动态参数,静态参数
静态参数： 修改后必须重启才能生效
动态参数：修改后立即生效
当使用spfile的情况下，动态和静态参数都可以通过：
Alter system 全部会话有效.
Alter system set xxx=xxx; 同时更新spfile和memory内容
Alter system set xxx=xxx scope = spfile|memory; 只更新一个地方的.
对于动态参数，还可以通过
Alter session set xxx=xxx; 来修改参数值，但只对当前会话有效.
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 ----表明为静态的
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 of the instance; the database needs to be restarted for changes to take effect.
A parameter set to IMMEDATE value means that it is dynamic and can be set to change the present active instance as well as future database restarts.
A parameter set to DEFERRED is also dynamic, but changes only affect subsequent sessions, currently active sessions will not be affected and retain the old parameter value.
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