Oracle的RAC的高可用功能除了负载均衡还包括TAF（Transparent Application Failover）。

RAC的TAF是指会话连接到一个实例上，如果这个实例出现了故障，Oracle会自动将会话迁移到另一个实例上。

RAC的TAF简单测试（一）：http://yangtingkun.itpub.net/post/468/283068

RAC的TAF简单测试（二）：http://yangtingkun.itpub.net/post/468/283277

RAC的TAF简单测试（三）：http://yangtingkun.itpub.net/post/468/283474

RAC的TAF简单测试（四）：http://yangtingkun.itpub.net/post/468/284898

这篇简单讨论一下TAF服务器端的PRECONNECT设置。

上一篇讨论了客户端配置PRECONNECT方式的TAF，下面介绍一下RAC服务器端设置PRECONNECT服务的方法：

通过图形界面启动dbca；

在欢迎界面选择Oracle Real Application Cluster database；

选择Service Management；

选择CLUSTER数据库，这里是testrac；

在Database Service界面添加要启动的服务：PRE_TESTRAC，然后将TAF策略修改为Pre-connect，点击Finish，完成配置。

这是服务器端的tnsnames.ora中添加了下面的配置：

PRE_TESTRAC =
(DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP)(HOST = racnode1-vip)(PORT = 1521))
(ADDRESS = (PROTOCOL = TCP)(HOST = racnode2-vip)(PORT = 1521))
(LOAD_BALANCE = yes)
(CONNECT_DATA =
(SERVER = DEDICATED)
(SERVICE_NAME = PRE_TESTRAC)
(FAILOVER_MODE =
(BACKUP = PRE_TESTRAC_PRECONNECT)
(TYPE = SELECT)
(METHOD = PRECONNECT)
(RETRIES = 180)
(DELAY = 5)
)
)
)

PRE_TESTRAC_PRECONNECT =
(DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP)(HOST = racnode1-vip)(PORT = 1521))
(ADDRESS = (PROTOCOL = TCP)(HOST = racnode2-vip)(PORT = 1521))
(LOAD_BALANCE = yes)
(CONNECT_DATA =
(SERVER = DEDICATED)
(SERVICE_NAME = PRE_TESTRAC_PRECONNECT)
(FAILOVER_MODE =
(BACKUP = PRE_TESTRAC)
(TYPE = SELECT)
(METHOD = BASIC)
(RETRIES = 180)
(DELAY = 5)
)
)
)

同时，通过srvctl可以监控、管理建立的PER_TESTRAC服务：

bash-2.03$ srvctl status service -d testrac
Service PRE_TESTRAC is running on instance(s) testrac2, testrac1

建立了服务之后，客户端可以直接配置PRE_TESTRAC这个服务，比如客户端tnsnames.ora的配置为：

PRE_TESTRAC_SERVICE =
(DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP)(HOST = 172.25.198.224)(PORT = 1521))
(ADDRESS = (PROTOCOL = TCP)(HOST = 172.25.198.225)(PORT = 1521))
(LOAD_BALANCE = yes)
(CONNECT_DATA =
(SERVER = DEDICATED)
(SERVICE_NAME = PRE_TESTRAC)
(FAILOVER_MODE =
(TYPE = SELECT)
(METHOD = PRECONNECT)
(BACKUP = PRE_TESTRAC_PRECONNECT)
)
)
)

通过服务名PRE_TESTRAC_SERVICE建立的连接就启用了PRECONNECT的TAF：

SQL> CONN TEST/TEST@PRE_TESTRAC_SERVICE已连接。
SQL> SELECT SID, FAILOVER_TYPE, FAILOVER_METHOD, FAILED_OVER
2 FROM V$SESSION
3 WHERE SID IN (SELECT SID FROM V$MYSTAT WHERE ROWNUM = 1);

SID FAILOVER_TYPE FAILOVER_M FAI
---------- ------------- ---------- ---
127 SELECT PRECONNECT NO