Method and apparatus providing optimistic locking of shared computer resources

• US 6,850,938 B1
• Filed: 02/08/2001
• Issued: 02/01/2005
• Est. Priority Date: 02/08/2001
• Status: Active Grant

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Inventors: Sadjadi, Shahrokh
• Primary Examiner(s): Alam, Shahid
• Assistant Examiner(s): PHAM, HUNG Q
• Application Number:
  US09/781,525
• Time in Patent Office: 1,454 Days
• Field of Search: 707/8, 707/9, 709/248, 713/165, 713/167, 711/150, 711/151
• US Class Current: 1/1
• CPC Class Codes: G06F 16/2315 Optimistic concurrency control
• CPC Class Codes: G06F 16/2343 Locking methods, e.g. distributed locking or locking implementation details
• CPC Class Codes: Y10S 707/99938 Concurrency, e.g. lock management in shared database
• CPC Class Codes: Y10S 707/99939 Privileged access

Abstract

Techniques for concurrent access to a resource object, such as a database, include generating a lock data structure for a particular resource object. The lock data structure includes data values for a resource object identification, a lock type, and a version number. The version number is related to a number of changes to the resource object since the lock data structure was generated. A request is received from a requesting process. The request is for a requested lock type for access to the particular resource object. It is determined whether to grant the request based on the requested lock type and the lock type in the lock data structure. By carrying a lock version number in a lock data structure managed by a lock manager, improved optimistic locking is provided in a database. In particular, the approach enables introduction of optimistic locking to a legacy database without requiring burdensome changes to a database table schema.

Claims

1. A method of updating a resource object using optimistic locks, the method comprising the computer-implemented steps of:

receiving from a client process a request to update a particular resource object;

sending to a lock manager process a request for a first lock for access to the particular resource object, the request including data indicating an optimistic lock type;

receiving the first lock for access to the particular resource object, the first lock including data indicating the resource object, the optimistic lock type and a first value for a version number related to a number of changes to the resource object since the lock manager generated a lock data structure corresponding to the resource object; and

updating the resource object by

sending to a lock manager process a request for a second lock for access to the particular resource object, the request including data indicating the resource object identification and an exclusive lock type;

receiving the second lock for access to the particular resource object, the second lock including data indicating the resource object identification, the exclusive lock type and a second value for the version number;

determining whether the second value for the version number substantially equals the first value for the version number; and

if the second value substantially equals the first value, then

committing an updated resource object to the resource, and

replacing the second value for the version number in the second lock with a third value for the version number, the third value computed by adding the second value and a predetermined version change value.

2. A method as recited in claim 1, wherein:

the second lock further comprises a reference number set to a predetermined initial value,

the method further comprising the steps of;

receiving the second lock to be released having data indicating the particular resource object;

determining whether the reference number of the second lock to be released substantially equals the predetermined initial value of the reference number; and

if it is determined the reference number of the second lock to be released does not substantially equal the predetermined initial value, then replacing the value of the reference number in the second lock with a difference substantially equal to the value of the reference number in the second lock minus a predetermined reference change value.

3. A method as recited in claim 2, further comprising, if it is determined the reference number of the second lock to be released substantially equals the predetermined initial value, then deleting the second lock for the particular resource object.

4. The method as recited in claim 1, further comprising, if the second value does not substantially equal the first value, then sending a message to the client process, the message indicating that the resource object was not updated.

5. The method as recited in claim 4, further comprising sending to the lock manager process a release message to release the second lock, the release message including data indicating the third value of the version number in the second lock and the exclusive lock type, wherein the third value of the version nwnber is used by the lock manager to replace the second value of the version number in the lock data structure.

6. The method as recited in claim 1, further comprising sending to the lock manager process a first release message to release the first lock.

7. The method as recited in claim 6, further comprising sending to the lock manager process a second release message to release the second lock.

