Distributed Data-base Communication System

Abstract: A distributed data-base communication network system includes a plurality of terminal stations (12a, 12b, 12c) which respectively contain data-base devices (15) and which are associated with one another by means of data communication lines (14). A data-base management apparatus (16) is provided in each of these stations and includes an internal load monitor device (20) for monitoring the accessing load of the internal data-base device (15) of the internal station (12a) and an external load monitor device (24) for monitoring the accessing loads of the data-base devices of the external terminal stations (12b, 12c). A data-base load distribution management device (28) is connected to the monitor devices (20, 24), and automatically transfers at least part of the data-base information of the internal data-base device to a selected one (12c) of the external terminal stations when the internal data-base accessing load has exceeded the maximum permissible level, thus enhancing the uniformity of distribution of the data-base load of the communication network system.

Description: The present invention relates to a communication system for digital data distribution including terminal stations or work stations connected to one another by means of digital data transmission lines, and more particularly to a data-base management architecture for such a system. Recently, a distributed data communication network system has received much more attention in place of a centralized data communication network system. In the centralized data communication network system, a host computer is used to control/manage data communication between work stations associated therewith. In contrast, in the distributed data communication network system, a distributed data-base management device is provided in each of the work stations, which controls data communication between the terminal station containing this management device and a terminal station or stations associated therewith. Therefore, each terminal may effect mutual data communication with a desired destination terminal independently of the other terminals. A data-base network system can be given as one example of systems which most positively adopt the concept of data communication network. In this case, an internal data-base unit is provided in each of local work stations subscribed to the data-base system. The data-base unit can be freely accessed by not only the station (self station) containing the data-base unit but also any one of the remaining stations (external stations). In this sense, it is safe to say that information of the data-base unit of each station can be shared as the common information source by all the stations subscribed to the system. In the conventional distributed data communication network system, however, it is extremely difficult to effectively perform the mutual access to data-base at a high response speed. One of the important reasons is that the data-base accessing load between the stations is not uniform. More specifically, when accessing requests of a number exceeding the load permissible level for the data-base of a certain work station are supplied from the other stations to the data-base of the certain work station, for example, it becomes impossible to effect rapid data communication therebetween. Particularly, in the conventional system, only one measure can be taken to cope with the above difficulty, and in this case, the operator uses a predetermined software command of an operating system to transfer at least part of data-base information of the certain station to another station whose load is now relatively small, thus distributing the data-base load. With such a manual load distribution management, it is almost impossible to fully cope with the continual change of the accessing load of the data communication. It is therefore an object of the present invention to provide a new and improved distributed data-base managing architecture which can be preferably applied to a distributed data-base system to automatically and adequately effect the load distribution of data-base devices provided at sites, thus attaining effective data-base accessing. We acknowledge the disclosure in "Computer", vol. 17, no. 1, January 1984, pages 23-32, IEEE, Long Beach, CA, US; B.W. Wah: "File placement on distributed computer systems" of a technique for moving data files between stations on the basis of frequency of access to those files. The present invention provides a distributed database communication system as defined in Claim 1. The present invention and its objects and advantages will become more apparent in the detailed description of a preferable embodiment presented below by way of example only, with reference to the accompanying drawings, of which: Fig. 1 is a diagram schematically showing the entire construction of a distributed data-base communication network system according to a preferable embodiment of the present invention; Fig. 2 is a block diagram showing the internal structure of each of work stations of Fig. 1; Figs. 3 to 5 are model graphs showing the monitoring results obtained by monitor devices shown in Fig. 2; and Figs. 6A and 6B are a flowchart showing the automatic data-base distribution management process effected by a load distribution management unit shown in Fig. 1. Referring now to Fig. 1, a distributed data-base communication network system according to a preferable embodiment of the present invention is generally designated by a reference numeral "10", wherein a plurality of terminal stations 12 are connected to one another by means of respective exclusive communication lines such as digital data transmission lines. The terminal stations 12 may be variously referred to as "data-base stations", "work stations", "subscriber stations", "local stations" or "sites"; in this description, the term "work stations" is used as a common name of these terminal stations. It should be noted that, although only three work stations 12a, 12b and 12c are illustrated in Fig. 1 simply for brevity of the drawing, a larger number of work stations may be incorporated into this system as required. As shown in Fig. 1, each of the work stations 12a, 12b and 12c is independently connected to the remaining ones of the work stations 12 via digital data transmission/communication lines 14a, 14b and 14c. For example, the work station 12a is connected to the work station 12b via the data communication line 14a, and at the same time connected to the work station 12c via the data communication line 14b. With this connection, any one of the work stations can be