查看当前的连接数：
select count(*) from v$process
查看数据库允许的最大连接数：
select value from v$parameter where name = 'processes'
修改最大连接数：
alter system set processes = 300 scope = spfile
查看会话数：
select count(*) from v$session
查看活动会话数：
select count(*) from v$session where status='ACTIVE'
查看当前有哪些用户正在使用数据：
SELECT osuser, a.username,cpu_time/executions/1000000||'s', sql_fulltext,machine from v$session a, v$sqlarea b where a.sql_address =b.address order by cpu_time/executions desc