Global checkpoint SCN
First Claim
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1. A computer-implemented method, comprising:
- a multi-node database server computing a snapshot query associated with a snapshot time, wherein said multi-node database server manages access to a database comprising database data blocks;
said multi-node database server generating a global checkpoint system change number, wherein any data block of said database data blocks that is associated with a system change number that is less than said global checkpoint system change number is stored persistently in said database;
wherein computing said snapshot query comprises;
said multi-node database server 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, said multi-node database server accessing data blocks of said database data blocks without obtaining a global lock for any of said data blocks of said database data blocks; and
when said snapshot time is greater than said global checkpoint system change number, said multi-node database server accessing data blocks of said database data blocks, and obtaining a global lock on said data blocks of said database data blocks to access any of said data block of said database data blocks.
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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.
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Citations
14 Claims
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1. A computer-implemented method, comprising:
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a multi-node database server computing a snapshot query associated with a snapshot time, wherein said multi-node database server manages access to a database comprising database data blocks; said multi-node database server generating a global checkpoint system change number, wherein any data block of said database data blocks that is associated with a system change number that is less than said global checkpoint system change number is stored persistently in said database; wherein computing said snapshot query comprises; said multi-node database server 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, said multi-node database server accessing data blocks of said database data blocks without obtaining a global lock for any of said data blocks of said database data blocks; and when said snapshot time is greater than said global checkpoint system change number, said multi-node database server accessing data blocks of said database data blocks, and obtaining a global lock on said data blocks of said database data blocks to access any of said data block of said database data blocks. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A computer-implemented method, comprising:
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each node of a multi-node database server, that manages access to a database comprising database data blocks, generating a checkpoint system change number, wherein any data block of said database data blocks 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 in said database by said each node; and said multi-node database server 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. - View Dependent Claims (8, 9, 10, 11, 12, 13, 14)
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Specification