8. A computer-readable medium carrying one or more sequences of instructions for updating a resource object, which instructions, when executed by one or more processors, cause the one or more processors to carry out the steps of:

receiving from a client process a request to update a particular resource object;

sending to a lock manager process a request for a first lock for access to the particular resource object, the request including data indicating an optimistic lock type;

receiving the first lock for access to the particular resource object, the first lock including data indicating the resource object, the optimistic lock type and a first value for a version number related to a number of changes to the resource object since the lock manager generated a lock data structure corresponding to the resource object; and

updating the resource object by

sending to a lock manager process a request for a second lock for access to the particular resource object, the request including data indicating the resource object identification and an exclusive lock type;

receiving the second lock for access to the particular resource object, the second lock including data indicating the resource object identification, the exclusive lock type and a second value for the version number;

determining whether the second value for the version number substantially equals the first value for the version number, and

if the second value substantially equals the first value, then

committing an updated resource object to the resource, and

replacing the second value for the version number in the second lock with a third value for the version number, the third value computed by adding the second value and a predetermined version change value.

9. The computer-readable medium as recited in claim 8, wherein the instructions, when executed by one or more processors, cause the one or more processors to carry out the step of:

if the second value does not substantially equal the first value, then sending a message to the client process, the message indicating that the resource object was not updated.

10. The computer-readable medium as recited in claim 9, wherein the instructions, when executed by one or more processors, cause the one or more processors to carry out the step of:

sending to the lock manager process a release message to release the second lock, the release message including data indicating the third value of the version number in the second lock and the exclusive lock type, wherein the third value of the version number is used by the lock manager to replace the second value of the version number in the lock data structure.

11. The computer-readable medium as recited in claim 8, wherein the instructions, when executed by one or more processors, cause the one or more processors to carry out the step of:

sending to the lock manager process a first release message to release the first lock.

12. The computer-readable medium as recited in claim 11, wherein the instructions, when executed by one or more processors, cause the one or more processors to carry out the step of:

sending to the lock manager process a second release message to release the second lock.

13. The computer-readable medium of claim 8, wherein the second lock further comprises a reference number set to a predetermined initial value, and wherein the instructions cause the one or more processors to perform the steps of:

receiving the second lock to be released having data indicating the particular resource object;

determining whether the reference number of the second lock to be released substantially equals the predetermined initial value of the reference number; and

if it is determined the reference number of the second lock to be released does not substantially equal the predetermined initial value, then replacing the value of the reference number in the second lock with a difference substantially equal to the value of the reference number in the second lock minus a predetermined reference change value.

14. A computer-readable medium of claim 13, wherein the instructions cause the one or more processors to perform the step of, if it is determined the reference number of the second lock to be released substantially equals the predetermined initial value, then deleting the second lock for the particular resource object.

15. An apparatus for updating a resource object, comprising:

a processor;

one or more stored sequences of instructions which, when executed by the processor, cause the processor to carry out the steps of;

receiving from a client process a request to update a particular resource object;

sending to a lock manager process a request for a first lock for access to the particular resource object, the request including data indicating an optimistic lock type,

receiving the first lock for access to the particular resource object, the first lock including data indicating the resource object, the optimistic lock type and a first value for a version number related to a number of changes to the resource object since the lock manager generated a lock data structure corresponding to the resource object; and

updating the resource object by

sending to a lock manager process a request for a second lock for access to the particular resource object, the request including data indicating the resource object identification and an exclusive lock type;

receiving the second lock for access to the particular resource object, the second lock including data indicating the resource object identification, the exclusive lock type and a second value for the version number,

determining whether the second value for the version number substantially equals the first value for the version number, and

if the second value substantially equals the first value, then

committing an updated resource object to the resource, and

replacing the second value for the version number in the second lock with a third value for the version number, the third value computed by adding the second value and a predetermined version change value.

16. The apparatus as recited in claim 15, wherein the instructions, when executed by one or more processors, cause the one or more processors to carry out the step of:

the second value does not substantially equal the first value, then sending a message to the client process, the message indicating that the resource object was not updated.

