配置 RAC 负载均衡与故障转移
2015-01-07 17:00
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Oracle负载均衡主要是指新会话连接到RAC数据库时,如何判定这个新的连接要连到哪个节点进行工作?通常情况下，负载均衡分为客户端负载
均衡与服务器端负载均衡。客户端负载均衡通常是在客户端的tnsnames.ora中多添加一个链接地址以及LOAD_BALANCE与failover参数。而服务器
端的负载均衡则相对复杂，下面具体描述服务器端负载均衡。
一、负载均衡
注意这里的负载均衡指的是连接的负载均衡，即客户可以随机从不同的实例中连接到数据库
1.配置tnsnames.ora使得该文件中包含如下全部内容：
[sql]
view plaincopyprint?
# LISTENERS_DEVDB DEVDB是数据库名，可以使用netmgr,netca编辑或直接使用Vim创建
LISTENERS_DEVDB =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = rac1-vip.robinson.com)(PORT = 1521))
(ADDRESS = (PROTOCOL = TCP)(HOST = rac2-vip.robinson.com)(PORT = 1521))
)
2.配置参数文件remote_listener
[sql]
view plaincopyprint?
SQL> alter system set remote_listener='LISTENERS_DEVDB' scope=both sid='*';
3.需要配置连接描述信息的两个IP地址、端口号、以及load_balance子项为yes (主要是load_balance子项)
[sql]
view plaincopyprint?
DEVDB =
(DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP)(HOST = rac1-vip.robinson.com)(PORT = 1521))
(ADDRESS = (PROTOCOL = TCP)(HOST = rac2-vip.robinson.com)(PORT = 1521))
(LOAD_BALANCE = yes)
(CONNECT_DATA =
(SERVER = DEDICATED)
(SERVICE_NAME = devdb.robinson.com)
)
)
4.查看侦听器的状态，从下面可以看到devdb.robinson.com服务中有两个实例为其提供服务
[sql]
view plaincopyprint?
[oracle@rac2 ~]$ lsnrctl status
Service "devdb.robinson.com" has 2 instance(s).
Instance "devdb1", status READY, has 1 handler(s) for this service...
Instance "devdb2", status READY, has 2 handler(s) for this service...
5.测试负载均衡
使用shell脚本来进行测试负载均衡
[sql]
view plaincopyprint?
--编辑TestLoadBalance.sh
#!/bin/bash
#Usage: TestLoadBalance devdb 1000
count=0
while [ $count -lt $2 ] # Set up a loop control
do # Begin the loop
count='expr $count + 1' # Increment the counter
sqlplus -s usr1/usr1pwd@$1 @TestLoadBalance.sql # Connect instance and execute sql statement
sleep 1
done
--TestLoadBalance.sql 脚本
col instance_name format a30
select instance_name from v$instance;
--实施测试
./TestLoadBalance.sh devdb 1000
--查看结果
SQL> select inst_id,count(1) from gv$instance group by inst_d;
INST_ID COUNT(1)
---------- ----------
devdb1 446
devdb2 554
二、配置故障转移
负载均衡是用于实现基于连接的负载均衡，但不能解决节点是否可用，一旦一个节点损坏，已成功连接的客户端并不能转移到其他正常服务的
实例中。而故障转移功能则使得该功能得以实现。可以使用srvctl 和dbca来创建服务。下面使用dbca来创建一个新的服务，客户端连接到实
例后，对故障实现透明切换。
1.配置故障转移服务
在节点rac1使用oracle帐户启动dbca工具，
a.选择 Oracle Real Application Clusters database
b.选择 Services Management
c.集群数据库列表：单击 Next。
d.数据库服务：单击 Add。
添加服务：输入sales。
选择 devdb1 作为首选实例。
选择 devdb2 作为可用实例。
TAF 策略：选择 Basic。
单击 Finish。
e.数据库配置助手：单击 No 退出。
配置完毕后，在tnsnames.ora中多出了以下内容，注意是各个节点都会多出以下内容
[sql]
view plaincopyprint?
