System and methods for optimized access in a multi-user environment

• US 5,493,728 A
• Filed: 07/23/1993
• Issued: 02/20/1996
• Est. Priority Date: 02/19/1993
• Status: Expired due to Term

• Current Assignee: Borland Software Corporation (Open Text Corporation)
• Original Assignee: Borland International, Inc. (Open Text Corporation)
• Inventors: Kiuchi, Raymond S., Solton, Randolph T.
• Primary Examiner(s): Treat, William M.
• Assistant Examiner(s): Maung, Zarni
• Application Number:
  US08/096,796
• Time in Patent Office: 942 Days
• Field of Search: 395/600, 395/425, 395/400, 395/250, 364/246.91
• US Class Current: 711/113
• CPC Class Codes: G06F 16/24552 Database cache management
• CPC Class Codes: G09G 5/393 Arrangements for updating the contents of the bit-mapped memory

Abstract

A system of the present invention includes a server connected to one or more workstations or "clients" through a computer network. Methods are provided whereby network data access operations, such as are common in shared data processing, are minimized to only those which are necessary for system operation. In all other instances (i.e., time periods when updating is not needed), a workstation may gain access to the data from a local copy stored in a local buffer, preferably a rapid-access memory of the client. At periodic intervals, a workstation is interrupted for marking its local copy of the data as "invalid"--that is, the copy may be inconsistent with a corresponding version stored on the server. With the next access to the data, the local copy is updated from the version resident on the server. Additional optimization may be added for determining whether the server version has been "touched" (i.e., changed) since last transferred to the local buffer, with the local copy being updated only when such a change has been detected. By maintaining data locally, the penalty incurred with frequent, large data transfers across a network connection is avoided.

Claims

1. In a system comprising a computer network having at least one workstation (client) with a processor and a memory, and said computer network including a server for storing information which may be shared by said at least one workstation, a method for providing access to information stored on said server, said method comprising:

(a) said at least one workstation allocating a buffer in said memory for storing information of interest;

(b) said at least one workstation setting a flag for indicating that information stored in said buffer is invalid;

(c) at a preselected time interval, repeating step (b) for invalidating said buffer by setting said flag, wherein said flag indicates that information in said buffer is invalid at each preselected time interval;

(d) receiving a request for access to said information of interest;

(e) if said flag is set, said computer network transferring information of interest from said server into said memory of said at least one workstation before accessing said information of interest from said buffer; and

(f) said at least one workstation resetting said flag for indicating that information stored in said buffer is valid.

2. The method of claim 1, further comprising:

repeating steps (d)-(f) for a plurality of different requests for information, wherein each request is satisfied by said buffer if said flag is reset.

3. The method of claim 1, wherein said time interval is selected to be sufficiently small so that step (b) is performed at a rate no greater than necessary for processing said information by said at least one workstation.

4. The method of claim 3, wherein said time interval is substantially equal to about 2 seconds.

5. The method of claim 1, wherein said information of interest includes database records stored on said server.

6. The method of claim 1, wherein in step (b) said buffer is only updated if a copy of said information stored in said buffer is not identical to said information stored on said server.

7. The method of claim 1, wherein in step (c) includes the substeps:

setting a system interrupt to occur at a preselected time interval; and

upon occurrence of said interrupt, setting a flag for indicating that information stored in said buffer is invalid.

8. The method of claim 1, wherein in step (c) includes the substeps:

generating a system timer message at a preselected time interval; and

upon receipt of said message, setting a flag for indicating that information stored in said buffer is invalid, wherein said time interval is adjusted to compensate for any differences between generation of said system timer message (actual time) and receipt of said system timer message (apparent time).

9. A server-base networking system with improved data access comprising:

a server having a storage device;

at least one client operably coupled to said server through a communication line, each said at least one client having a processor and a memory;

time-based means for setting a flag to indicate a copy of data in said memory of said at least one client as invalid at a periodic time interval, said copy of data being from said storage device of said server and indicated as invalid by said flag at each periodic time interval; and

means, responsive to a request for data marked as invalid, for transferring a valid copy of data from said storage device of said server to said memory of said at least one client.

10. The system of claim 9, wherein said processor is an Intel®

80×

86 class microprocessor and wherein said time-based means includes a real-time clock (RTC) capable of generating preemptive interrupts.

11. The system of claim 9, wherein said time interval is empirically selected to optimized data access.

12. The system of claim 9, wherein said time interval is selected from a range of about 1 to 4 seconds.

13. The system of claim 9, wherein said time interval substantially equals about 2 seconds.

14. In a data processing system having first and second storage means, said second storage means storing data and having a slower data access time than that of said first storage means, a method for concurrently accessing data, the method comprising:

(a) said system transferring a copy of said data from said second storage means to said first storage means, wherein a valid copy of said data is maintained in said first storage means;

(b) after a time interval, said system resetting a flag to indicate said copy as invalid, wherein said flag indicates said copy is invalid at each time interval;

(c) said system receiving a request for access to said data; and

(d) said system repeating step (a) if said copy is marked as invalid.

15. The method of claim 14, wherein said flag is set when a copy of said data is transferred to said first storage means and reset at said time interval.

16. The method of claim 14, further comprising:

only transferring a new copy to said first storage means when said data resident on said second storage means has been modified.

17. The method of claim 14, wherein said data includes at least one database record.

18. The method of claim 14, wherein said time interval is about 1 to 4 seconds.

19. The method of claim 14, wherein said time interval is about 2 seconds.

20. An information storage and retrieval system comprising:

first storage means including a volatile memory;

second storage means including a non-volatile memory for storing data objects;

means for setting a status flag to indicate a copy of a data object resident in said first storage means at a preselected time interval, said flag indicating said copy is invalid at each preselected time interval; and

means, responsive to a request for access to said data object, for transferring a new copy of said data object from said second storage means to said first storage means when said copy is invalid.

21. The system of claim 20, wherein said first storage means includes a random-access memory (RAM).

22. The system of claim 20, wherein said second storage means includes a storage disk.

23. The system of claim 20, further comprising:

real-time clock means for generating a signal at said preselected time interval, said setting means being responsive to said signal.