| 摘要 |
A fine-grained access control mechanism uses policy functions that are associated with a database object (e.g. table and view). The policy functions are invoked, when, for example, a database server detects that a query is issued against the database object. The value of a policy function remains constant under certain conditions. For example, once a database server is brought up, the value of a policy function may remain the same. Users can specify the conditions under which the value of a policy function remain constant. Based on this information, when a policy function is computed while processing a query, the database server caches the value of the policy function. When processing another query that requires the value of the policy function, the database server retrieves the result from the cache rather than re-computing the policy function, as long as the condition under which the policy function remains constant persists.
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