SALES =
(DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP)(HOST = rac1-vip.robinson.com)(PORT = 1521))
(ADDRESS = (PROTOCOL = TCP)(HOST = rac2-vip.robinson.com)(PORT = 1521))
(LOAD_BALANCE = yes)
(CONNECT_DATA =
(SERVER = DEDICATED)
(SERVICE_NAME = sales.robinson.com)
(FAILOVER = --failover_mode是实现故障转移的关键选项
(TYPE = SELECT)
(METHOD = BASIC) --TAF 策略：此处当前为 Basic
(RETRIES = 180)
(DELAY = 5)
)
)
)
同时参数service_names会多出一个服务名，位于在配置数据库服务时选择的首选实例中
[sql]
view plaincopyprint?
SQL> select instance_name from v$instance;
INSTANCE_NAME
----------------
devdb1
SQL> show parameter service_names
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
service_names string devdb.robinson.com, sales
SQL> select instance_name from v$instance;
INSTANCE_NAME
----------------
devdb2
SQL> show parameter service
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
service_names string devdb.robinson.com
使用srvctl工具也可以看到该服务已经正常开始提供服务
[sql]
view plaincopyprint?
SQL> ho srvctl status service -d devdb -s sales
Service sales is running on instance(s) devdb1
SQL> ho lsnrctl status
Service "sales.robinson.com" has 1 instance(s). --sales正常提供服务
Instance "devdb1", status READY, has 2 handler(s) for this service...
2.实现故障转移
下面使用帐户usr1，服务名sales从Windows客户端来登陆，注意要配置好客户端tnsnames，可以将服务器sales项内容全部复制到客户端tnsnames.ora中
[sql]
view plaincopyprint?
C:\>sqlplus usr1/usr1@sales
SQL> col host_name format a20
SQL> select instance_number ins_no,instance_name,host_name,status from v$instance;
INS_NO INSTANCE_NAME HOST_NAME STATUS
---------- ---------------- -------------------- ------------
1 devdb1 rac1.robinson.com OPEN
SQL> select failover_type,failover_method,failed_over from v$session
2 where username='USR1';
FAILOVER_TYPE FAILOVER_M FAI
------------- ---------- ---
SELECT BASIC NO
--从其它会话使用sys帐户登陆到crm 并关闭该实例
SQL> show user;
USER is "SYS"
SQL> select instance_name from v$instance;
INSTANCE_NAME
----------------
devdb1
SQL> shutdown abort
ORACLE instance shut down.
--从先前登陆到sales的会话中验证会话故障切换功能
SQL> select instance_number ins_no,instance_name,host_name,status from v$instance;
INS_NO INSTANCE_NAME HOST_NAME STATUS
---------- ---------------- -------------------- ------------
2 devdb2 rac2.robinson.com OPEN
SQL> select failover_type,failover_method,failed_over from v$session
2 where username='USR1'; --第3列显示的为yes，也表明经过故障切换后提供的服务
FAILOVER_TYPE FAILOVER_M FAI
------------- ---------- ---
SELECT BASIC YES
--由下面的查询中可以看到服务名sales被添加到可用实例devdb2，节点rac2 的service_names参数中
SQL> select instance_name from v$instance;
INSTANCE_NAME
----------------
devdb2
SQL> show parameter service
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
service_names string devdb.robinson.com, sales
3.重新定位故障转移服务到首选实例
对于首选实例从故障中恢复后，需要手动来重新定位到首选实例
[sql]
view plaincopyprint?
SQL> startup --启动devdb1
SQL> show parameter service_names
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
service_names string devdb.robinson.com
SQL> ho srvctl relocate service -d devdb -s sales -i devdb2 -t devdb1
SQL> show parameter service_names
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
service_names string devdb.robinson.com, sales
4.DML故障转移(不同于DQL，因此单独列出)
使用Windows客户端通过sales服务名登陆
[sql]
view plaincopyprint?
C:\>sqlplus usr1/usr1@sales
SQL> show user;
USER is "USR1"
SQL> create table tb_temp (id int,ename varchar2(20)) tablespace tbs1;
Table created.
SQL> insert into tb_temp
2 select 1,'Robinson' from dual
3 union all
4 select 2,'Jackson' from dual;
2 rows created.
SQL> commit;
Commit complete.
