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 a SET ROLE statement 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    YESsys@ORCL>select * from dba_sys_privs where grantee='ZHAOXU';no rows selectedsys@ORCL>select * from dba_tab_privs where grantee='ZHAOXU';no rows selectedsys@ORCL>conn zhaoxu/zhaoxu
Connected.
zhaoxu@ORCL>select * from session_roles;ROLE
------------------------------------------------------------
CONNECTzhaoxu@ORCL>select * from session_privs;PRIVILEGE
------------------------------------------------------------
CREATE SESSIONzhaoxu@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 TABLEzhaoxu@ORCL>select * from session_roles;ROLE
------------------------------------------------------------------------------------------
CONNECTzhaoxu@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(*)
----------99999zhaoxu@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$session的权限
zhaoxu@ORCL>select * from session_roles;ROLE
------------------------------------------------------------------------------------------
CONNECTzhaoxu@ORCL>select count(*) from v$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/zhaoxuSQL*Plus: Release 11.2.0.4.0 Production on Sat Jan 21 16:22:01 2017Copyright (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 optionszhaoxu@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/zhaoxuSQL*Plus: Release 11.2.0.4.0 Production on Sat Jan 21 16:30:19 2017Copyright (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 optionszhaoxu@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 existzhaoxu@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：http://docs.oracle.com/cd/E11882_01/network.112/e36292/authorization.htm#DBSEG99974

system privilege:http://docs.oracle.com/cd/E11882_01/server.112/e41084/statements_9013.htm#BABEFFEE

object privilege:http://docs.oracle.com/cd/E11882_01/server.112/e41084/statements_9013.htm#BGBCIIEG

set role:http://docs.oracle.com/cd/E11882_01/server.112/e41084/statements_10004.htm#SQLRF01704