| 摘要 |
A method, computer program product, and system for providing access to a database object during modification of that object. Upon receipt of a data definition language (DDL) operation specifying a modification to the database object, currently executing database transactions are invalidated in a two-step process of a soft invalidation followed by a hard invalidation. The soft invalidation permits the current database transactions to continue executing while modifying the logical structure of the database object in accordance with the DDL operation, and the hard invalidation waits for the database transactions started prior to the DDL operation to finish execution before modifying the physical structure of the database object in accordance with the DDL operation. After the modification to the logical structure is complete, new database transactions are allowed to execute against the modified database object, thus improving the availability of the object while it is being modified.
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