Oracle动态性能视图 v$parameter 和 v$parameter2 的区别

v$parameter 的说明见这里：

V$PARAMETER displays information about the initialization parameters that are currently in effect for the session.

v$parameter2 的说明见这里：

V$PARAMETER2 displays information about the initialization parameters that are currently in effect for the session, with each list parameter value appearing as a row in the view.

区别在于这句：

with each list parameter value appearing as a row in the view
每个列表参数值在视图中显示为一行

看一个实际的例子。环境为2节点RAC。

select count(*) from v$parameter; 
  COUNT(*)
----------
       458

select count(*) from v$parameter2;
  COUNT(*)
----------
       463

显然，v$parameter2的行数更多。来看一下多的原因。

第一种可能是，v$parameter2中有的参数，在v$parameter中没有。确实找到了3个。

select name from v$parameter2
minus
select name from v$parameter;

NAME                                                                            
--------------------------------------------------------------------------------
asm_diskgroups
asm_io_processes
asm_power_limit

第二种可能是，在v$parameter中出现1次的参数，在v$parameter2中出现了多次。确实找到了2个：

select name, count(*) from v$parameter2 group by name having count(*) > 1;

NAME                                                                               COUNT(*)
-------------------------------------------------------------------------------- ----------
control_files                                                                             2
connection_brokers                                                                        2

这样就对上了：

$ bc <<< 458+2+3
463

看一下这几个参数在两个表中的实际值：

SQL> select name, value from v$parameter where name in ('control_files', 'connection_brokers');

                 NAME                                                                                               VALUE
_____________________ ___________________________________________________________________________________________________
control_files         +DATAC1/ORCL/CONTROLFILE/current.692.1155482173, +RECOC1/ORCL/CONTROLFILE/current.623.1155482173
connection_brokers    ((TYPE=DEDICATED)(BROKERS=1)), ((TYPE=EMON)(BROKERS=1))

SQL> select name, value from v$parameter2 where name in ('control_files', 'connection_brokers');

                 NAME                                              VALUE
_____________________ __________________________________________________
control_files         +DATAC1/ORCL/CONTROLFILE/current.692.1155482173
control_files         +RECOC1/ORCL/CONTROLFILE/current.623.1155482173
connection_brokers    ((TYPE=DEDICATED)(BROKERS=1))
connection_brokers    ((TYPE=EMON)(BROKERS=1))

SQL> select name, value from v$parameter where name in ('asm_diskgroups', 'asm_io_processes', 'asm_power_limit');

no rows selected

SQL> select name, value from v$parameter2 where name in ('asm_diskgroups', 'asm_io_processes', 'asm_power_limit');

               NAME    VALUE
___________________ ________
asm_diskgroups
asm_power_limit     1
asm_io_processes    20

注意：asm的这3个参数，可以登录到ASM实例中查看。