SQL> select * from tb_temp;
ID ENAME
---------- --------------------
1 Robinson
2 Jackson
SQL> delete from tb_temp;
2 rows deleted.
SQL> select * from tb_temp;
no rows selected
从另一个会话中使用sysdba关闭devdb1(shutdown abort)
再在刚刚执行表创建的会话中查询记录，收到提示，事务必须被回滚
[sql]
view plaincopyprint?
SQL> select * from tb_temp;
select * from tb_temp
*
ERROR at line 1:
ORA-25402: transaction must roll back
SQL> rollback;
Rollback complete.
SQL> select * from tb_temp;
ID ENAME
---------- --------------------
1 Robinson
2 Jackson
SQL> select failover_type,failover_method,failed_over from v$session
2 where username='USR1';
FAILOVER_TYPE FAILOVER_M FAI
------------- ---------- ---
SELECT BASIC YES
总结：对于DML 操作在实现故障转移时，将严格按照ACID原则来执行，大部分情况需要回滚事务。
此文转自：http://blog.csdn.net/leshami/article/details/6791667
Oracle负载均衡主要是指新会话连接到RAC数据库时,如何判定这个新的连接要连到哪个节点进行工作?通常情况下，负载均衡分为客户端负载
均衡与服务器端负载均衡。客户端负载均衡通常是在客户端的tnsnames.ora中多添加一个链接地址以及LOAD_BALANCE与failover参数。而服务器
端的负载均衡则相对复杂，下面具体描述服务器端负载均衡。
一、负载均衡
注意这里的负载均衡指的是连接的负载均衡，即客户可以随机从不同的实例中连接到数据库
1.配置tnsnames.ora使得该文件中包含如下全部内容：
[sql]
view plaincopyprint?
# LISTENERS_DEVDB DEVDB是数据库名，可以使用netmgr,netca编辑或直接使用Vim创建
LISTENERS_DEVDB =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = rac1-vip.robinson.com)(PORT = 1521))
(ADDRESS = (PROTOCOL = TCP)(HOST = rac2-vip.robinson.com)(PORT = 1521))
)
# LISTENERS_DEVDB DEVDB是数据库名，可以使用netmgr,netca编辑或直接使用Vim创建 LISTENERS_DEVDB = (ADDRESS_LIST = (ADDRESS = (PROTOCOL = TCP)(HOST = rac1-vip.robinson.com)(PORT = 1521)) (ADDRESS = (PROTOCOL = TCP)(HOST = rac2-vip.robinson.com)(PORT = 1521)) )
2.配置参数文件remote_listener
[sql]
view plaincopyprint?
SQL> alter system set remote_listener='LISTENERS_DEVDB' scope=both sid='*';
SQL> alter system set remote_listener='LISTENERS_DEVDB' scope=both sid='*';
3.需要配置连接描述信息的两个IP地址、端口号、以及load_balance子项为yes (主要是load_balance子项)
[sql]
view plaincopyprint?
DEVDB =
(DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP)(HOST = rac1-vip.robinson.com)(PORT = 1521))
(ADDRESS = (PROTOCOL = TCP)(HOST = rac2-vip.robinson.com)(PORT = 1521))
(LOAD_BALANCE = yes)
(CONNECT_DATA =
(SERVER = DEDICATED)
(SERVICE_NAME = devdb.robinson.com)
)
)
DEVDB = (DESCRIPTION = (ADDRESS = (PROTOCOL = TCP)(HOST = rac1-vip.robinson.com)(PORT = 1521)) (ADDRESS = (PROTOCOL = TCP)(HOST = rac2-vip.robinson.com)(PORT = 1521)) (LOAD_BALANCE = yes) (CONNECT_DATA = (SERVER = DEDICATED) (SERVICE_NAME = devdb.robinson.com) ) )
4.查看侦听器的状态，从下面可以看到devdb.robinson.com服务中有两个实例为其提供服务
[sql]
view plaincopyprint?
[oracle@rac2 ~]$ lsnrctl status
Service "devdb.robinson.com" has 2 instance(s).
Instance "devdb1", status READY, has 1 handler(s) for this service...
Instance "devdb2", status READY, has 2 handler(s) for this service...
