我们来学习读写分离与负载均衡
先看一下balance 属性

负载均衡类型，目前的取值有3种：
1. balance="0",不开启读写分离机制，所有读操作都发送到当前可用的writeHost上。

2. balance="1"，全部的readHost与stand by writeHost参与select语句的负载均衡，简单的说，当双主双从模式(M1->S1，M2->S2，并且M1与M2互为主备)，正常情况下，M2,S1,S2都参与select语句的负载均衡。

3. balance="2"，所有读操作都随机的在writeHost、readhost上分发。

4. balance="3"，所有读请求随机的分发到wiriterHost对应的readhost执行，writerHost不负担读压力，注意balance=3只在1.4及其以后版本有，1.3没有。

writeType属性

负载均衡类型，目前的取值有3种：

1.writeType="0",所有写操作发送到配置的第一个writeHost，第一个挂了切到还生存的第二个writeHost，重新启动后已切换后的为准，切换记录在配置文件中:dnindex.properties.

2.writeType="1"，所有写操作都随机的发送到配置的writeHost。

3.writeType="2"，没实现。

<dataNode name="dn1" dataHost="localhost1" database="examdb" />

<dataNode name="dn2" dataHost="localhost2" database="examdb" />

<dataNode name="dn3" dataHost="localhost3" database="examdb" />

<dataHost name="localhost1" maxCon="1000" minCon="10" balance="2"

writeType="0" dbType="mysql" dbDriver="native" switchType="1" slaveThreshold="100">

<heartbeat>select user()</heartbeat>

<!-- can have multi write hosts -->

<writeHost host="hostM1" url="192.168.6.121:3306" user="root"

password="ESBecs00">

<!-- can have multi read hosts -->

</writeHost>

<writeHost host="hostS1" url="192.168.6.121:3307" user="root"

password="ESBecs00">

<!-- can have multi read hosts -->

</writeHost>

</dataHost>

<dataHost name="localhost2" maxCon="1000" minCon="10" balance="2"

writeType="0" dbType="mysql" dbDriver="native" switchType="1" slaveThreshold="100">

<heartbeat>select user()</heartbeat>

<!-- can have multi write hosts -->

<writeHost host="hostM1" url="192.168.6.120:3306" user="root"

password="ESBecs00">

<!-- can have multi read hosts -->

</writeHost>

<writeHost host="hostS1" url="192.168.6.120:3307" user="root"

password="ESBecs00">

<!-- can have multi read hosts -->

</writeHost>

</dataHost>

<dataHost name="localhost3" maxCon="1000" minCon="10" balance="2"

writeType="0" dbType="mysql" dbDriver="native" switchType="1" slaveThreshold="100">

<heartbeat>select user()</heartbeat>

<!-- can have multi write hosts -->

<writeHost host="hostM1" url="192.168.6.119:3306" user="root"

password="ESBecs00">

<!-- can have multi read hosts -->

</writeHost>

<writeHost host="hostM1" url="192.168.6.119:3307" user="root"

password="ESBecs00">

<!-- can have multi read hosts -->

</writeHost>

</dataHost>

#!/usr/bin/bash
for((i=1;i<=1000;i++))
do
mysql -uroot -p123456 -P8066 -h227.0.0.1 -e "select name from company" TESTDB;
done


root@localhost logs]# sort test-blance.log |more |uniq -c

30 this is 119
17 this is 119:3307
28 this is 120
23 this is 120:3307
36 this is 121
26 this is 121:3307