Techniques for maintaining consistency for different requestors of files in a database management system

• US 7,548,918 B2
• Filed: 12/16/2004
• Issued: 06/16/2009
• Est. Priority Date: 12/16/2004
• Status: Active Grant

• Current Assignee: Oracle International Corporation (Oracle Corporation)
• Original Assignee: Oracle International Corporation (Oracle Corporation)
• Inventors: Sedlar, Eric, Jain, Namit, Idicula, Sam, Murthy, Ravi, Agarwal, Nipun, Pannala, Syam
• Primary Examiner(s): Mofiz; Apu M
• Assistant Examiner(s): Le; Hung D
• Application Number:
  US11/013,890
• Publication Number:
  US 20060136516A1
• Time in Patent Office: 1,643 Days
• Field of Search: None
• US Class Current: 1/1
• CPC Class Codes: G06F 16/1774 Locking methods, e.g. locking methods for file systems allowing shared and concurrent access to files
• CPC Class Codes: Y10S 707/99938 Concurrency, e.g. lock management in shared database
• CPC Class Codes: Y10S 707/99939 Privileged access

Abstract

A method and apparatus for providing file system operation locks at a database server is provided. A database server may employ database locks and file system operation locks in servicing requests from consistent requestors and inconsistent requesters. A database lock is a lock that is obtained in response to performing a database operation, and the database lock is released when the database operation has successfully completed. A file system operation lock is a lock that is obtained in response to performing an OPEN file system operation, and the file system operation lock is released when a CLOSE file system operation is performed. The database server may use a temporary copy of the resource, which reflects all the current changes that have been made to the resource by database operations, in servicing consistent requestors, and may use the original version of the resource in servicing inconsistent requesters.

Claims

1. A machine-implemented method, comprising:

receiving a request to perform a file system operation, wherein performance of said file system operation requires performance of a plurality of database operations involving one or more resources;

performing said file system operation,

wherein performing said file system operation comprises the steps of;

obtaining a first set of locks that apply to said one or more resources, wherein each lock in said first set of locks is a first type of lock;

wherein the first type of lock is a file-based lock;

performing said plurality of database operations in a plurality of database transactions;

for each database transaction of said plurality of transactions, obtaining a second set of locks on the resources, of said one or more resources, that are involved in database operations that are performed during said database transaction, wherein each lock in said second set of locks is a second type of lock;

wherein the second type of lock is database lock;

releasing locks of said second type of lock in response to successful completion of the corresponding database transaction;

wherein releasing locks of said second type includes releasing a lock on a particular resource involved in a particular database transaction upon successful completion of the database transaction prior to successful completion of said file system operation; and

releasing locks of said first type of lock in response to successful completion of said file system operation.

2. The method of claim 1, further comprising:

receiving, from a requestor, a request for a particular resource of said one or more resources;

determining which version of the particular resource to provide to the requestor based on (a) the requestor type of the requestor and (b) which types of locks are currently held on the particular resource.

3. The method of claim 2 wherein:

a lock of the first type is held on the particular resource;

no lock of the second type is held on the particular resource;

if the requestor is a first type of requestor, then the requestor is provided a current version of the particular resource; and

if the requestor is a second type of requestor, then the requestor is provided a version of the particular resource that does not reflect any changes that were made since the lock of the first type was granted on the particular resource.

4. The method of claim 3 wherein:

if the request is in the form of a database command, then the requestor qualifies as the first type of requestor; and

if the request is in the form of a file system operation request, then the requestor qualifies as the second type of requestor.

5. The method of claim 2, wherein said step of determining which version of the particular resource to provide to the requestor comprises the step of:

determining whether said requestor is receive an older version of said particular resource or a newer version of said particular resource based on said requestor type.

6. The method of claim 2, wherein said step of determining which version of the particular resource to provide to the requestor comprises the step of:

determining said requestor type based, at least in part, on the type of protocol associated with said second request.

