Each session that references a package construct has its own instance of that package,
including a persistent state of any public and private variables, cursors, and constants.
All of a session’s package instantiations including state can be lost if any of the
session’s instantiated packages are subsequently invalidated and recompiled.
每个与包的组成物相关的会话拥有它自己关于那个包的实例信息，包含一个关于公有和私
有的变量，游标和常量的持续状态。会话的包的实例话所有包含状态信息可能丢失如果会
话的实例话包相继变为失效和被重新编译。
