TAF（Transparent Application Failover）即透明應用程式故障轉移技術。當初始化連線出現問題無法連線時，該功能可以保證應用程式重新連線到可用服務。在重新連線過程中，之前的活動事務將會被回滾，但在“具體條件”下TAF可以保證SELECT語句不被終止。這也是RAC亮點之一。

本文給出使用Oracle RAC的TAF技術實現不間斷查詢。

1.在tnsnames.ora檔案中新增測試連線串
RACDB1@rac1 /home/oracle$ vi $ORACLE_HOME/network/admin/tnsnames.ora
testractaf =
(DESCRIPTION =
    (ADDRESS = (PROTOCOL = TCP)(HOST = rac1-vip)(PORT = 1521))
    (ADDRESS = (PROTOCOL = TCP)(HOST = rac2-vip)(PORT = 1521))
    (LOAD_BALANCE = yes)
    (CONNECT_DATA =
      (SERVER = DEDICATED)
      (SERVICE_NAME = RACDB)
      (FAILOVER_MODE =
        (TYPE = SELECT)
        (METHOD = BASIC)
        (RETRIES = 180)
        (DELAY = 5)
      )
    )
)

所謂的“具體條件”指的就是FAILOVER_MODE中METHOD選擇“BASIC”、TYPE選擇“SELECT”。

2.使用testractaf連線串連線到資料庫
RACDB1@rac1 /home/oracle$ sqlplus sec/sec@testractaf

SQL*Plus: Release 10.2.0.1.0 - Production on Sun Oct 24 19:21:35 2010

Copyright (c) 1982, 2005, Oracle. All rights reserved.

Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Production
With the Partitioning, Real Application Clusters, OLAP and Data Mining options

SQL> select instance_name from v$instance;

INSTANCE_NAME
----------------
RACDB1

可見，此時sqlplus連線到了RAC的第一個例項RACDB1上。

3.手工停止RACDB1例項
[root@rac2 ~]# srvctl stop instance -d RACDB -i RACDB1

4.重新確認查詢語句所在例項
SQL> select instance_name from v$instance;

INSTANCE_NAME
----------------
RACDB2

注意觀察，此時的查詢語句沒有報出任何錯誤。結果表明，此時sqlplus已經順利的連線到了RAC的第二個例項RACDB2上。

5.恢復例項RACDB1，繼續
[root@rac2 ~]# srvctl start instance -d RACDB -i RACDB1
SQL> select instance_name from v$instance;

INSTANCE_NAME
----------------
RACDB2

6.此處我們模擬一個長時間無法返回全部資訊的查詢語句
SQL> select * from all_objects a,all_objects b,all_objects c where a.object_id=b.object_id and a.object_id=c.object_id;

…… 此處省略輸出資訊 ……

7.手工停止RACDB2例項
[root@rac2 ~]# crs_stat -t
Name           Type           Target    State     Host
------------------------------------------------------------
ora....B1.inst application    ONLINE    ONLINE    rac1
ora....B2.inst application    ONLINE    ONLINE    rac2
ora.RACDB.db   application    ONLINE    ONLINE    rac2
ora....DB1.srv application    ONLINE    ONLINE    rac1
ora....DB2.srv application    ONLINE    ONLINE    rac2
ora.....taf.cs application    ONLINE    ONLINE    rac1
ora....SM1.asm application    ONLINE    ONLINE    rac1
ora....C1.lsnr application    ONLINE    ONLINE    rac1
ora.rac1.gsd   application    ONLINE    ONLINE    rac1
ora.rac1.ons   application    ONLINE    ONLINE    rac1
ora.rac1.vip   application    ONLINE    ONLINE    rac1
ora....SM2.asm application    ONLINE    ONLINE    rac2
ora....C2.lsnr application    ONLINE    ONLINE    rac2
ora.rac2.gsd   application    ONLINE    ONLINE    rac2
ora.rac2.ons   application    ONLINE    ONLINE    rac2
ora.rac2.vip   application    ONLINE    ONLINE    rac2
[root@rac2 ~]# srvctl stop instance -d RACDB -i RACDB2
[root@rac2 ~]# crs_stat -t
Name           Type           Target    State     Host
------------------------------------------------------------
ora....B1.inst application    ONLINE    ONLINE    rac1
ora....B2.inst application    OFFLINE   OFFLINE
ora.RACDB.db   application    ONLINE    ONLINE    rac2
ora....DB1.srv application    ONLINE    ONLINE    rac1
ora....DB2.srv application    ONLINE    OFFLINE
ora.....taf.cs application    ONLINE    ONLINE    rac1
ora....SM1.asm application    ONLINE    ONLINE    rac1
ora....C1.lsnr application    ONLINE    ONLINE    rac1
ora.rac1.gsd   application    ONLINE    ONLINE    rac1
ora.rac1.ons   application    ONLINE    ONLINE    rac1
ora.rac1.vip   application    ONLINE    ONLINE    rac1
ora....SM2.asm application    ONLINE    ONLINE    rac2
ora....C2.lsnr application    ONLINE    ONLINE    rac2
ora.rac2.gsd   application    ONLINE    ONLINE    rac2
ora.rac2.ons   application    ONLINE    ONLINE    rac2
ora.rac2.vip   application    ONLINE    ONLINE    rac2

8.結論
注意觀察sqlplus視窗中不間斷的結果輸出，在RACDB2例項中斷過程中，可以看到輸出結果在短暫的停頓後重新恢復輸出，沒有報錯。這便是TAF帶給我們的技術特性。
在手工“Ctrl + C”取消螢幕輸出後可以觀察到此時sqlplus已經連線到RACDB1例項。
SQL> select instance_name from v$instance;

INSTANCE_NAME
----------------
RACDB1

9.小結
本文給出了在FAILOVER_MODE中METHOD選擇“BASIC”、TYPE選擇“SELECT”時，使用Oracle的TAF技術在RAC環境下實現SELECT語句不間斷輸出的例子。在實際應用中可以考慮使用該技術，保證查詢語句不因例項故障而中斷。

Good luck.

secooler
10.10.24

-- The End --

【TAF】使用Oracle RAC的TAF技術實現不間斷查詢

相關文章