GLOBAL CHECKPOINT SCN

• US 20100036843A1
• Filed: 10/02/2008
• Published: 02/11/2010
• Est. Priority Date: 08/08/2008
• Status: Active Grant

• Current Assignee: Oracle International Corporation (Oracle Corporation)
• Original Assignee: Oracle International Corporation (Oracle Corporation)
• Inventors: Lahiri, Tirthankar, Malhotra, Varun, MacNaughton, Neil
• Granted Patent: US 7,991,775 B2
• Time in Patent Office: Days
• US Class Current: N/A
• CPC Class Codes: G06F 16/2343 Locking methods, e.g. distributed locking or locking implementation details
• CPC Class Codes: Y10S 707/99933 Query processing, i.e. searching
• CPC Class Codes: Y10S 707/99935 Query augmenting and refining, e.g. inexact access

Abstract

Described herein are techniques for generating a global checkpoint system change number and computing a snapshot query using the global checkpoint system change number without a need to acquire global locks. In many cases, the need to acquire global locks is eliminated, thereby saving the overhead attendant to processing global locks.

Claims

1. A computer-implemented method, comprising:

a multi-node database server computing a snapshot query associated with a snapshot time;

generating a global checkpoint system change number, wherein any data block in said database that is associated with a system change number that is less than said global checkpoint system change number is stored persistently in the database;

wherein computing said snapshot query comprises;

determining whether said snapshot time is less than said global checkpoint system change number;

when said snapshot time is less than said global checkpoint system change number, then accessing said data blocks in the database without obtaining a global lock for any of said data blocks; and

when said snapshot time is greater than said global checkpoint system change number, obtaining a global lock for each data block of data blocks before accessing said data block in the database.

2. The method of claim 1,

wherein each node of said multi-node database server maintains a list of dirty data blocks, each data block of said list of dirty data blocks being associated with a system change number of a change to said each data block;

and

wherein the step of generating a global checkpoint system number further comprises determining a minimum system change number of said system change numbers associated with said list of dirty data blocks.

3. The method of claim 2, wherein the step of a generating a global checkpoint system change number further comprises:

said each node of said multi-node database server generating a checkpoint system change number, wherein any data block that is associated with a system change number generated by said each node that is less than the checkpoint system change number of said node has been stored persistently by said each node; and

determining a minimum of the checkpoint system change numbers generated by the nodes of said multi-node database server.

8. A computer-readable storage medium storing one or more sequences of instructions which, when executed by one or more processors, causes the one or more processors to perform the method recited in claim 1.

9. A computer-readable storage medium storing one or more sequences of instructions which, when executed by one or more processors, causes the one or more processors to perform the method recited in claim 2.

10. A computer-readable storage medium storing one or more sequences of instructions which, when executed by one or more processors, causes the one or more processors to perform the method recited in claim 3.

4. A computer-implemented method, comprising:

each node of a multi-node database server generating a checkpoint system change number, wherein any data block that is associated with a system change number generated by said each node that is less than the checkpoint system change number of said node has been stored persistently by said each node; and

generating a global checkpoint system change number by determining a minimum of the checkpoint system change numbers generated by the nodes of said multi-node database server.

5. The method of claim 4, further comprising:

computing a snapshot query associated with a snapshot time,

wherein computing said snapshot query comprises;

determining whether said snapshot time is less than said global checkpoint system change number;

when said snapshot time is less than said global checkpoint system change number, then accessing said data blocks in the database without obtaining a global lock for any of said data blocks.

6. The method of claim 4, further comprising:

computing a snapshot query associated with a snapshot time,

wherein computing said snapshot query comprises;

determining whether said snapshot time is greater than said global checkpoint system change number;

when said snapshot time is greater than said global checkpoint system change number, obtaining a global lock for each data block of data blocks before accessing said data block in the database.

7. The method of claim 5,

wherein each node of said multi-node database server maintains a list of dirty data blocks, each data block of said list of dirty data blocks being associated with the system change number of a change to said each data block;

and

wherein determining a minimum of the checkpoint system change numbers further comprises determining a minimum system change number of said system change numbers associated with said list of dirty data blocks.

11. A computer-readable storage medium storing one or more sequences of instructions which, when executed by one or more processors, causes the one or more processors to perform the method recited in claim 4.

12. A computer-readable storage medium storing one or more sequences of instructions which, when executed by one or more processors, causes the one or more processors to perform the method recited in claim 5.

13. A computer-readable storage medium storing one or more sequences of instructions which, when executed by one or more processors, causes the one or more processors to perform the method recited in claim 6.

14. A computer-readable storage medium storing one or more sequences of instructions which, when executed by one or more processors, causes the one or more processors to perform the method recited in claim 7.