TAF是Transparent Application Failover的英文缩写，顾名思义就是对应用透明的故障转移，举个例子，当应用连接某个oracle数据库的执行查询操作的时候，数据库服务器网络中断或者实例崩溃，在经过delay参数设置的值之后，将自动连接到其他可用的实例，继续进行查询。(前提是执行计划，输出结果集和输出的顺序不能发生变化)

TAF的特性：
1：TAF是ORACLE客户端提供的一项特性，使用TAF，对客户端的环境有一定的要求，比如JAVA的JDBC驱动、Oracle客户端的版本等（8i开始支持TAF)；
2：大致上TAF可以分为2种，连接时的TAF和会话建立后TAF；
3：TAF本身与是否RAC环境无关，但一般都用在RAC环境，最小程度的减少最应用的影响，单实例环境下也可以使用TAF，这样使用PL/SQL developer连接数据库，即使数据库实例重启，也不需要重新连接；
4：RAC环境下，还可以把TAF配置在服务器端；
5：配置listener.ora文件的GLOBAL_DBNAME参数后将会禁用TAF

扩展阅读：
http://www.laoxiong.net/taf_part1.html

http://www.laoxiong.net/taf_part2.html

http://www.laoxiong.net/taf_part3.html

一：RAC环境下配置连接时的TAF，客户端为rhel6，当节点2关闭后，新建立的连接会连接到节点1

1. [root@rhel6 ~]# su - oracle  
2. [oracle@rhel6 ~]$ cd $ORACLE_HOME/network/admin  
3. [oracle@rhel6 admin]$ tail  tnsnames.ora   
4. RAC4 =  
5.   (DESCRIPTION =  
6.     (ADDRESS = (PROTOCOL = TCP)(HOST = rac1-vip.yang.com)(PORT = 1521))  
7.     (ADDRESS = (PROTOCOL = TCP)(HOST = rac2-vip.yang.com)(PORT = 1521))  
8.     (LOAD_BALANCE = yes)  
9.     (FAILOVER = yes)  
10.     (CONNECT_DATA =  
11.       (SERVER = DEDICATED)  
12.       (SERVICE_NAME = rac.yang.com)  
13.     )  
14. )  
15.  
16. [oracle@rhel6 admin]$ sqlplus sys/123456@rac4 as sysdba  
17. SQL*Plus: Release 10.2.0.1.0 - Production on Sun Jan 29 13:26:19 2012  
18. Copyright (c) 1982, 2005, Oracle.  All rights reserved.  
19.  
20. Connected to:  
21. Oracle Database 10g Enterprise Edition Release 10.2.0.5.0 - 64bit Production  
22. With the Partitioning, Real Application Clusters, OLAP, Data Mining  
23. and Real Application Testing options  
24.  
25. SQL> col instance_name for a20  
26. SQL> col host_name for a40  
27. SQL> select instance_name,host_name from v$instance;  
28.  
29. INSTANCE_NAME        HOST_NAME  
30. -------------------- ----------------------------------------  
31. rac1                 rac1.yang.com  
32.  
33. SQL> conn sys/123456@rac4 as sysdba  
34. Connected.  
35. SQL> select instance_name,host_name from v$instance;  
36.  
37. INSTANCE_NAME        HOST_NAME  
38. -------------------- ----------------------------------------  
39. rac2                 rac2.yang.com  
40.  
41. [oracle@rac2 ~]$ srvctl stop instance -d rac -i rac2 -o immediate  
42. [oracle@rac2 ~]$ srvctl status database -d rac  
43. Instance rac1 is running on node rac1  
44. Instance rac2 is not running on node rac2  
45.  
46. [oracle@rhel6 ~]$ sqlplus sys/123456@rac4 as sysdba  
47. SQL*Plus: Release 10.2.0.1.0 - Production on Sun Jan 29 14:00:17 2012  
48. Copyright (c) 1982, 2005, Oracle.  All rights reserved.  
49.  
50. Connected to:  
51. Oracle Database 10g Enterprise Edition Release 10.2.0.5.0 - 64bit Production  
52. With the Partitioning, Real Application Clusters, OLAP, Data Mining  
53. and Real Application Testing options  
54.  
55. SQL> col instance_name for a20  
56. SQL> col host_name for a40  
57. SQL> select instance_name,host_name from v$instance;  
58.  
59. INSTANCE_NAME        HOST_NAME  
60. -------------------- ----------------------------------------  
61. rac1                 rac1.yang.com  
62.  
63. SQL> conn sys/123456@rac4 as sysdba  
64. Connected.  
65. SQL> select instance_name,host_name from v$instance;  
66.  
67. INSTANCE_NAME        HOST_NAME  
68. -------------------- ----------------------------------------  
69. rac1                 rac1.yang.com  
70.  
71. SQL> conn sys/123456@rac4 as sysdba  
72. Connected.  
73. SQL> select instance_name,host_name from v$instance;  
74.  
75. INSTANCE_NAME        HOST_NAME  
76. -------------------- ----------------------------------------  
77. rac1                 rac1.yang.com 