7. The method of claim 1, further comprising the steps of:

prior to performing any database operation that changes a particular resource of said one or more resources, storing a temporary copy of said particular resource; and

making changes to said particular resource by making changes to said temporary copy, as long as a particular lock, of said first set of locks, is held on said particular resource.

8. The method of claim 1, further comprising the steps of:

prior to performing a database operation, in said plurality of database operations, that changes a particular resource of said one or more resources, storing a snapshot time in association with said particular resource, wherein the snapshot time indicates a logical time prior to the performance of said database operation; and

reconstructing a version of the particular resource prior to the performance of said plurality of database operations using said snapshot time.

9. The method of claim 8, further comprising the step of:

providing said reconstructed version of the particular resource to a file system client.

10. The method of claim 1, wherein said step of performing said plurality of database operations comprises the steps of:

making a first copy of a particular resource, of said one or more resources, based on an original version of said particular resource;

establishing said first copy as the current version of said particular resource;

making said change to said first copy; and

committing said change to said first copy.

11. The method of claim 10, wherein said first copy is a constructed version of said resource, and wherein said original version of said resource is a deconstructed version of said resource.

12. The method of claim 11, wherein the step of making said first copy comprises the steps of:

constructing said constructed version of said resource based on said deconstructed version of said particular resource; and

storing said constructed version of said particular resource in a particular column of a database table.

13. The method of claim 10, wherein:

the particular resource is stored in a database,

said step of copying said original version of said particular resource to said first copy comprises storing said first copy in a LOB column in a row of a database table within said database, and

said row is associated with said original version of said particular resource.

14. The method of claim 1, wherein said step of performing said plurality of database operations comprises the following steps:

if certain criteria are satisfied, then

making a copy of a particular resource,

establishing the copy as the current version of the particular resource, and

committing the change to the copy;

if said certain criteria are not satisfied, then

storing a snapshot time that reflects a particular point in time wherein the change is committed to the copy, and

committing the change to the current version of the particular resource without making a copy of the current version of the resource.

15. The method of claim 14 wherein the certain criteria is based on whether undo information associated with said change will be retained for a particular amount of time.

16. The method of claim 1, wherein said step of performing said plurality of database operations comprises the steps of:

storing a snapshot time with a particular resource of said one or more resources, wherein said snapshot time indicates a logical time prior to when a change is committed to said particular resource;

making said change to said particular resource.

17. The method of claim 16, further comprising the step of:

reconstructing said particular resource to reflect a state identified by said snapshot time using undo information.

18. A computer-readable storage medium carrying one or more sequences of instructions which, when executed by one or more processors, causes the one or more processors to perform the steps of:

receiving a request to perform a file system operation, wherein performance of said file system operation requires performance of a plurality of database operations involving one or more resources;

performing said file system operation,

wherein performing said file system operation comprises the steps of;

obtaining a first set of locks that apply to said one or more resources, wherein each lock in said first set of locks is a first type of lock;

wherein the first type of lock is a file-based lock;

performing said plurality of database operations in a plurality of database transactions;

for each database transaction of said plurality of transactions, obtaining a second set of locks on the resources, of said one or more resources, that are involved in database operations that are performed during said database transaction, wherein each lock in said second set of locks is a second type of lock;

wherein the second type of lock is database lock;

releasing locks of said second type of lock in response to successful completion of the corresponding database transaction;

wherein releasing locks of said second type includes releasing a lock on a particular resource involved in a particular database transaction upon successful completion of the database transaction prior to successful completion of said file system operation; and

releasing locks of said first type of lock in response to successful completion of said file system operation.

19. The computer-readable storage medium of claim 18 further carrying one or more sequences of instructions which, when executed by one or more processors, causes the one or more processors to perform the steps of:

receiving, from a requestor, a request for a particular resource of said one or more resources;

determining which version of the particular resource to provide to the requestor based on (a) the requestor type of the requestor and (b) which types of locks are currently held on the particular resource.