[oracle@rac2 ~]$ lsnrctl status Service "devdb.robinson.com" has 2 instance(s). Instance "devdb1", status READY, has 1 handler(s) for this service... Instance "devdb2", status READY, has 2 handler(s) for this service...
5.测试负载均衡
使用shell脚本来进行测试负载均衡
[sql]
view plaincopyprint?
--编辑TestLoadBalance.sh
#!/bin/bash
#Usage: TestLoadBalance devdb 1000
count=0
while [ $count -lt $2 ] # Set up a loop control
do # Begin the loop
count='expr $count + 1' # Increment the counter
sqlplus -s usr1/usr1pwd@$1 @TestLoadBalance.sql # Connect instance and execute sql statement
sleep 1
done
--TestLoadBalance.sql 脚本
col instance_name format a30
select instance_name from v$instance;
--实施测试
./TestLoadBalance.sh devdb 1000
--查看结果
SQL> select inst_id,count(1) from gv$instance group by inst_d;
INST_ID COUNT(1)
---------- ----------
devdb1 446
devdb2 554
--编辑TestLoadBalance.sh #!/bin/bash #Usage: TestLoadBalance devdb 1000 count=0 while [ $count -lt $2 ] # Set up a loop control do # Begin the loop count='expr $count + 1' # Increment the counter sqlplus -s usr1/usr1pwd@$1 @TestLoadBalance.sql # Connect instance and execute sql statement sleep 1 done --TestLoadBalance.sql 脚本 col instance_name format a30 select instance_name from v$instance; --实施测试 ./TestLoadBalance.sh devdb 1000 --查看结果 SQL> select inst_id,count(1) from gv$instance group by inst_d; INST_ID COUNT(1) ---------- ---------- devdb1 446 devdb2 554
二、配置故障转移
负载均衡是用于实现基于连接的负载均衡，但不能解决节点是否可用，一旦一个节点损坏，已成功连接的客户端并不能转移到其他正常服务的
实例中。而故障转移功能则使得该功能得以实现。可以使用srvctl 和dbca来创建服务。下面使用dbca来创建一个新的服务，客户端连接到实
例后，对故障实现透明切换。
1.配置故障转移服务
在节点rac1使用oracle帐户启动dbca工具，
a.选择 Oracle Real Application Clusters database
b.选择 Services Management
c.集群数据库列表：单击 Next。
d.数据库服务：单击 Add。
添加服务：输入sales。
选择 devdb1 作为首选实例。
选择 devdb2 作为可用实例。
TAF 策略：选择 Basic。
单击 Finish。
e.数据库配置助手：单击 No 退出。
配置完毕后，在tnsnames.ora中多出了以下内容，注意是各个节点都会多出以下内容
[sql]
view plaincopyprint?
SALES =
(DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP)(HOST = rac1-vip.robinson.com)(PORT = 1521))
(ADDRESS = (PROTOCOL = TCP)(HOST = rac2-vip.robinson.com)(PORT = 1521))
(LOAD_BALANCE = yes)
(CONNECT_DATA =
(SERVER = DEDICATED)
(SERVICE_NAME = sales.robinson.com)
(FAILOVER = --failover_mode是实现故障转移的关键选项
(TYPE = SELECT)
(METHOD = BASIC) --TAF 策略：此处当前为 Basic
(RETRIES = 180)
(DELAY = 5)
)
)
)
SALES = (DESCRIPTION = (ADDRESS = (PROTOCOL = TCP)(HOST = rac1-vip.robinson.com)(PORT = 1521)) (ADDRESS = (PROTOCOL = TCP)(HOST = rac2-vip.robinson.com)(PORT = 1521)) (LOAD_BALANCE = yes) (CONNECT_DATA = (SERVER = DEDICATED) (SERVICE_NAME = sales.robinson.com) (FAILOVER = --failover_mode是实现故障转移的关键选项 (TYPE = SELECT) (METHOD = BASIC) --TAF 策略：此处当前为 Basic (RETRIES = 180) (DELAY = 5) ) ) )
同时参数service_names会多出一个服务名，位于在配置数据库服务时选择的首选实例中
[sql]
view plaincopyprint?
