Oracle赋权的回收权限是使用grant和revoke语句，但是赋权和回收权限语句执行完成后就会立即生效么？另外Oracle的权限又分为系统权限、角色权限和对象权限，这三种权限的grant和revoke生效时间又是怎样的呢。我们来看官方文档是如何说的：
Depending on what is granted or revoked, a grant or revoke takes effect at different times:
-
All grants and revokes of system and object privileges to anything (users, roles, and
PUBLIC) take immediate effect. -
All grants and revokes of roles to anything (users, other roles,
PUBLIC) take effect only when a current user session issues aSET ROLEstatement to reenable the role after the grant and revoke, or when a new user session is created after the grant or revoke.
You can see which roles are currently enabled by examining the SESSION_ROLES data dictionary view.
从上面的描述中我们可以知道，grant和revoke系统权限和对象权限时会立即生效，而grant或revoke角色时对当前会话不会立即生效，除非使用set role语句启用角色或重新连接会话后设置才会生效。
下面以11.2.0.4为例做一个测试，是否与官方文档描述的一致。
一、首先创建一个测试用户，赋予connect角色
sys@ORCL>create user zhaoxu identified by zhaoxu;
User created.
sys@ORCL>grant connect to zhaoxu;
Grant succeeded.
sys@ORCL>select * from dba_role_privs where grantee='ZHAOXU';
GRANTEE GRANTED_ROLE ADMIN_OPT DEFAULT_R
------------------------------ ------------------------------ --------- ---------
ZHAOXU CONNECT NO YES
sys@ORCL>select * from dba_sys_privs where grantee='ZHAOXU';
no rows selected
sys@ORCL>select * from dba_tab_privs where grantee='ZHAOXU';
no rows selected
sys@ORCL>conn zhaoxu/zhaoxu
Connected.
zhaoxu@ORCL>select * from session_roles;
ROLE
------------------------------------------------------------
CONNECT
zhaoxu@ORCL>select * from session_privs;
PRIVILEGE
------------------------------------------------------------
CREATE SESSION
zhaoxu@ORCL>create table t (id number) segment creation immediate;
create table t (id number)
*
ERROR at line 1:
ORA-01031: insufficient privileges
现在的zhaoxu用户只有CONNECT角色，只能连接到数据库，其他基本什么都做不了。
二、测试系统权限和对象权限的grant和revoke
现在打开另一个会话赋予system privilege给zhaoxu用户
--session 2
sys@ORCL>grant create table,unlimited tablespace to zhaoxu;
Grant succeeded.
--session 1
zhaoxu@ORCL>select * from session_privs;
PRIVILEGE
------------------------------------------------------------------------------------------------------------------------
CREATE SESSION
UNLIMITED TABLESPACE
CREATE TABLE
zhaoxu@ORCL>select * from session_roles;
ROLE
------------------------------------------------------------------------------------------
CONNECT
zhaoxu@ORCL>create table t (id number) segment creation immediate;
Table created.
--使用segment creation immediate是因为要避免11g的新特性段延迟创建造成影响
在赋予zhaoxu用户create table和unlimited tablespace系统权限全会话1没有做任何操作，权限就会立即生效。
再测试revoke权限的情况
--session 2
sys@ORCL>revoke unlimited tablespace from zhaoxu;
Revoke succeeded.
--session 1
zhaoxu@ORCL>create table t1 (id number) segment creation immediate;
create table t1 (id number) segment creation immediate
*
ERROR at line 1:
ORA-01950: no privileges on tablespace 'USERS'
zhaoxu@ORCL>select * from session_privs;
PRIVILEGE
------------------------------------------------------------------------------------------------------------------------
CREATE SESSION
CREATE TABLE
同样可以看到回收操作可以立即生效，现有session无需做任何操作。
测试对象权限的grant和revoke
--grant测试
--session 1
zhaoxu@ORCL>select count(*) from zx.t;
select count(*) from zx.t
*
ERROR at line 1:
ORA-00942: table or view does not exist
--session 2
sys@ORCL>grant select on zx.t to zhaoxu;
Grant succeeded.
sys@ORCL>select * from dba_tab_privs where grantee='ZHAOXU';
GRANTEE OWNER TABLE_NAME GRANTOR PRIVILEGE GRANTABLE HIERARCHY
------------------------------ ------------------------------ ---------- ---------- ---------- --------- ---------
ZHAOXU ZX T ZX SELECT NO NO
--session 1
zhaoxu@ORCL>select count(*) from zx.t;
COUNT(*)
----------
99999
zhaoxu@ORCL>select * from session_privs;
PRIVILEGE
------------------------------------------------------------------------------------------------------------------------
CREATE SESSION
CREATE TABLE
--revoke测试
--session 2
sys@ORCL>revoke select on zx.t from zhaoxu;
Revoke succeeded.
