grant revoke dba生效时间

前段时间，做了个实现，发现grant revoke dba权限给一个用户，对已连接的会话不生效，只有之后连接进数据库的session才生效。而grant select on owner.table_name to username，对已连接的会话是即使生效的，具体测试过程如下：
[code]-----session1
SQL> create user dba_test identified by oracle;

User created.

Elapsed: 00:00:00.11
SQL> alter user dba_test account unlock;

User altered.

Elapsed: 00:00:00.05
SQL> grant connect to dba_test;

Grant succeeded.

Elapsed: 00:00:00.07

------session2
SQL> conn dba_test/oracle
Connected.
SQL> select count(*) from dba_tables;
select count(*) from dba_tables
*
ERROR at line 1:
ORA-00942: table or view does not exist


Elapsed: 00:00:00.02

-----------session1
SQL> grant dba to dba_test;

Grant succeeded.

Elapsed: 00:00:00.04

-----------session2
SQL> select count(*) from dba_tables;
select count(*) from dba_tables
*
ERROR at line 1:
ORA-00942: table or view does not exist


Elapsed: 00:00:00.01

-----------session1
SQL> grant select on dba_tables to dba_test;

Grant succeeded.
-----------session2
SQL> select count(*) from dba_tables;

COUNT(*)
----------
3245

Elapsed: 00:00:00.23
--------session2

SQL> conn dba_test/oracle
Connected.
SQL> show user;
USER is "DBA_TEST"
SQL> select count(*) from dba_views;

COUNT(*)
----------
5302
---------session1
SQL> revoke dba from dba_test;

Revoke succeeded.
--------session2
SQL> select count(*) from dba_views;

COUNT(*)
----------
5302

Elapsed: 00:00:00.03
SQL> conn / as sysdba
Connected.
SQL> conn dba_test/oracle
Connected.
SQL> select count(*) from dba_views;
select count(*) from dba_views
*
ERROR at line 1:
ORA-00942: table or view does not exist[/code]