Oracle notices when a DML object or system privilege is granted to or revoked from a
user or PUBLIC and automatically invalidates all the owner’s dependent objects.
Oracle invalidates the dependent objects to verify that an owner of a dependent object
continues to have the necessary privileges for all referenced objects. Internally, Oracle
notes that such objects do not have to be recompiled. Only security authorizations
need to be validated, not the structure of any objects. This optimization eliminates
unnecessary recompilations and prevents the need to change a dependent object’s time
stamp.

安全授权
1. 当对某个对象赋予或者收回权限时 ，依赖对象被置为失效对象
2. Oracle 会验证用户的依赖对象是否具备必要的权限来访问所需的引用对象 ,并认为此类无效对象不需要重新编译