2: RAC环境下客户端的taf，10g的rac

1. [oracle@rhel6 ~]$ cd $ORACLE_HOME/network/admin  
2. [oracle@rhel6 admin]$ tail -17 tnsnames.ora   
3. RAC =  
4.   (DESCRIPTION =  
5.     (ADDRESS_LIST =  
6.       (ADDRESS = (PROTOCOL = TCP)(HOST = rac1-vip.yang.com)(PORT = 1521))  
7.       (ADDRESS = (PROTOCOL = TCP)(HOST = rac2-vip.yang.com)(PORT = 1521))  
8.     )  
9.     (LOAD_BALANCE=YES)  
10.     (FAILOVER=YES)  
11.     (CONNECT_DATA =  
12.       (SERVICE_NAME = rac.yang.com)  
13.       (FAILOVER_MODE =  
14.        (TYPE = SELECT)  
15.        (METHOD = BASIC)  
16.        (RETRIES = 180)  
17.        (DELAY = 5))  
18.     )  
19.   )  
20.  
21. [oracle@rhel6 admin]$ sqlplus sys/123456@rac as sysdba  
22. SQL*Plus: Release 10.2.0.1.0 - Production on Mon Jan 30 19:14:50 2012  
23. Copyright (c) 1982, 2005, Oracle.  All rights reserved.  
24.  
25. Connected to:  
26. Oracle Database 10g Enterprise Edition Release 10.2.0.5.0 - 64bit Production  
27. With the Partitioning, Real Application Clusters, OLAP, Data Mining  
28. and Real Application Testing options  
29.  
30. SQL> SELECT SID FROM V$MYSTAT WHERE ROWNUM=1;  
31.  
32.        SID  
33. ----------  
34.        148  
35.  
36. SQL> SELECT MACHINE, FAILOVER_TYPE, FAILOVER_METHOD, FAILED_OVER FROM V$SESSION WHERE SID=148;  
37.  
38. MACHINE              TYPE       METHOD      FAI  
39. -------------------- ---------- ----------- ---  
40. rhel6.yang.com       SELECT     BASIC       NO  
41.  
42. SQL> select instance_name from v$instance;  
43.  
44. INSTANCE_NAME  
45. ----------------  
46. rac1  
47.  
48. SQL> select * from dba_source; //构造长查询  
49.  
50. [oracle@rac1 ~]$ sqlplus /nolog  
51. SQL*Plus: Release 10.2.0.5.0 - Production on Mon Jan 30 19:20:18 2012  
52. Copyright (c) 1982, 2010, Oracle.  All Rights Reserved.  
53.  
54. SQL> conn /as sysdba  
55. Connected.  
56. SQL> select instance_name from v$instance;  
57.  
58. INSTANCE_NAME  
59. ------------------------------------------------  
60. rac1  
61.  
62. SQL> shutdown abort  
63. ORACLE instance shut down.  
64.  
65. [oracle@rac1 ~]$ srvctl status database -d rac  
66. Instance rac2 is running on node rac2  
67. Instance rac1 is not running on node rac1  
68.  
69.  
70. 前面的长查询将会继续，可以看到会话的sid已经改变，连接到了节点2上  
71. 295528 rows selected.  
72.  
73. SQL> SELECT SID FROM V$MYSTAT WHERE ROWNUM=1;  
74.  
75.        SID  
76. ----------  
77.        130  
78.  
79. SQL> SELECT MACHINE, FAILOVER_TYPE, FAILOVER_METHOD, FAILED_OVER FROM V$SESSION WHERE SID=130;  
80.  
81. MACHINE              TYPE       METHOD      FAI  
82. -------------------- ---------- ----------- ---  
83. rhel6.yang.com       SELECT     BASIC       YES  
84.  
85. SQL> select instance_name from v$instance;  
86.  
87. INSTANCE_NAME  
88. ----------------  
89. rac2 

