在Oracle中，从9i开始引入了spfile，也就是服务 器端初始化参数，有很多是可以支持在线修改的，也就是修改会马上生效，详细内容看下面的说明：

The ISSYS_MODIFIABLE column in V$PARAMETER tells us whether the parameters are static or dynamic. Static parameters require the instance to be restarted while dynamic parameters can take effect（生效） immediately upon（在…之后） being changed.

SQL> select distinct issys_modifiable from v$parameter;

ISSYS_MODIFIABLE

—————————

DEFERRED

FALSE

IMMEDIATE

If the ISSYS_MODIFIABLE value is set to FALSE for a parameter, it means that the parameter cannot change its value in the lifetime（一生） of the instance; the database needs to be restarted for changes to take effect（生效）.

A parameter set to IMMEDATE value means that it is dynamic（动态的） and can be set to change the present（当前） active instance as well as future database restarts.

A parameter set to DEFERRED is also dynamic, but changes only affect（生效） subsequent（后来的） sessions, currently active sessions will not be affected and retain（保持） the old parameter value.

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