As a result, if there is any effective system (Y), a change to the effective system is made ( 1606 ) and the processing ends ( 1611 ). If there is no effective system, an error is outputted ( 1607 ) and the processing ends ( 1611 ). 
         [0077]    In step  1603 , if there are no measurement results of all the systems (N), as is the case with the first embodiment, it is checked whether or not system tendency information is stored ( 1608 ), and if there is any system tendency information, from this system tendency information, the system that solves the current problem is selected and a change is made ( 1609 ). If there is no tendency information, random selection from the unmeasured systems is made and a change is executed ( 1610 ). 
         [0078]    In this embodiment, in a case where there are sets of a plurality of execution systems to be switched by one or the plurality of operators of the query processing, with reference to the calculation accuracy of output data, it is also possible to provide configuration such that a set of execution methods having highest performance with the calculation accuracy is determined. That is, in a case where there is a switching point (function) of the plurality of execution systems in the stream data processing, their respective calculation performances and calculation accuracies may be evaluated and the most effective set may be selected. 
         [0079]      FIG. 17  shows one example of recording of the execution system switching time acquired and held by the execution result acquisition unit  318  of the stream data processing system of the second embodiment. As is clear from the same figure, identification information of the sets and their corresponding switching times are held. Data holding of the switching times of this figure is not limited to the second embodiment, but is also preferably used in the first embodiment. However, it is needless to say that in the first embodiment, the identification information of the sets is replaced with the identification information of the execution systems and the switching times. 
         [0080]      FIG. 18  shows one example of a graphical user interface (GUI) that sets the requested performance and the requested accuracy in this embodiment. It is needless to say that a similar GUI can also be used in the system of the first embodiment, in which case it is needless to say that there is no need of displaying an accuracy setting portion. 
         [0081]    In the same figure, in correspondence with the second embodiment, displayed on a GUI screen  1800  is a requested performance and accuracy setting screen. It is needless to say that a device displaying such a display screen can be usually realized by use of a normal display device and image display software. On the GUI setting screen of  FIG. 18 , selection from “Enable execution system automatic selection capability”, “Make selection in a manner such that latency does not exceed specified value”, “Make selection in a manner such that accuracy of output data maintains requested accuracy”, etc. can be made by providing a mark at a check unit  1803  shown. Moreover, it is needless to say that the requested latency and the requested calculation accuracy can be made possible by appropriately inputting desired numerical values from the screen. Numerals  1802  and  1803  indicate carry out optimization and set instruct buttons, respectively. 
         [0082]    With the stream data processing system of the second embodiment described above in detail, based on the amount of data received by the system, with the estimated latency and the calculation accuracy as indices, the execution system of calculation for the received data can be switched and selected, making it possible to guarantee the latency and the processing accuracy while guaranteeing real-time property. 
         [0083]    The various embodiments of the present invention have been described above, but the present invention is not limited to them, and it is needless to say that various modified embodiments are included. The embodiments described above are for better understanding of the invention, and the invention is not limited to them. Moreover, it is also possible to replace part of configuration of certain embodiment with configuration of the other embodiment, and it is also possible to add the configuration of the other embodiment to the configuration of the certain embodiment. For example, it is needless to say that the switching method taking the execution system switching time into consideration, which has been described in the second embodiment, can be applied to the first embodiment. Moreover, it is needless to say that the configuration, the capabilities, the processing, etc. of the embodiments described above can be realized as not only software configuration described as part or whole of them but also as special hardware configuration or configuration sharing them. 
       INDUSTRIAL APPLICABILITY  
       [0084]    The present invention is extremely useful as stream processing technology intended to guarantee latency and further processing accuracy in a stream data processing field. 
       REFERENCE SINGS LIST 
       [0000]    
       
           100  Stream processing server 
           101 ,  102 ,  103 ,  200  Computer 
           104  Network 
           201  CPU 
           202  Memory 
           203  Storage device 
           204  Network I/F 
           205  Internal bus 
           206  Stream data processing system 
           301  Input data reception unit 
           302  Query execution unit 
           303  Execution system switching unit 
           304  Output data transmission unit 
           305  External definition function 
           306  Query reception and analysis unit 
           307  External definition function building-in part 
           308  Query execution work area 
           309  User request 
           310  Requested latency 
           311  Requested calculation accuracy 
           312  Request input unit 
           313  Execution system determination unit 
           314  Latency estimation unit 
           315  Latency evaluation unit 
           316  Calculation accuracy evaluation unit 
           317  Effective system determination unit 
           318  Execution result acquisition unit 
           319  Queue 
           1800  GUI screen 
           1800  Carry-out optimization execute button 
           1800  Setting execute button