17. The apparatus as recited in claim 16, wherein the instructions, when executed by one or more processors, cause the one or more processors to carry out the step of:

sending to the lock manager process a release message to release the second lock, the release message including data indicating the third value of the version number in the second lock and the exclusive lock type, wherein the third value of the version number is used by the lock manager to replace the second value of the version number in the lock data structure.

18. The apparatus as recited in claim 15, wherein the instructions, when executed by one or more processors, cause the one or more processors to carry out the step of:

sending to the lock manager process a first release message to release the first lock.

19. The apparatus as recited in claim 18, wherein the instructions, when executed by one or more processors, cause the one or more processors to carry out the step of:

sending to the lock manager process a second release message to release the second lock.

20. The apparatus of claim 15, wherein the second lock further comprises a reference number set to a predetermined initial value, and wherein the instructions cause the one or more processors to perform the steps of:

receiving the second lock to be released having data indicating the particular resource object;

determining whether the reference number of the second lock to be released substantially equals the predetermined initial value of the reference number; and

if it is determined the reference number of the second lock to be released does not substantially equal the predetermined initial value, then replacing the value of the reference number in the second lock with a difference substantially equal to the value of the reference number in the second lock minus a predetermined reference change value.

21. The apparatus of claim 20, wherein the instructions cause the one or more processors to perform the steps of:

if it is determined the reference number of the second lock to be released substantially equals the predetermined initial value, then deleting the second lock for the particular resource object.

22. An apparatus for updating a resource object, comprising:

a means for receiving from a client process a request to update a particular resource object;

a means for sending to a lock manager process a request for a first lock for access to the particular resource object, the request including data indicating an optimistic lock type;

a means for receiving the first lock for access to the particular resource object, the first lock including data indicating the resource object, the optimistic lock type and a first value for a version number related to a number of changes to the resource object since the lock manager generated a lock data structure corresponding to the resource object; and

a means for updating the resource object, including

a means for sending to a lock manager process a request for a second lock for access to the particular resource object, the request including data indicating the resource object identification and an exclusive lock type;

a means for receiving the second lock for access to the particular resource object, the second lock including data indicating the resource object identification, the exclusive lock type and a second value for the version number;

a means for determining whether the second value for the version number substantially equals the first value for the version number;

a means for committing an updated resource object to the resource if the second value substantially equals the first value; and

a means for replacing the second value for the version number in the second lock with a third value for the version number if the second value substantially equals the first value, the third value computed by adding the second value and a predetermined version change value.

23. The apparatus as recited in claim 22, further comprising:

means for sending a message to the client process if the second value does not substantially equal the first value, the message indicating that the resource object was not updated.

24. The apparatus as recited in claim 23, further comprising:

means for sending to the lock manager process a second release message to release the second lock, the second release message including data indicating the third value of the version number in the second lock and the exclusive lock type, wherein the third value of the version number is used by the lock manager to replace the second value of the version number in the lock data structure.

25. The apparatus as recited in claim 22, further comprising:

means for sending to the lock manager process a fist release message to release the first lock.

26. The apparatus as recited in claim 25, further comprising:

means for sending to the lock manager process a second release message to release the second lock.

27. The apparatus of claim 22, wherein the second lock further comprises a reference number set to a predetermined initial value, the apparatus further comprising:

means for receiving the second lock to be released having data indicating the particular resource object;

means for determining whether the reference number of the second lock to be released substantially equals the predetermined initial value of the reference number; and

means for replacing the value of the reference number in the second lock with a difference substantially equal to the value of the reference number in the second lock minus a predetermined reference change value, if it is determined the reference number of the second lock to be released does not substantially equal the predetermined initial value.

28. The apparatus of claim 27, further comprising:

means for deleting the second lock for the particular resource object if it is determined the reference number of the second lock to be released substantially equals the predetermined initial value.