freely communicated with the other work stations associated therewith. As shown in Fig. 2, each of the work stations 12 includes data-base section 15 and data-base/data communications control section 16. The data-base section 15 may be a programmable data storage device of a large capacity functioning as a data bank. A magnetic fixed disk memory device, optical disc memory device or the like may be preferably utilized to constitute the data-base device. The control section 16 is connected to the data-base section 15 and includes a data-base management unit 18 for managing the transfer data and memory address in the data accessing operation of the data-base section 15. The data-base management unit 18 is connected to four monitoring devices 20, 22, 24 and 26, and a load distribution management unit 28. The load distribution management unit 28 is connected to a distributed processing control unit 30 for performing the distribution access control in the operation of exchanging data between the internal work station and the external work stations. Each of the stations 12 effects data exchange with the other work stations via the distributed processing controller 30. In the system of Fig. 1, the explanation is further made assuming that the work station 12a takes a leading role in the system. For convenience, the station 12a is hereinafter referred to as an "self station". The monitor 20 functions as an internal load monitor for monitoring, on the real time base, the current access load of the data-base section 15 of the self work station 12a in which it is arranged. The monitor 22 is a table data monitor for monitoring table data of the data-base section 15. The monitor 24 is an external load monitor for monitoring the current access load of each of the other work stations 12b and 12c associated with the work station 12a on the real time base. The monitor 26 functions as a traffic monitor for monitoring the current traffic on the data communication lines 14 between the self station 12a and the other stations 12b and 12c on the real time base. The load distribution management unit 28 selects or determines part of information stored in the data-base section 15 to be transferred and a target work station to which the selected part of information is transferred based on the monitor information of the monitors 20, 22, 24 and 26. The data-base management unit 18 reads out or writes table data transferred between the self work station 12a and the other work station or work stations from or into the data-base section 15 in response to the determination made by the load distribution management unit 28. The result of the monitoring operation of the internal load monitor 20 is shown in Fig. 3 wherein the abscissa of the graph indicates time and the ordinate thereof indicates the load of the internal station. As is clearly seen from the graph, the load (which is hereinafter referred to as an "internal load") 40 of the self station 12a continually changes and the accessing to the data-base resources of the station 12a overflows when the load exceeds the maximum permissible level indicated by a broken line 42. At this time, an allocation queue occurs. The result of the monitoring operation of the external load monitor 24 is shown in Fig. 4. In the graph of Fig. 4, a solid line 44 indicates variation in the load of another station 12b, whereas a solid line 46 indicates variation in the load of the other station 12c. The maximum permissible level commonly set for the stations 12b and 12c is indicated by a broken line 48. In general, the maximum permissible level is set at the same level as the level 42. The external load monitor 24 provided in the self station 12a receives internal load monitoring results supplied from the internal load monitors 20 of the work stations 12b and 12c in real time, and uniformly manages them as "external loads". Since the internal load monitor 20 and external load monitor 24 are arranged in each work station 12, the current load conditions of the internal load and the external loads can be easily determined in any one of the work stations 12. The result of the monitoring operation of the traffic monitor 26 of the self station 12a is shown in Fig. 4, wherein solid lines 50a, 50b and 50c indicate variations in the traffics on the data communication lines 14a, 14b and 14c between the work stations. The maximum permissible traffic level of the data communication lines 14a, 14b and 14c is shown by a broken line 52. In this example, the maximum permissible traffic level of each data communication line is set at the same level as those of the remaining data communication lines. Data of the monitoring result of the table data monitor 22 of the self station 12a is shown in the following table. The table data monitor 22 monitors continually changing service conditions of table data, for example, table data A1, A2 and A3, of the data-base section 15 of the self station 12a in which it is arranged, and stores updated monitoring results therein. For example, in the above Table, it is shown that the table data A1 has been accessed five times by the self station 12a and no access request from the external stations has occurred. Such an access condition can be rapidly informed by consulting the table data monitor 22. The monitor 22 further monitors the service conditions of table data for respective internal and external stations. For example, if the table data A2 has been accessed once by the self station 12a, accessed seven times by the external station 12b, and accessed two times by the external station 12c, then the monitoring result data of the table data monitor 22 clearly indicates that the data A2 has been accessed once by the self station 12a and accessed nine times in total by the external stations 12b and 12c as shown in the right side columns of the above Table. In this way, history information relating to which of the work stations 12 has generated a transaction which requires use of the table data and the number of times by which the table data has been used to date can be easily obtained by means of the table data monitor 22. Now, the operation mode of the embodiment of the above construction is explained with reference to the flowchart shown in Figs. 6A and 6B. The load distribution management unit 28 of the work station 12a inspects the internal data-base accessing load condition of the station 12a at a step 60 and checks at a step 62 whether or not the internal load is below the maximum permissible level 42 (see Fig. 3). If it is detected that the internal load is within the allowable range as the result of consultation with the internal load monitor 