SQL> select instance_name from v$instance;
INSTANCE_NAME
----------------
devdb1
SQL> show parameter service_names
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
service_names string devdb.robinson.com, sales
SQL> select instance_name from v$instance;
INSTANCE_NAME
----------------
devdb2
SQL> show parameter service
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
service_names string devdb.robinson.com
SQL> select instance_name from v$instance; INSTANCE_NAME ---------------- devdb1 SQL> show parameter service_names NAME TYPE VALUE ------------------------------------ ----------- ------------------------------ service_names string devdb.robinson.com, sales SQL> select instance_name from v$instance; INSTANCE_NAME ---------------- devdb2 SQL> show parameter service NAME TYPE VALUE ------------------------------------ ----------- ------------------------------ service_names string devdb.robinson.com
使用srvctl工具也可以看到该服务已经正常开始提供服务
[sql]
view plaincopyprint?
SQL> ho srvctl status service -d devdb -s sales
Service sales is running on instance(s) devdb1
SQL> ho lsnrctl status
Service "sales.robinson.com" has 1 instance(s). --sales正常提供服务
Instance "devdb1", status READY, has 2 handler(s) for this service...
SQL> ho srvctl status service -d devdb -s sales Service sales is running on instance(s) devdb1 SQL> ho lsnrctl status Service "sales.robinson.com" has 1 instance(s). --sales正常提供服务 Instance "devdb1", status READY, has 2 handler(s) for this service...
2.实现故障转移
下面使用帐户usr1，服务名sales从Windows客户端来登陆，注意要配置好客户端tnsnames，可以将服务器sales项内容全部复制到客户端tnsnames.ora中
[sql]
view plaincopyprint?
C:\>sqlplus usr1/usr1@sales
SQL> col host_name format a20
SQL> select instance_number ins_no,instance_name,host_name,status from v$instance;
INS_NO INSTANCE_NAME HOST_NAME STATUS
---------- ---------------- -------------------- ------------
1 devdb1 rac1.robinson.com OPEN
SQL> select failover_type,failover_method,failed_over from v$session
2 where username='USR1';
FAILOVER_TYPE FAILOVER_M FAI
------------- ---------- ---
SELECT BASIC NO
--从其它会话使用sys帐户登陆到crm 并关闭该实例
SQL> show user;
USER is "SYS"
SQL> select instance_name from v$instance;
INSTANCE_NAME
----------------
devdb1
SQL> shutdown abort
ORACLE instance shut down.
--从先前登陆到sales的会话中验证会话故障切换功能
SQL> select instance_number ins_no,instance_name,host_name,status from v$instance;
INS_NO INSTANCE_NAME HOST_NAME STATUS
---------- ---------------- -------------------- ------------
2 devdb2 rac2.robinson.com OPEN
SQL> select failover_type,failover_method,failed_over from v$session
2 where username='USR1'; --第3列显示的为yes，也表明经过故障切换后提供的服务
FAILOVER_TYPE FAILOVER_M FAI
------------- ---------- ---
SELECT BASIC YES
--由下面的查询中可以看到服务名sales被添加到可用实例devdb2，节点rac2 的service_names参数中
SQL> select instance_name from v$instance;
INSTANCE_NAME
----------------
devdb2
SQL> show parameter service
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
service_names string devdb.robinson.com, sales
C:\>sqlplus usr1/usr1@sales SQL> col host_name format a20 SQL> select instance_number ins_no,instance_name,host_name,status from v$instance; INS_NO INSTANCE_NAME HOST_NAME STATUS ---------- ---------------- -------------------- ------------ 1 devdb1 rac1.robinson.com OPEN SQL> select failover_type,failover_method,failed_over from v$session 2 where username='USR1'; FAILOVER_TYPE FAILOVER_M FAI ------------- ---------- --- SELECT BASIC NO --从其它会话使用sys帐户登陆到crm 并关闭该实例 SQL> show user; USER is "SYS" SQL> select instance_name from v$instance; INSTANCE_NAME ---------------- devdb1 SQL> shutdown abort ORACLE instance shut down. --从先前登陆到sales的会话中验证会话故障切换功能 SQL> select instance_number ins_no,instance_name,host_name,status from v$instance; INS_NO INSTANCE_NAME HOST_NAME STATUS ---------- ---------------- -------------------- ------------ 2 devdb2 rac2.robinson.com OPEN SQL> select failover_type,failover_method,failed_over from v$session 2 where username='USR1'; --第3列显示的为yes，也表明经过故障切换后提供的服务 FAILOVER_TYPE FAILOVER_M FAI ------------- ---------- --- SELECT BASIC YES --由下面的查询中可以看到服务名sales被添加到可用实例devdb2，节点rac2 的service_names参数中 SQL> select instance_name from v$instance; INSTANCE_NAME ---------------- devdb2 SQL> show parameter service NAME TYPE VALUE ------------------------------------ ----------- ------------------------------ service_names string devdb.robinson.com, sales
3.重新定位故障转移服务到首选实例
对于首选实例从故障中恢复后，需要手动来重新定位到首选实例
[sql]
view plaincopyprint?