sys@ORCL>select * from dba_tab_privs where grantee='ZHAOXU';
no rows selected
--session 1
zhaoxu@ORCL>select count(*) from zx.t;
select count(*) from zx.t
*
ERROR at line 1:
ORA-00942: table or view does not exist
对对象权限的grant和revoke操作与系统权限的一致，所有的命令都是立即生效，包括对已经连接的会话。
三、测试角色的grant和revoke
现在的zhaoxu用户仍然只有connect角色，并且已经打开一个会话
--session 2
sys@ORCL>select * from dba_role_privs where grantee='ZHAOXU';
GRANTEE GRANTED_ROLE ADMIN_OPT DEFAULT_R
------------------------------ ------------------------------ --------- ---------
ZHAOXU CONNECT NO YES
--session 1
zhaoxu@ORCL>select * from session_roles;
ROLE
------------------------------------------
CONNECT
测试grant DBA权限
--session 1查看会话中的角色
zhaoxu@ORCL>select * from session_roles;
ROLE
------------------------------------------------------------------------------------------
CONNECT
--session 2赋予zhaoxu用户dba角色
sys@ORCL>grant dba to zhaoxu;
Grant succeeded.
sys@ORCL>select * from dba_role_privs where grantee='ZHAOXU';
GRANTEE GRANTED_ROLE ADMIN_OPT DEFAULT_R
------------------------------ ------------------------------ --------- ---------
ZHAOXU DBA NO YES
ZHAOXU CONNECT NO YES
--session 1再次查看会话中的角色，没有dba角色，也没有查看v$session的权限
zhaoxu@ORCL>select * from session_roles;
ROLE
------------------------------------------------------------------------------------------
CONNECT
zhaoxu@ORCL>select count(*) from v$session;
select count(*) from v$session
*
ERROR at line 1:
ORA-00942: table or view does not exist
--session 1执行set role命令，可以看到DBA及相关的角色已经加载到session1中了，也可以查询v$session
zhaoxu@ORCL>set role dba;
Role set.
zhaoxu@ORCL>select * from session_roles;
ROLE
------------------------------------------------------------------------------------------
DBA
SELECT_CATALOG_ROLE
HS_ADMIN_SELECT_ROLE
......
19 rows selected.
zhaoxu@ORCL>select count(*) from v$session;
COUNT(*)
----------
29
--使用zhaoxu用户打开session 3，可以看到新会话中默认会加载DBA及相关角色
[oracle@rhel6 ~]$ sqlplus zhaoxu/zhaoxu
SQL*Plus: Release 11.2.0.4.0 Production on Sat Jan 21 16:22:01 2017
Copyright (c) 1982, 2013, Oracle. All rights reserved.
Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
zhaoxu@ORCL>select * from session_roles;
ROLE
------------------------------------------------------------------------------------------
CONNECT
DBA
SELECT_CATALOG_ROLE
......
20 rows selected.
测试revoke DBA角色
--session 2回收DBA角色
sys@ORCL>revoke dba from zhaoxu;
Revoke succeeded.
sys@ORCL>select * from dba_role_privs where grantee='ZHAOXU';
GRANTEE GRANTED_ROLE ADMIN_OPT DEFAULT_R
------------------------------ ------------------------------ --------- ---------
ZHAOXU CONNECT NO YES
--session 3查看会话的角色，仍然有DBA及相关角色
zhaoxu@ORCL>select * from session_roles;
ROLE
------------------------------------------------------------------------------------------
CONNECT
DBA
SELECT_CATALOG_ROLE
......
20 rows selected.
--使用zhaoxu用户打开session 4，查看只有CONNECT角色
[oracle@rhel6 ~]$ sqlplus zhaoxu/zhaoxu
SQL*Plus: Release 11.2.0.4.0 Production on Sat Jan 21 16:30:19 2017
Copyright (c) 1982, 2013, Oracle. All rights reserved.
Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
zhaoxu@ORCL>select * from session_roles;
ROLE
------------------------------------------------------------------------------------------
CONNECT
--session 3执行set role命令
zhaoxu@ORCL>set role dba;
set role dba
*
ERROR at line 1:
ORA-01924: role 'DBA' not granted or does not exist
zhaoxu@ORCL>set role all;
Role set.
zhaoxu@ORCL>select * from session_roles;
ROLE
------------------------------------------------------------------------------------------
CONNECT
从上面的测试中可以总结出，grant和revoke系统权限和对象权限时会立即生效，而grant或revoke角色时对当前会话不会立即生效，除非使用set role语句启用角色或重新连接会话后设置才会生效。与官方文档的描述一致。
但是有一个问题是如果查看已经连接的其他会话所拥有的role呢？
官方文档：docs.oracle.com/cd/E11882_0…
system privilege:docs.oracle.com/cd/E11882_0…
object privilege:docs.oracle.com/cd/E11882_0…
set role:docs.oracle.com/cd/E11882_0…