3: RAC环境下客户端的taf，11g的rac，11g的rac提供了scan地址的功能，大赞！

1. [oracle@rhel6 admin]$ tail -14 tnsnames.ora   
2. NODE =  
3.   (DESCRIPTION =  
4.     (ADDRESS_LIST =  
5.       (ADDRESS = (PROTOCOL = TCP)(HOST = rac-scan.yang.com)(PORT = 1521))  
6.     )  
7.     (CONNECT_DATA =  
8.       (SERVICE_NAME = rac.yang.com)  
9.       (FAILOVER_MODE =  
10.        (TYPE = SELECT)  
11.        (METHOD = BASIC)  
12.        (RETRIES = 180)  
13.        (DELAY = 5))  
14.     )  
15.   )  
16.  
17. [oracle@rhel6 admin]$ sqlplus sys/Ab123456@node as sysdba  
18. SQL*Plus: Release 10.2.0.1.0 - Production on Mon Jan 30 20:41:00 2012  
19. Copyright (c) 1982, 2005, Oracle.  All rights reserved.  
20. Connected to:  
21. Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - 64bit Production  
22. With the Partitioning, Real Application Clusters, Automatic Storage Management, OLAP,  
23. Data Mining and Real Application Testing options  
24.  
25. SQL> select instance_name from v$instance;  
26.  
27. INSTANCE_NAME  
28. ----------------  
29. node2  
30.  
31. SQL> select sid from v$mystat where rownum=1;  
32.  
33.        SID  
34. ----------  
35.        141  
36.  
37. SQL> SELECT MACHINE, FAILOVER_TYPE, FAILOVER_METHOD, FAILED_OVER FROM V$SESSION WHERE SID=141;  
38.  
39. MACHINE              TYPE       METHOD      FAI  
40. -------------------- ---------- ----------- ---  
41. rhel6.yang.com       SELECT     BASIC       NO  
42.  
43. SQL> create table taf_test(id number,name varchar(20));  
44. Table created.  
45.  
46. SQL> insert into taf_test values (1,'zhangsan');  
47. 1 row created.  
48.  
49. SQL> update taf_test set id=2 where id=1;  
50. 1 row updated. 

这个时候不提交，使用shutdown abort命令关闭节点2，会话将自动连接到节点1上，但需要输入rollback命令回滚事务，否则不能执行正常的操作！

1. SQL> select * from taf_test;  
2.  
3.         ID NAME  
4. ---------- ---------------  
5.          2 zhangsan  
6.  
7. [oracle@node2 ~]$ srvctl stop instance -d rac -i node2 -o abort  
8. [oracle@node2 ~]$ srvctl status database -d rac  
9. Instance node1 is running on node node1  
10. Instance node2 is not running on node node2  
11.  
12. SQL> select * from dual;  
13. select * from dual  
14. *  
15. ERROR at line 1:  
16. ORA-25402: transaction must roll back  
17.  
18. SQL> rollback;  
19. Rollback complete.  
20.  
21. SQL> select instance_name from v$instance;  
22.  
23. INSTANCE_NAME  
24. ----------------  
25. node1 

