System and method for retrieving information from a database

• US 7,203,691 B2
• Filed: 09/27/2002
• Issued: 04/10/2007
• Est. Priority Date: 09/27/2002
• Status: Active Grant

• Current Assignee: Teradata US, Inc. (Teradata Corporation)
• Original Assignee: NCR Corporation
• Inventors: Ramesh, Bhashyam, Cohen, Steven B., Catozzi, John R.
• Primary Examiner(s): Wu; Yicun
• Application Number:
  US10/256,712
• Publication Number:
  US 20040062106A1
• Time in Patent Office: 1,656 Days
• Field of Search: 707 1- 10, 707100-1041, 707200-203, 707/205, 715/792, 711/134, 711/137, 711/165
• US Class Current: 707/704
• CPC Class Codes: G06F 16/24552 Database cache management
• CPC Class Codes: Y10S 707/99931 Database or file accessing
• CPC Class Codes: Y10S 707/99932 Access augmentation or optimizing
• CPC Class Codes: Y10S 707/99936 Pattern matching access
• CPC Class Codes: Y10S 707/99942 Manipulating data structure, e.g. compression, compaction, compilation
• CPC Class Codes: Y10S 707/99943 Generating database or data structure, e.g. via user interface

Abstract

A method for retrieving information from a database includes identifying a cylinder. The cylinder includes a plurality of data segments. The method also includes retrieving the plurality of data segments from the cylinder during a single retrieval operation. In addition, the method includes storing the plurality of data segments in a cache.

Claims

1. A method for retrieving information from a database, the method comprising:

receiving a request to retrieve a first plurality of data segments associated with a table in the database;

identifying a cylinder comprising a second plurality of data segments, the second plurality of data segments including the first plurality of data segments;

determining if the first plurality of data segments exceeds a threshold number of data segments;

retrieving the second plurality of data segments during a single retrieval operation if the first plurality of data segments exceeds the threshold number of data segments; and

storing the retrieved data segments in a cache.

2. The method of claim 1, further comprising:

generating a segment descriptor block for each of at least some of the retrieved data segments,

wherein each segment descriptor block identifies a location of a corresponding data segment in the cache.

3. The method of claim 2, wherein each segment descriptor block further comprises a lock to limit access to the respective segment descriptor block by two or more processes.

4. The method of claim 2, wherein a segment descriptor block is generated only for each of the first plurality of data segments.

5. The method of claim 2, wherein each segment descriptor block identifies a starting virtual address and a size of the corresponding data segment in the cache.

6. The method of claim 2, further comprising:

inserting each segment descriptor block into at least one of a plurality of first chains.

7. The method of claim 6, further comprising:

moving a segment descriptor block from at least one of the plurality of first chains to one of a plurality of second chains when the associated data segment is accessed.

8. The method of claim 7, further comprising:

moving the segment descriptor block from the one of the plurality of second chains back to the at least one of the plurality of first chains when the associated data segment is no longer being accessed.

9. The method of claim 6, wherein each of the plurality of first chains comprises an age chain containing segment descriptor blocks associated with data segments that are not currently being accessed.

10. The method of claim 7, wherein each of the plurality of second chains comprises an access chain containing segment descriptor blocks associated with data segments that are currently being accessed.

11. The method of claim 1, wherein the threshold number of data segments is greater than or equal to eight.

12. The method of claim 11, wherein the threshold number of data segments is less than or equal to eleven.

13. A method for retrieving information from a database, the method comprising:

receiving a request to retrieve a first plurality of data segments associated with a table in the database;

identifying a cylinder comprising a second plurality of data segments, the second plurality of data segments including the first plurality of data segments;

determining if a ratio of the first plurality of data segments to the second plurality of data segments exceeds a threshold value;

retrieving the second plurality of data segments during a single retrieval operation if the ratio of the first plurality of data segments to the second plurality of data segments exceeds the threshold value; and

storing the retrieved data segments in a cache.

14. A system for retrieving information from a database, the system comprising:

at least one computer readable medium; and

logic encoded on the at least one computer readable medium, the logic operable when executed to;

receive a request to retrieve a first plurality of data segments associated with a table in the database;

identify a cylinder comprising a second plurality of data segments, the second plurality of data segments including the first plurality of data segments;

determine if the first plurality of data segments exceeds a threshold number of data segments;

retrieve the second plurality of data segments during a single retrieval operation if the first plurality of data segments exceeds the threshold number of data segments; and

store the retrieved data segments in a cache.

15. The system of claim 14, wherein the logic is further operable to:

generate a segment descriptor block for each of at least some of the retrieved data segments,

wherein each segment descriptor block identifies a location of a corresponding data segment in the cache.

16. The system of claim 15, wherein each segment descriptor block further comprises a lock to limit access to the respective segment descriptor block by two or more processes.

17. The system of claim 15, wherein a segment descriptor block is generated only for each of the first plurality of data segments.

18. The system of claim 15, wherein each segment descriptor block identifies a starting virtual address and a size of the corresponding data segment in the cache.

19. The system of claim 15, wherein the logic is further operable to:

insert each segment descriptor block into at least one of a plurality of first chains.

20. The system of claim 19, wherein the logic is further operable to:

move a segment descriptor block from at least one of the plurality of first chains to one of a plurality of second chains when the associated data segment is accessed.

21. The system of claim 20, wherein the logic is further operable to:

move the segment descriptor block from the one of the plurality of second chains back to the at least one of the plurality of first chains when the associated data segment is no longer being accessed.

22. The system of claim 19, wherein each of the plurality of first chains comprises an age chain containing segment descriptor blocks associated with data segments that are not currently being accessed.

23. The system of claim 20, wherein each of the plurality of second chains comprises an access chain containing segment descriptor blocks associated with data segments that are currently being accessed.

24. The system of claim 14, wherein the threshold number of data segments is greater than or equal to eight.

25. The system of claim 24, wherein the threshold number of data segments is less than or equal to eleven.

26. A system for retrieving information from a database, the system comprising:

at least one computer readable medium; and

logic encoded on the at least one computer readable medium, the logic operable when executed to;

receive a request to retrieve a first plurality of data segments associated with a table in the database;

identify a cylinder comprising a second plurality of data segments, the second plurality of data segments including the first plurality of data segments;

determine if a ratio of the first plurality of data segments to the second plurality of data segments exceeds a threshold value;

retrieve the second plurality of data segments during a single retrieval operation if the ratio of the first plurality of data segments to the second plurality of data segments exceeds the threshold value; and

store the retrieved data segments in a cache.