select * from v$session where username is not null

select username,count(username) from v$session where username is not null group by username #查看不同用户的连接数 

select count(*) from v$session   #连接数

Select count(*) from v$session where status='ACTIVE'　#并发连接数

show parameter processes   #最大连接

alter system set processes = value scope = spfile;重启数据库   #修改连接

/home/oracle9i/app/oracle9i/dbs/init.ora

/home/oracle9i/app/oracle9i/dbs/spfilexxx.ora ## open_cursor