4：服务器端的taf，在我的测试中配置失败，详情http://www.itpub.net/thread-1568414-1-1.html

2012年05月19日更新,http://t.askmaclean.com/viewthread.php?tid=1052&pid=5532&page=1&extra=page%3D1#pid5532

[oracle@rac2 ~]$ cat $TNS_ADMIN/listener.ora LISTENER_RAC2 =   (DESCRIPTION_LIST =     (DESCRIPTION =       (ADDRESS = (PROTOCOL = TCP)(HOST = rac2-vip.yang.com)(PORT = 1521)(IP = FIRST))       (ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.1.42)(PORT = 1521)(IP = FIRST))     )   ) SID_LIST_LISTENER_RAC2 =   (SID_LIST =     (SID_DESC =       (SID_NAME = PLSExtProc)       (ORACLE_HOME = /u01/app/oracle/product/10.2.0/db_1)       (PROGRAM = extproc)     )   ) [oracle@rac2 ~]$ cat $TNS_ADMIN/tnsnames.ora LISTENER_RAC2 =   (DESCRIPTION =     (ADDRESS_LIST =       (ADDRESS = (PROTOCOL = TCP)(HOST = rac2-vip.yang.com)(PORT = 1521))     )   ) LISTENER_RAC1 =   (DESCRIPTION =     (ADDRESS_LIST =       (ADDRESS = (PROTOCOL = TCP)(HOST = rac1-vip.yang.com)(PORT = 1521))     )   ) LISTENERS_RAC =   (DESCRIPTION =     (ADDRESS_LIST =       (ADDRESS = (PROTOCOL = TCP)(HOST = rac2-vip.yang.com)(PORT = 1521))       (ADDRESS = (PROTOCOL = TCP)(HOST = rac1-vip.yang.com)(PORT = 1521))     )   ) RAC2 =   (DESCRIPTION =     (ADDRESS = (PROTOCOL = TCP)(HOST = rac2-vip.yang.com)(PORT = 1521))     (CONNECT_DATA =       (SERVER = DEDICATED)       (SERVICE_NAME = rac.yang.com)       (INSTANCE_NAME = rac2)     )   ) RAC1 =   (DESCRIPTION =     (ADDRESS = (PROTOCOL = TCP)(HOST = rac1-vip.yang.com)(PORT = 1521))     (CONNECT_DATA =       (SERVER = DEDICATED)       (SERVICE_NAME = rac.yang.com)       (INSTANCE_NAME = rac1)     )   ) [oracle@rac2 ~]$ sqlplus /nolog SQL*Plus: Release 10.2.0.5.0 - Production on Fri May 18 20:55:39 2012 Copyright (c) 1982, 2010, Oracle.  All Rights Reserved. SQL> conn /as sysdba Connected. SQL> select name from dba_services; NAME -------------------------------------------------------------------------------- SYS$BACKGROUND SYS$USERS seeddataXDB seeddata racXDB rac.yang.com 6 rows selected. SQL> alter system set local_listener=LISTENER_RAC2 sid='rac2'; System altered. SQL> alter system set local_listener=LISTENER_RAC1 sid='rac1'; System altered. SQL> alter system set remote_listener=LISTENERS_RAC; System altered. [oracle@rac2 ~]$ srvctl  add service -d rac -s taf -r rac1,rac2 -P basic [oracle@rac2 ~]$ srvctl config service -d rac -s taf taf PREF: rac1 rac2 AVAIL: [oracle@rac2 ~]$ srvctl  start service -d rac -s taf [oracle@rac2 ~]$ srvctl status service -d rac -s taf Service taf is running on instance(s) rac1, rac2 [oracle@rac2 ~]$ sqlplus /nolog SQL*Plus: Release 10.2.0.5.0 - Production on Fri May 18 21:11:35 2012 Copyright (c) 1982, 2010, Oracle.  