20, the management operation is returned to the step 60. If it is determined that the internal load is outside the allowable range, that is, the internal load of the self station 12a has exceeded the maximum permissible level 42 (overloaded), it consults with the external monitor 24 at a step 66 to inspect the load condition (external load condition) of the external stations 12b and 12c. At the step 66, it is checked whether or not a station having a load less than that of the self station 12a is present in the external stations 12b and 12c. If there is no such an external station, the operation is returned to the step 60. In contrast, if such an external station or external stations are detected, the load distribution management unit 28 determines that part (table data) of the stored information of the data-base section 15 of the internal station 12a should be transferred to a detected one of the external stations. At this time, the table data to be transferred is determined based on information from the table data monitor 22 by the load distribution management unit 28 in the following manner. That is, at a step 70, the load distribution management unit 28 consults with the table data monitor 22 to check whether or not table data whose access-frequency (frequency in use) by the external stations 12b and 12c is higher than the access-frequency by the self station 12a is included in the table data items of the data-base of the self station 12a. If there is no such a table data, the operation is returned to the step 60. In contrast, if such a table data is detected, the load distribution management unit 28 determines at the step 72 that such a table data should be transferred to the exterior. For example, in a case where the monitor data of the table data monitor 22 is set in such a condition as shown in the above presented Table, the frequency in use (frequency in internal use) by the self station 12a which is "1" is smaller than the frequency in external use which is "9" only in the case of the table data A2 among the table data A1, A2 and A3 of the self station 12a. Therefore, in this case, the load distribution management unit 28 selects the table data A2 as data to be transferred. Subsequently, at a step 74, the load distribution management unit 28 detects an external station which has used the selected table data most frequently. In this example, the station 12b is detected. This is because the station 12b has used the table data A2 of the station 12a most frequently (seven times) as shown in the above presented Table. At a step 76, monitor information of the table data monitor 22 is used in order to determine whether the load of the detected station 12b is within the allowable range or not. If the load of the detected station 12b is within the allowable range, the load distribution management unit 28 determines the station 12b as a "target station" to which the table data A2 is transferred. However, in this example, since the load of the external station 12b has exceeded the maximum permissible load level 48 as shown by the solid line 44 in Fig. 4, the load distribution management unit 28 immediately comes to recognize that the load of the station 12b is outside the allowable range. Therefore, in this case, at a step 80, the load distribution management unit 28 will determine that one of the remaining external stations which has the smallest load as the target station. After the table data A2 to be transferred and the target station 12c have been determined as described above, the load distribution management unit 28 determines the transfer route. More specifically, the load distribution management unit 28 examines monitor information obtained from the traffic monitor 26 at a step 82 and checks at a step 84 whether the current traffic of the communication line 14b from the self station 12a to the target station 12c is below the maximum permissible traffic level or not. If "YES" in the step 84, data transfer is effected at a step 86. If "NO" in the step 84, the load distribution management unit 28 effects the operation of the step 82 again to examine another transfer route. The data transfer route from the station 12a to the station 12c includes two routes; one being given by the communication line 14b which directly connects the stations 12a and 12c to each other and the other being given by the communication lines 14a and 14c which connect the stations 12a and 12c to each other via the station 12b. Therefore, if the traffic on the communication route along the communication lines 14a and 14c is within the allowable range, then it is possible to select the communication route. Further, there are some cases wherein none of the communication routes which can be formed between the stations 12a and 12c are available. In such a case, the load distribution management unit 28 will repeatedly effect the above described communication route determination process. With such an arrangement, the process of uniformly distributing the detected load and detecting the occurrence of the overload of the data-base access in the data-base communication network system 10 can be automatically and efficiently effected by means of the load distribution management unit 28 which cooperates with the four monitors 20, 22, 24 and 26. In particular, since, in each work station 12, the load condition of not only the internal load thereof but also the load of the external stations 12b and 12c associated therewith can be rapidly and precisely detected by means of the external load monitor 24, the target station can be rapidly determined. Further, since that one of the table data in the data-base information of the self station 12a which should be selected as table data to be transferred is determined according to the monitor information in such a manner as to automatically derive the table data which has been most frequently used, the uniformity of distribution can be held at the maximum level. Since the data transfer route to the selected "target station" is determined so as to contain as many communication lines whose traffics are relatively small as possible, the communication cost of the data transfer for distribution between the stations can be reduced. The "automatic data-base distribution management" concept of this invention may be applied to various types of data-base systems such as a relational data-base communication system and a knowledge base communication system. Further, the management operation of the load distribution management unit 28 is not limited to that shown in Figs. 6A and 6B, and the detail thereof can be freely modified so as to meet the practical applications.