20. The computer-readable storage medium of claim 19 wherein;

a lock of the first type is held on the particular resource;

no lock of the second type is held on the particular resource;

if the requestor is a first type of requestor, then the requestor is provided a current version of the particular resource; and

if the requestor is a second type of requestor, then the requestor is provided a version of the particular resource that does not reflect any changes that were made since the lock of the first type was granted on the particular resource.

21. The computer-readable storage medium of claim 20 wherein,

if the request is in the form of a database command, then the requestor qualifies as the first type of requestor;

and

if the request is in the form of a file system operation request, then the requestor qualifies as the second type of requestor.

22. The computer-readable storage medium of claim 19 wherein said step of determining which version of the particular resource to provide to the requestor comprises the step of:

determining whether said requestor is to receive an older version of said particular resource or a newer version of said particular resource based on said requestor type.

23. The computer-readable storage medium of claim 19 wherein said step of determining which version of the particular resource to provide to the requestor comprises the step of:

determining said requestor type based, at least in part, on the type of protocol associated with said second request.

24. The computer-readable storage medium of claim 18 further carrying one or more sequences of instructions which, when executed by one or more processors, causes the one or more processors to perform the step of:

prior to performing any database operation that changes a particular resource of said one or more resources, storing a temporary copy of said particular resource; and

making changes to said particular resource by making changes to said temporary copy, as long as a particular lock, of said first set of locks, is held on said particular resource.

25. The computer-readable storage medium of claim 18 further carrying one or more sequences of instructions which, when executed by one or more processors, causes the one or more processors to perform the steps of:

prior to performing a database operation, in said plurality of database operations, that changes a particular resource of said one or more resources, storing a snapshot time in association with said particular resource, wherein the snapshot time indicates a logical time prior to the performance of said database operation; and

reconstructing a version of the particular resource prior to the performance of said plurality of database operations using said snapshot time.

26. The computer-readable storage medium of claim 25 further carrying one or more sequences of instructions which, when executed by one or more processors, causes the one or more processors to perform the step of:

providing said reconstructed version of the particular resource to a file system client.

27. The computer-readable storage medium of claim 18, wherein said step of performing said plurality of database operations comprises the steps of:

making a first copy of a particular resource, of said one or more resources, based on an original version of said particular resource;

establishing said first copy as the current version of said particular resource;

making said change to said first copy; and

committing said change to said first copy.

28. The computer-readable storage medium of claim 27 wherein said first copy is a constructed version of said resource, and wherein said original version of said resource is a deconstructed version of said source.

29. The computer-readable storage medium of claim 28 wherein the step of making said first copy comprises the step of:

constructing said constructed version of said resource based on said deconstructed version of said particular resource; and

storing said constructed version of said particular resource in a particular column of a database table.

30. The computer-readable storage medium of claim 27 wherein:

the particular resource is stored in a database,

said step of copying said original version of said particular resource to said first copy comprises storing said first copy in a LOB column in a row of a database table within said database, and

said row is associated with said original version of said particular resource.

31. The computer-readable storage medium of claim 18 wherein said step of performing said plurality of database operations comprises the following steps:

if certain criteria are satisfied, then

making a copy of a particular resource, establishing the copy as the current version of the particular resource, and committing the change to the copy;

if said certain criteria are not satisfied, then

storing a snapshot time that reflects a particular point in time wherein the change is committed to the copy, and committing the change to the current version of the particular resource without making a copy of the current version of the resource.

32. The computer-readable storage medium of claim 31 wherein the certain criteria is based on whether undo information associated with said change will be retained for a particular amount of time.

33. The computer-readable storage medium of claim 18 wherein said step of performing said plurality of database operations comprises the steps of:

storing a snapshot time with a particular resource of said one or more resources, wherein said snapshot time indicates a logical time prior to when a change is committed to said particular resource;

making said change to said particular resource.

34. The computer-readable storage medium of claim 33 further carrying one or more sequences of instructions which, when executed by one or more processors, causes the one or more processors to perform the step of:

reconstructing said particular resource to reflect a state identified by said snapshot time using undo information.