记下方便查询使用：

–当前的数据库连接数

select count(*) from v$process

–数据库允许的最大连接数

select value from v$parameter where name = 'processes';

or

show parameter processes;

–修改最大连接数

alter system set processes = value scope = spfile; 

–重启数据库

shutdown immediate;

startup;

–查看当前有哪些用户正在使用数据库

SELECT osuser, a.username,cpu_time/executions/1000000||'s', b.sql_text,machine
from v$session a, v$sqlarea b
where a.sql_address =b.address order by cpu_time/executions desc;

–当前的session连接数 

select count(*) from v$session   

–并发连接数

select count(*) from v$session where status='ACTIVE';