Data processing: database and file management or data structures – Database design – Data structure types
Reexamination Certificate
1998-03-27
2001-04-03
Black, Thomas (Department: 2771)
Data processing: database and file management or data structures
Database design
Data structure types
C707S793000, C707S793000, C707S793000, C707S793000
Reexamination Certificate
active
06212520
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a database management system based on the client/server architecture, and more particularly to a database management system of this kind constructed such that machines for sending a request for processing to a database are different from the machine that actually executes the requested processing.
2. Description of the Related Art
Conventionally, in the database management system based on the client/server architecture, the server software operates on a server machine to execute processing of the database, while the client software operates on a client machine on a network to which the server machine is connected. The network conveys requests for processing to the server and the results of the requests to the client.
In using a database managed by the database management system operating on a network to which the client machines and the server machine are connected, in general, when the client makes a request for access to the database, the server creates an executing entity which executes the request from the client and sends back the results of the processing of the request to the client. When the processing of the request is terminated, the executing entity is terminated or deleted. When the executing entity is created, resources of the server are allocated to the executing entity, and when the executing entity is terminated, the resources allocated to the executing entity are relinquished as well. These resources include memory in the server machine, a transaction lock controlled by the database management system for exclusive control, a memory area in a secondary storage medium for carrying out sorting operations, etc.
The machines based on the client-server architecture exist in operating environments different from each other. These machines use, as their operating systems, Windows 95 and Windows NT (Windows 95 and Windows NT are registered trademarks of Microsoft Corporation in the United States and other countries), or UNIX (developed and licensed by UNIX System Laboratories) -based operating systems. In the described configuration, during communications between a client machine and the server machine, the client machine may crash or the power thereof may be unexpectedly turned off. When one of these situations occurs after a request for access to the database is sent from the client machine to the server machine, information on the down conditions of the client machine is not sent to the server machine. The result is that the server carries out the processing in response to the request for access to the database, but the machine to which the results should be returned is no longer connected to the network so that the executing entity started in response to the request for access to the database continues to run and the resources allocated thereto remain unavailable on the server machine. As a result, when another client sends a request for access to the database to the server machine, there can be a case in which there are no resources which can be allocated to an executing entity newly created in response to the request, so that this client may be compelled to wait. Further, the client machine can go down not only when the power is turned off, but also when the reset button of the client machine is depressed.
To eliminate the inefficiency of the resources remaining allocated to an executing entity created for a client machine that made a request for access to the database but that went down thereafter, two methods are typically employed:
FIG. 5
is a block diagram schematically showing the arrangement of a conventional database management system. In
FIG. 5
, a client machine
101
and a server machine
111
are connected to a network
120
, and the network
120
has an operator terminal
130
connected thereto and used in server administration. It is now assumed that in the client machine
101
, a client process
102
has been started, while a database management system (DBMS) server process
112
has been started in the server machine
111
. The database management system server process
112
has created a database (DB) access executing entity
113
in response to a request for access to the database from the client process
102
, and resources
114
have been allocated to the database access executing entity
113
. Further, the server machine
111
has a recovery command
115
provided therein for terminating the executing entity.
When the operator of the server monitors requests from the client, and if he recognizes that the power of the client machine
101
on which the client process
102
operates is in the OFF state due to some unknown cause during the access of the client process
102
to the database, he executes the recovery command
115
on the server machine via the operator terminal
130
. The recovery command
115
terminates the database access executing entity
113
created in response to the request for access to the database from the client process
102
and relinquishes the resources
114
allocated to the database access executing entity
113
for the processing of the request. This makes these resources on the server machine
111
available for another client which makes a request for access to the database.
FIG. 6
is a block diagram schematically showing another example of construction of a conventional database management system. In
FIG. 6
, a client machine
101
and a server machine
141
are connected to a network
120
. In the server machine
141
, a database management system server process
142
operating thereon includes a database (DB) access executing entity
143
, resources
144
, and an executing entity control daemon
145
for controlling the database (DB) access executing entity
143
. Further, the server machine
141
is capable of executing a network-monitoring function
146
provided by its operating system (OS).
When the client process
102
on the client machine
101
communicates with the database management system server process
142
on the server machine
141
, both the machines are required to designate a port for sending and receiving messages between the two machines. In general, the combination of a port on one client machine
101
and a port on the server machine
141
, combined with a physical medium for carrying out serial transfer of messages between the machines, is hereinafter called “a communication path”. In one combination of one port of the client machine and one port of the server machine, there can exist a number of communication paths each of which can send and receive messages in parallel with another. “Socket” is one typical example of a communication path. Details of the “Socket” are described in literature “UNIX NETWORK PROCESSING,” W. Richard Stevens, 1990 by Prentice Hall, Inc. A Simon & Schuster Company Englewood Cliffs, N.J. 07632.
Now, in order to make use of the network function of the operating system, the port via which communications are carried out is registered with the operating system. The network-monitoring function
146
of the operating system checks for a time during which communications are not being carried out, for each communication path, and if the communication path is not used for a predetermined time period, the communication path is canceled, and the process waiting to receive data via the communication path is notified of the cancellation of the communication path. The time period with reference to which the cancellation of each communication path is determined is set by the system administrator. When the executing entity control daemon
145
of the database management system server process
142
is notified of the cancellation of the communication path from its communications environment, it terminates the database access executing entity
143
which has been communicating via the communication path and keeping the resources
144
unavailable to other executing entities.
Thus, in the database management system which makes use of the clock function of the operating system for the netwo
Maruyama Hidefumi
Nakamura Hiroyuki
Takahashi Kouji
Black Thomas
Do Thuy
Fujitsu Limited
Staas & Halsey , LLP
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