System and method for decoupling object identification for the purpose of object switching in database systems

• US 20040220940A1
• Filed: 04/29/2003
• Published: 11/04/2004
• Est. Priority Date: 03/14/2003
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Huras, Matthew Albert, Sachedina, Aamer, Romanufa, Keriley K., Flasza, Miroslaw Adam, Winer, Michael Jeffrey, Berks, Robert T., Lau, Leo Tat Man
• Granted Patent: US 7,099,889 B2
• Time in Patent Office: Days
• US Class Current: 707/100
• CPC Class Codes: G06F 16/20 of structured data, e.g. relational data
• CPC Class Codes: Y10S 707/955 Object-oriented
• CPC Class Codes: Y10S 707/99938 Concurrency, e.g. lock management in shared database
• CPC Class Codes: Y10S 707/99942 Manipulating data structure, e.g. compression, compaction, compilation
• CPC Class Codes: Y10S 707/99944 Object-oriented database structure
• CPC Class Codes: Y10S 707/99953 Recoverability

Abstract

The use of a centralized version table allows for efficient object switching. Rather than synchronizing all database agents to recognize a newly created file as containing the most recent version of a given object, database agents requiring access to the given object need only consult the centralized version table to learn file identity information. That is, the database agents consult the centralized version table to determine which of the files associated with a given object contain the most recent version of the given object. Mechanisms associated with the use of the centralized version table also provide for efficient recovery from a failure that has occurred during an object switching transaction.

Claims

1. A management method for switching a database object in a database that stores a plurality of database objects, wherein multiple versions of database objects are stored in a plurality of files, each of the plurality of files being identified by a file handle, the method, comprising:

locating an indication of a version of a file handle that is related to an object handle that identifies an object stored in the database;

preventing database agents from accessing the indication of the version; and

changing the indication of the version to a value that refers to a second file handle.

2. The method of claim 1, further comprising providing a version tuple for associating the indication of the version with the object handle for the database object.

3. The method of claim 2, wherein the version tuple is stored in a centralized version table;

and

wherein locating the indication of the version comprises searching the centralized version table for the version tuple.

4. The method of claim 3, further comprising determining whether the version tuple exists in the centralized version table;

and

creating a new version tuple that includes the object handle.

5. The method of claim 3, wherein preventing the database agents from accessing the indication of the version comprises acquiring an exclusive lock on the version tuple.

6. The method of claim 5, wherein acquiring the exclusive lock on the version tuple comprises:

waiting for existing input and output operations against the database object to finish; and

preventing new input and output operations against the database object from starting.

7. The method of claim 5, further comprising releasing the exclusive lock on the version tuple so that new input and output operations against the database object is performed by the database agents.

8. The method of claim 1, wherein the indication of the version is binary;

and

wherein changing the indication of the version comprises toggling the value of the indication of the version.

9. The method of claim 1, further comprising distinguishing between a file that stores a shadow version of the database object and a file that stores a current version of the database object.

10. The method of claim 9, further comprising updating a lookup table to reflect which file stores the shadow version of the database object and which file stores a current version of the database object.

11. A management computer program product having instruction codes for switching a database object in a database that stores a plurality of database objects, wherein multiple versions of database objects are stored in a plurality of files, each of the plurality of files being identified by a file handle, the computer program product, comprising:

a first set of instruction codes for locating an indication of a version of a file handle that is related to an object handle that identifies an object stored in the database;

a second set of instruction codes for preventing database agents from accessing the indication of the version; and

a third set of instruction codes for changing the indication of the version to a value that refers to a second file handle.

12. The computer program product of claim 11, further comprising a fourth set of instruction codes for providing a version tuple for associating the indication of the version with the object handle for the database object.

13. The computer program product of claim 12, wherein the version tuple is stored in a centralized version table;

and

wherein the first set of instruction codes searches the centralized version table for the version tuple.

14. The computer program product of claim 13, further comprising a fifth set of instruction codes for determining whether the version tuple exists in the centralized version table;

and

a sixth set of instruction codes for creating a new version tuple that includes the object handle.

15. The computer program product of claim 13, wherein the second set of instruction codes acquires an exclusive lock on the version tuple.

16. The computer program product of claim 15, wherein the second set of instruction codes waits for existing input and output operations against the database object to finish;

and

prevents new input and output operations against the database object from starting.

17. The computer program product of claim 15, further comprising a seventh set of instruction codes for releasing the exclusive lock on the version tuple so that new input and output operations against the database object is performed by the database agents.

18. The computer program product of claim 11, wherein the indication of the version is binary;

and

wherein the third set of instruction codes toggles the value of the indication of the version.

19. The computer program product of claim 11, further comprising an eight set of instruction codes for distinguishing between a file that stores a shadow version of the database object and a file that stores a current version of the database object.

20. The computer program product of claim 19, further comprising a ninth set of instruction codes for updating a lookup table to reflect which file stores the shadow version of the database object and which file stores a current version of the database object.

31. A management method for switching a database object in a database that stores a plurality of database objects, wherein multiple versions of database objects are stored in a plurality of files, each of the plurality of files being identified by a file handle, the method comprising:

scanning a tablespace directory for evidence of object shadowing, wherein the evidence of object shadowing comprises an association of at least two files with a given database object among the plurality of database objects;

selecting a database object for which evidence of object shadowing has been found, to provide a selected database object, wherein the selected database object comprises at least two associated files;

attempting to read a sequence information and object marking indications from the at least two associated files; and

determining which of the at least two associated files contains a current version of the selected database object based on the sequence information and object marking indications.

32. The method of claim 31, further comprising, based on the sequence information and the object marking indications:

determining that a failure has occurred during an object switching transaction; and

determining a logical segment of the object switching transaction at which to resume the object switching transaction.

33. A management computer program product having instruction codes for switching a database object in a database that stores a plurality of database objects, wherein multiple versions of database objects are stored in a plurality of files, each of the plurality of files being identified by a file handle, the method comprising:

a first set of instruction codes for scanning a tablespace directory for evidence of object shadowing, wherein the evidence of object shadowing comprises an association of at least two files with a given database object among the plurality of database objects;

a second set of instruction codes for selecting a database object for which evidence of object shadowing has been found, to provide a selected database object, wherein the selected database object comprises at least two associated files;

a third set of instruction codes for attempting to read a sequence information and object marking indications from the at least two associated files; and

a fourth set of instruction codes for determining which of the at least two associated files contains a current version of the selected database object based on the sequence information and object marking indications.

34. The method of claim 33, further comprising, based on the sequence information and the object marking indications:

a fifth set of instruction codes for determining that a failure has occurred during an object switching transaction; and

a sixth set of instruction codes for determining a logical segment of the object switching transaction at which to resume the object switching transaction.

35. A system for switching a database object in a database that stores a plurality of database objects, wherein multiple versions of database objects are stored in a plurality of files, each of the plurality of files being identified by a file handle, the method comprising:

means for scanning a tablespace directory for evidence of object shadowing, wherein the evidence of object shadowing comprises an association of at least two files with a given database object among the plurality of database objects;

means for selecting a database object for which evidence of object shadowing has been found, to provide a selected database object, wherein the selected database object comprises at least two associated files;

means for attempting to read a sequence information and object marking indications from the at least two associated files; and

means for determining which of the at least two associated files contains a current version of the selected database object based on the sequence information and object marking indications.

36. The system of claim 35, further comprising, based on the sequence information and the object marking indications:

a fifth set of instruction codes for determining that a failure has occurred during an object switching transaction; and

a sixth set of instruction codes for determining a logical segment of the object switching transaction at which to resume the object switching transaction.