1.當前的數據庫連接數
select count(*) from v$process where program=‘ORACLE.EXE(SHAD)‘; 

2.數據庫允許的最大連接數
select value from v$parameter where name =‘processes‘

3.修改最大連接數，需要重啟數據庫才能生效:
alter system set processes = 300 scope = spfile;

4.重啟數據庫
shutdown immediate;
startup;

5.查看當前有哪些用戶正在使用數據
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/executionsdesc;

6.當前的session連接數  
select count(*) from v$session  

7.並發連接數
select count(*) from v$session where status=‘ACTIVE‘　

8.最大連接
show parameter processes  

oracle查詢數據庫最大連接數等信息