Claims: A distributed data-base communication system (10) comprising a plurality of terminal stations (12a, 12b, 12c) respectively including data-base devices (15), communication lines (14a, 14b, 14c) for connecting said stations to one another so as to permit each of said stations to independently communicate with a desired one of said stations, and control devices (16) provided in said terminal stations, characterized in that each of said control devices comprises: internal load monitor means (20) for monitoring the load of internal data-base accessing required by the corresponding self station (12a) to which said internal load monitor means belongs, external load monitor means (24) for monitoring the loads of external data-base accessing required by external stations (12b, 12c) associated with said self station (12a), and load distribution management means (28) connected to said internal load monitor means (20) and said external load monitor means (24), for automatically transferring at least part of table data stored in said data-base device (15) of said self station to at least one of said external stations (12b, 12c) when the data-base accessing load of said self station (12a) is detected to exceed the maximum permissible level based on the monitor information of said internal and external load monitor means, thus enhancing the uniformity of distribution of the data-base access load of said system. A system according to Claim 1, in which each of said control devices (16) further comprises: table data monitor means (22) for monitoring the history of accessing to said data-base device (15) of said self station (12a) by itself and by said external stations (12b, 12c). A system according to Claim 2, in which each of said control devices (16) further comprises: traffic monitor means (26) for monitoring a current traffic on each of said data communication lines (14a,14b,14c). A system according to Claim 3, in which said load distribution management means (28) is arranged in each of said terminal stations (12a, 12b, 12c). A system according to Claim 1, in which each terminal station further comprises: third monitor means (22) for monitoring the service condition of the data-base information of said internal data-base device (15) and for maintaining the history information thereof as monitor information; and said management means (28) is for at least partially specifying data-base information to be externally transferred based on the monitor information of said third monitor means. A system according to Claim 5, in which each said management means (28) is arranged to detect data-base information which is included in the data-base information of said data-base device (15) and which is accessed more frequently externally than internally and determines the detected data-base information as data to be transferred. A system according to Claim 6, further comprising: fourth monitor means (26) for monitoring the traffic on the communication lines between said terminal stations and for storing traffic monitoring information therein; and in which said management means is for determining a communication route which is actually used for transferring the data-base information to be externally transferred based on the traffic monitoring information. A system according to Claim 7, in which said management means (28) is arranged first to select a specific communication route from among a plurality of communication routes which each connect an internal station (12a) having said internal data-base device (15) which contains said data-base information to be externally transferred and a target station (12b) to which said data-base information is to be transferred to each other, said specific communication route directly connecting said internal station and said target station to each other. A system according to Claim 8, in which said management means (28) is arranged to select a second specific communication route from among said plurality of communication routes when said specific route is busy, said second specific communication route being constituted by communication lines which indirectly connect said internal station and said target station to each other and whose traffic is monitored by said fourth monitor means (26) of said stations and detected to be below a maximum permissible level. A system according to Claim 8, in which said management means (28) is arranged to attempt to designate the same specific communication route again after an elapse of a predetermined period of time when the specific communication route is busy. A system according to Claim 8, in which said management means (28) is arranged to identify that one of said external terminal stations which most frequently accesses the data-base information of said internal data-base device (15) to be transferred and determines the identified external terminal station as said target station.

Inventors: MORIMOTO YOJIRO INTELLECTUAL P, MURANAGA MIHO INTELLECTUAL PRO, SEKIGUCHI KOUICHI INTELLECTUAL, YAMASHITA YOSHIKAZU INTELLECTU, MORIMOTO, YOJIRO INTELLECTUAL PROPERTY DIVISION, MURANAGA, MIHO INTELLECTUAL PROPERTY DIVISION, SEKIGUCHI, KOUICHI INTELLECTUAL PROPERTY DIVISION, YAMASHITA, YOSHIKAZU INTELLECTUAL PROPERTY DIVISIO
Applicants: TOSHIBA KK, KABUSHIKI KAISHA TOSHIBA
Application year: 1989
Main classification: G06F17
IPC codes: G06F17, G06F9, G06F12, G06F15