1：
SQL> alter system set sga_max_size=50m scope=spfile;
系统已更改。
这样改动正常!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
2：
这样改动报错？？？？？？？？？？？？？？？？？？？？？？？？？？？？？？？？？？？
SQL> alter system set sga_max_size=40m scope=both;
alter system set sga_max_size=40m scope=both
在Oracle中，從9i開始引入了spfile，也就是服務 器端初始化參數，有很多是可以支持在線修改的，也就是修改會馬上生效，詳細內容看下面的說明：
The ISSYS_MODIFIABLE column in V$PARAMETER tells us whether the parameters are static or dynamic. Static parameters require the instance to be restarted while dynamic parameters can take effect immediately upon being changed.
SQL> select distinct issys_modifiable from v$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 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.
BANNER
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Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Prod
PL/SQL Release 10.2.0.1.0 - Production
CORE10.2.0.1.0Production
TNS for 32-bit Windows: Version 10.2.0.1.0 - Production
NLSRTL Version 10.2.0.1.0 - Production
SQL> Select Name,isses_modifiable,issys_modifiable,isinstance_modifiable From v$parameter Where Name='sga_max_size';
