在Oracle 11g Data Guard中實現Connect Time Failover & Transparent Application Failover(TAF)

背景介紹：

在switchover或failover時主庫進行切換後，客戶端獲得自己重連主庫的能力。

環境修改：
1.修改$ORACLE_HOME/network/admin/tnsnames.ora

PRIOCM=
  (DESCRIPTION =
    (ADDRESS_LIST=
      (ADDRESS = (PROTOCOL = TCP)(HOST = ocm1.example.com)(PORT = 1521))  --主庫
      (ADDRESS = (PROTOCOL = TCP)(HOST = ocm2.example.com)(PORT = 1521))  --備庫
    )
    (CONNECT_DATA =
      (SERVICE_NAME = priocm)  --指定service名字
    )
  )

2.在主庫中創建並啓動service

begin
 dbms_service.create_service('priocm','priocm');  --service_name,network_name
end;
/
begin
 DBMS_SERVICE.START_SERVICE('priocm');
end;
/

3.在主庫中創建啓動觸發器，當database_role爲非主庫時關閉service

create or replace trigger priocmtrigg after startup on database
declare
 v_role varchar(30);
begin
 select database_role into v_role from v$database;
 if v_role = 'PRIMARY' then
 DBMS_SERVICE.START_SERVICE('priocm');
 else
 DBMS_SERVICE.STOP_SERVICE('priocm');
 end if;
end;
/

4.修改servicefailover參數

begin
 dbms_service.modify_service
 ('priocm',
 FAILOVER_METHOD => 'BASIC', --BASIC：是指在感知到節點故障時才創建到其他實例的連接。PRECONNECT: 是在最初建立連接時就同時建立到所有實例的連接，當發生故障時，立刻就可以切換到其他鏈路
 FAILOVER_TYPE => 'SELECT',  --session和select，這2種方式對於未提交的事務都會自動回滾，區別在於對select 語句的處理，對於select，用戶正在執行的select語句會被轉移到新的實例上，在新的節點上繼續返回後續結果集，而已經返回的記錄集則拋棄。
 FAILOVER_RETRIES => 200,    --重試次數
 FAILOVER_DELAY => 1);	     --重試間隔時間
end;
/

切換實驗：

模擬在客戶端通過service(priocm)連接

[oracle@ocm1 admin]$ sqlplus sys/oracle@priocm as sysdba

SQL*Plus: Release 11.2.0.3.0 Production on Sun Jun 25 16:07:33 2017

Copyright (c) 1982, 2011, Oracle.  All rights reserved.


Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options

SYS@priocm> select db_unique_name,name,database_role,switchover_status from v$database;  --連接到當前主庫

DB_UNIQUE_NAME		       NAME	 DATABASE_ROLE	  SWITCHOVER_STATUS
------------------------------ --------- ---------------- --------------------
aux			       PROD3	 PRIMARY	  TO STANDBY

----------------------------------------------------------------------------------------------------------------
省略switchover過程，http://blog.csdn.net/u013169075/article/details/73555409
----------------------------------------------------------------------------------------------------------------

switchover後，再次模擬在客戶端通過service(priocm)連接

SYS@priocm> /
select db_unique_name,name,database_role,switchover_status from v$database
*
ERROR at line 1:
ORA-03113: end-of-file on communication channel   --嘗試操作主庫拋出錯誤
Process ID: 4810
Session ID: 28 Serial number: 7


ERROR:
ORA-03114: not connected to ORACLE


SYS@priocm> exit
Disconnected from Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
--嘗試重連主庫
[oracle@ocm1 ~]$ sqlplus sys/oracle@priocm as sysdba

SQL*Plus: Release 11.2.0.3.0 Production on Sun Jun 25 16:49:45 2017

Copyright (c) 1982, 2011, Oracle.  All rights reserved.


Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options

SYS@priocm> select db_unique_name,name,database_role,switchover_status from v$database;  --已經連接到新主庫

DB_UNIQUE_NAME		       NAME	 DATABASE_ROLE	  SWITCHOVER_STATUS
------------------------------ --------- ---------------- --------------------
PROD3			       PROD3	 PRIMARY	  FAILED DESTINATION

參考資料：
http://www.oracle.com/technetwork/cn/articles/database-performance/oracle-rac-connection-mgmt-1650424-zhs.html
https://uhesse.com/2009/08/19/connect-time-failover-transparent-application-failover-for-data-guard/