All Rights Reserved. SQL> conn /as sysdba Connected. SQL> show parameter service; NAME                                 TYPE ------------------------------------ --------------------------------- VALUE ------------------------------ service_names                        string taf, rac.yang.com   1  begin   2    dbms_service.modify_service(service_name        => 'taf',   3                     goal                => DBMS_SERVICE.goal_throughput,   4                     aq_ha_notifications => TRUE,   5                     failover_method     => DBMS_SERVICE.failover_method_basic,   6                     failover_type       => DBMS_SERVICE.failover_type_select,   7                     failover_retries    => 180,   8                     failover_delay      => 5,   9                     clb_goal            => DBMS_SERVICE.clb_goal_long); 10* end; SQL> / PL/SQL procedure successfully completed. SQL> col name format a15   SQL> col failover_method format a11 heading 'METHOD' SQL> col failover_type format a10 heading 'TYPE' SQL> col failover_retries format 9999999 heading 'RETRIES' SQL> col goal format a10 SQL> col clb_goal format a8 SQL> col AQ_HA_NOTIFICATIONS format a5 heading 'AQNOT' SQL>  select name,service_id from dba_services where name='taf'; NAME            SERVICE_ID --------------- ---------- taf                 7 SQL> select name, failover_method, failover_type, failover_retries,goal, clb_goal,aq_ha_notifications  from dba_services where service_id = 7; NAME            METHOD      TYPE        RETRIES GOAL       CLB_GOAL AQNOT --------------- ----------- ---------- -------- ---------- -------- ----- taf        BASIC       SELECT          180 THROUGHPUT LONG     YES [oracle@rhel6 admin]$ tail -12 tnsnames.ora TAF =   (DESCRIPTION =     (ADDRESS_LIST =       (ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.1.141)(PORT = 1521))       (ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.1.142)(PORT = 1521))     )     (LOAD_BALANCE=YES)     (CONNECT_DATA =       (SERVICE_NAME = taf.yang.com)     )   ) [oracle@rhel6 admin]$ sqlplus sys/123456@taf as sysdba SQL*Plus: Release 10.2.0.1.0 - Production on Fri May 18 23:19:08 2012 Copyright (c) 1982, 2005, Oracle.  All rights reserved. Connected to: Oracle Database 10g Enterprise Edition Release 10.2.0.5.0 - 64bit Production With the Partitioning, Real Application Clusters, OLAP, Data Mining and Real Application Testing options SQL> select sid from v$mystat where rownum=1;        SID ----------        129 SQL> col machine for a20 SQL> SELECT MACHINE, FAILOVER_TYPE, FAILOVER_METHOD, FAILED_OVER FROM V$SESSION WHERE SID=129; MACHINE              TYPE       METHOD      FAI -------------------- ---------- ----------- --- rhel6.yang.com       NONE       NONE        NO [oracle@rhel6 ~]$ sqlplus hr/hr@taf SQL*Plus: Release 10.2.0.1.0 - Production on Sat May 19 10:04:12 2012 Copyright (c) 1982, 2005, Oracle.  All rights reserved. Connected to: Oracle Database 10g Enterprise Edition Release 10.2.0.5.0 - 64bit Production With the Partitioning, Real Application Clusters, OLAP, Data Mining and Real Application Testing options SQL> select sid from v$mystat where rownum=1;        SID ----------        147 SQL> col machine for a20 SQL> SELECT MACHINE, FAILOVER_TYPE, FAILOVER_METHOD, FAILED_OVER FROM V$SESSION WHERE SID=147; MACHINE              TYPE       METHOD      FAI -------------------- ---------- ----------- --- rhel6.yang.com       SELECT     BASIC       NO 本文转自斩月博客51CTO博客，原文链接http://blog.51cto.com/ylw6006/769244如需转载请自行联系原作者 ylw6006