今天按照Oracle Support的建议设置event的时候发现set event和set events这两种写法效果不一样，防止忘记先记下来。
1. alter system set event ：此方法对spfile生效，无法对memory生效
SQL> ALTER system SET event='1461 trace name errorstack level 3'; ALTER system SET event='1461 trace name errorstack level 3' * ERROR at line 1: ORA-02095: specified initialization parameter cannot be modified SQL> ALTER system SET event='1461 trace name errorstack level 3' scope=spfile; System altered.
验证是否已成功更改：
SQL> CREATE pfile='/home/oracle/1.ora' FROM spfile; File created. SQL> !
[oracle@rac01 ~]$ grep event 1.ora *.event='1461 trace name errorstack level 3'
这种方法的话，需要重启DB。下面Rollback这个参数更改
SQL> ALTER system SET event='1461 trace name errorstack off' scope=spfile; System altered. SQL> CREATE pfile='/home/oracle/2.ora' FROM spfile; File created. SQL> !
[oracle@rac01 ~]$ grep event 2.ora *.event='1461 trace name errorstack off'
2. alter system set events：此方法对memory生效，无法对spfile生效
SQL> ALTER system SET events '1461 trace name errorstack level 3'; System altered. SQL> !
验证：
[oracle@rac01 ~]$ tail -n1 /oracle/admin/strm1/bdump/alert_strm1.log OS Pid: 9070 executed alter system set events '1461 trace name errorstack level 3'
这个参数更改没有反应到spfile中
SQL> CREATE pfile='/home/oracle/3.ora' FROM spfile; File created. SQL> !
[oracle@rac01 ~]$ grep event 3.ora *.event='1461 trace name errorstack off'
其实这里的1461是个BUG 6085625，Metalink上可以参照NOTE: 461911.1
另外需要注意的是，RAC环境中用方法2动态设置event的话需要在所有instance设置。不过理解了上面的区别的话这个也就很容易明白了。
注意：设置1461 event无法对已经存在的进程生效，对于设置之后新建立的进程才会有效果。所以，不得不，我们还是得重启DB，让其对所有进程生效。
