RAC負載均衡的簡單測試（一）

Rac環境安裝完成之後，打算簡單測試一下Oracle RAC的負載均衡功能。

配置負載均衡，需要在客戶端的tnsnames.ora中進行配置。

TESTRAC =
(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 = testrac)
)
)

設定了LOAD_BALANCE = yes之後，使用TESTRAC服務名連線資料庫時就啟動了負載均衡功能。

登陸RAC例項，檢查兩個例項上的會話連線情況：

SQL> SELECT INST_ID, COUNT(*) FROM GV$SESSION GROUP BY INST_ID;

INST_ID COUNT(*)
---------- ----------
1 31
2 31

下面在客戶端連線RAC例項，並檢查當前連線的是哪個例項：

SQL> CONN NDMAIN@TESTRAC輸入口令: ******已連線。
SQL> SELECT INSTANCE_NAME FROM V$INSTANCE;

INSTANCE_NAME
----------------
testrac1

SQL> CONN NDMAIN@TESTRAC輸入口令: ******已連線。
SQL> SELECT INSTANCE_NAME FROM V$INSTANCE;

INSTANCE_NAME
----------------
testrac2

由於兩個例項上會話數量相當，所以Oracle在分配連線時，分配給每個例項的機率基本相同。

這是會話連線兩次的情況，下面看看當多個會話連線時，Oracle是如何分配的。

SQL> DISC從 Oracle Database 10g Enterprise Edition Release 10.2.0.2.0 - 64bit Production
With the Partitioning, Real Application Clusters, OLAP and Data Mining options 斷開

首先斷開剛才連線的會話，然後啟動4個新的連線，並檢查這些連線分佈到哪些例項上：

E:>SQLPLUS NDMAIN/NDMAIN@TESTRAC

SQL*Plus: Release 10.2.0.1.0 - Production on 星期四 3月 22 19:15:26 2007

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

連線到:
Oracle Database 10g Enterprise Edition Release 10.2.0.2.0 - 64bit Production
With the Partitioning, Real Application Clusters, OLAP and Data Mining options

SQL> SELECT INSTANCE_NAME FROM V$INSTANCE;

INSTANCE_NAME
----------------
testrac1

SQL> HOST
Microsoft Windows 2000 [Version 5.00.2195]
(C) 版權所有 1985-2000 Microsoft Corp.

E:>SQLPLUS NDMAIN/NDMAIN@TESTRAC

SQL*Plus: Release 10.2.0.1.0 - Production on 星期四 3月 22 19:15:46 2007

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

連線到:
Oracle Database 10g Enterprise Edition Release 10.2.0.2.0 - 64bit Production
With the Partitioning, Real Application Clusters, OLAP and Data Mining options

SQL> SELECT INSTANCE_NAME FROM V$INSTANCE;

INSTANCE_NAME
----------------
testrac1

SQL> HOST
Microsoft Windows 2000 [Version 5.00.2195]
(C) 版權所有 1985-2000 Microsoft Corp.

E:>SQLPLUS NDMAIN/NDMAIN@TESTRAC

SQL*Plus: Release 10.2.0.1.0 - Production on 星期四 3月 22 19:16:02 2007

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

連線到:
Oracle Database 10g Enterprise Edition Release 10.2.0.2.0 - 64bit Production
With the Partitioning, Real Application Clusters, OLAP and Data Mining options

SQL> SELECT INSTANCE_NAME FROM V$INSTANCE;

INSTANCE_NAME
----------------
testrac2

SQL> HOST
Microsoft Windows 2000 [Version 5.00.2195]
(C) 版權所有 1985-2000 Microsoft Corp.

E:>SQLPLUS NDMAIN/NDMAIN@TESTRAC

SQL*Plus: Release 10.2.0.1.0 - Production on 星期四 3月 22 19:16:16 2007

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

連線到:
Oracle Database 10g Enterprise Edition Release 10.2.0.2.0 - 64bit Production
With the Partitioning, Real Application Clusters, OLAP and Data Mining options

SQL> SELECT INSTANCE_NAME FROM V$INSTANCE;

INSTANCE_NAME
----------------
testrac2

可以看到，由於兩個例項負載相當，Oracle基本上是按照50%的機率給每個例項分配新的連線。