Data processing: database and file management or data structures – Database design – Data structure types
Reexamination Certificate
1998-03-17
2001-06-05
Alam, Hosain T. (Department: 2172)
Data processing: database and file management or data structures
Database design
Data structure types
C707S793000
Reexamination Certificate
active
06243719
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a client/server distributed system, and in particular to a technique for improving the system response speed.
RELATED ART OF THE INVENTION
In typical client/server distributed systems, databases are provided on the server side and the application programs are provided on the client side. The server administrates the database stored on disk and responds to processing requests from clients. Access authorization for each client (for example, reference only, update capability, read and write capabilities, erase capability) is set on the server for each piece of data in the database. Then, when a database processing request is received from a client, the server checks the access authorization for the client, and if the processing request is allowed, carries out the requested processing on the database.
One application of client/server distributed systems is an electronic conference system, where an unspecified plurality of users exchange information. Electronic conference systems are usually described in terms of containers called forums. A forum contains actual information in the form of hierarchical messages. A user of an electronic conference system first sends a request from a client to the server requesting a listing of the messages contained in a certain forum. The server subsequently retrieves the messages contained in the specified forum from the database, creates a message list, and then returns this list to the client. The client receives and then displays this list of messages. When the user of the electronic conference system then selects a message from the displayed list, the database on the server is retrieved and the message displayed on the client.
However, because database access speed is generally slow, there is a time delay from when the user of the electronic conference system requests a listing of messages until the client actually displays the list of messages. Furthermore, after the list of messages has been displayed, there is further delay when the user then selects a message. That is, the response speed of the system depends on the access speed of the database.
Consequently, a technique has been proposed for improving the response speed of the system, wherein the results of database retrieval are cached periodically in a file on the server, and in those cases where the retrieval result for a database retrieval request is in the file, the cached retrieval result is returned to the client.
However, current application of this technique has the following type of problems.
(1) For databases which are updated regularly, there is a danger that the most recent information will not be returned to a client following a retrieval request. That is, because the retrieval results cached in the file are cached periodically, they do not necessarily represent the most up to date data.
(2) The retrieval results cached in the file are the results of periodic retrieving of the database, so even data which do not require re-retrieving (data which have not been added to, or updated) are retrieved, resulting in wasted retrieval processing.
(3) Because retrieval results cached in the file are returned to the client, it is not possible to check the client access authorization set for each data to be retrieved.
SUMMARY OF THE INVENTION
The present invention takes into consideration the above problems with an object of improving the data caching method, and providing a client/server distributed system with improved system response speed.
Furthermore, another object of the present invention is to distribute media recorded with the data caching program of the present invention, so that people who acquire the medium can easily establish a data caching apparatus.
As a first means to achieve the objects, there is provided a data caching apparatus in a client/server distributed system, comprising a database for storing a predetermined data, a server for administrating the database, a client which communicates with the server and refers to the database, a retention device for retaining a predetermined number of duplicates of the data, a reference request detection device for detecting that a request is made from the client for reference to the database, a caching device which preferentially sends the duplicate of reference request data retained in the retention device back to the client when the reference request detection device detects a request for reference to the database, a data update device which retrieves the database and updates the duplicate data retained in the retention device, and an execution device for executing the data update device in the server background when the reference request detection device detects a request for reference to the database.
With such a construction, when the client sends a request to the server for reference to the database, the duplicate of reference request data retained in the retention device is preferentially returned to the client. That is, in those cases where the reference request data is retained in the retention device, the duplicate data retained in the retention device is returned to the client. On the other hand, in those cases where the reference request data is not retained in the retention device, the database is retrieved, and the results of the retrieval then sent back to the client. Consequently, provided the reference request data is retained in the retention device, no retrieving of the database occurs, allowing a great improvement in the response speed of the system.
When the client sends a request to the server for reference to the database, the duplicate data retained in the retention device is updated in the server background. That is, the updating of the data retained in the retention device occurs appropriately and it is therefore possible to refer to the most recent data. Furthermore, because the updating of the data retained in the retention device occurs only in the background when the server has surplus processing capability, it does not lower the response speed of the system.
Furthermore, the construction may incorporate an update judgment device for judging whether or not there has been updating of the data stored in the database, between the previous reference request and the current reference request, wherein the execution device executes the data update device in the server background only when the reference request detection device detects a request for reference to the database and the update judgment device judges that there has been updating of the data.
With such a construction, updating of the duplicate data retained in the retention device occurs only when there is a database reference request from the client and when there has been updating of the data retained in the database, between the previous reference request and the current reference request. Consequently, the updating of the duplicate data stored in the retention device is kept to a minimum, and unnecessary retrieving of the database is prevented, so that the system load accompanied with database retrieval processing can be reduced.
Moreover the construction may be such that the database stores access authorization information for the client for each data stored in the database is stored in the database, and there is provided an access authorization judgment device which, when the reference request detection device detects a request for reference to the database, judges whether or not the client has access authorization for the data specified by the reference request, based on the access authorization information stored in the database.
With such a construction, when the client sends a request to the server for reference to the database, a judgment is made as to whether or not the client has access authorization for the reference request data. Consequently, even in those cases where duplicate data retained in the retention device is returned to the client, a check on the access authorization of the client is still conducted, and so the security of the system can be guaranteed.
Furthermore,
Ikuta Masanao
Kambe Tomoaki
Takida Satoshi
Alam Hosain T.
Fujitsu Limited
Shah Sanjiv
Staas & Halsey , LLP
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