SQL> startup --启动devdb1
SQL> show parameter service_names
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
service_names string devdb.robinson.com
SQL> ho srvctl relocate service -d devdb -s sales -i devdb2 -t devdb1
SQL> show parameter service_names
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
service_names string devdb.robinson.com, sales
SQL> startup --启动devdb1 SQL> show parameter service_names NAME TYPE VALUE ------------------------------------ ----------- ------------------------------ service_names string devdb.robinson.com SQL> ho srvctl relocate service -d devdb -s sales -i devdb2 -t devdb1 SQL> show parameter service_names NAME TYPE VALUE ------------------------------------ ----------- ------------------------------ service_names string devdb.robinson.com, sales
4.DML故障转移(不同于DQL，因此单独列出)
使用Windows客户端通过sales服务名登陆
[sql]
view plaincopyprint?
C:\>sqlplus usr1/usr1@sales
SQL> show user;
USER is "USR1"
SQL> create table tb_temp (id int,ename varchar2(20)) tablespace tbs1;
Table created.
SQL> insert into tb_temp
2 select 1,'Robinson' from dual
3 union all
4 select 2,'Jackson' from dual;
2 rows created.
SQL> commit;
Commit complete.
SQL> select * from tb_temp;
ID ENAME
---------- --------------------
1 Robinson
2 Jackson
SQL> delete from tb_temp;
2 rows deleted.
SQL> select * from tb_temp;
no rows selected
C:\>sqlplus usr1/usr1@sales SQL> show user; USER is "USR1" SQL> create table tb_temp (id int,ename varchar2(20)) tablespace tbs1; Table created. SQL> insert into tb_temp 2 select 1,'Robinson' from dual 3 union all 4 select 2,'Jackson' from dual; 2 rows created. SQL> commit; Commit complete. SQL> select * from tb_temp; ID ENAME ---------- -------------------- 1 Robinson 2 Jackson SQL> delete from tb_temp; 2 rows deleted. SQL> select * from tb_temp; no rows selected
从另一个会话中使用sysdba关闭devdb1(shutdown abort)
再在刚刚执行表创建的会话中查询记录，收到提示，事务必须被回滚
[sql]
view plaincopyprint?
SQL> select * from tb_temp;
select * from tb_temp
*
ERROR at line 1:
ORA-25402: transaction must roll back
SQL> rollback;
Rollback complete.
SQL> select * from tb_temp;
ID ENAME
---------- --------------------
1 Robinson
2 Jackson
SQL> select failover_type,failover_method,failed_over from v$session
2 where username='USR1';
FAILOVER_TYPE FAILOVER_M FAI
------------- ---------- ---
SELECT BASIC YES
SQL> select * from tb_temp; select * from tb_temp * ERROR at line 1: ORA-25402: transaction must roll back SQL> rollback; Rollback complete. SQL> select * from tb_temp; ID ENAME ---------- -------------------- 1 Robinson 2 Jackson SQL> select failover_type,failover_method,failed_over from v$session 2 where username='USR1'; FAILOVER_TYPE FAILOVER_M FAI ------------- ---------- --- SELECT BASIC YES
总结：对于DML 操作在实现故障转移时，将严格按照ACID原则来执行，大部分情况需要回滚事务。
此文转自：http://blog.csdn.net/leshami/article/details/6791667
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