写一份mycat双主双从server.xml的配置文件

以下是一个简单的MyCat双主双从的server.xml配置文件示例：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mycat:server SYSTEM "server.dtd">
<mycat:server xmlns:mycat="http://io.mycat/">
    <system>
        <property name="user">mycat</property>
        <property name="password">mycat</property>
        <property name="useSqlStat">true</property>
        <property name="useGlobleTableCheck">false</property>
    </system>
    <user name="mycat">
        <property name="password">mycat</property>
        <property name="schemas">db1,db2,db3</property>
    </user>
    <dataHost name="master1" maxCon="1000" minCon="10" balance="0" writeType="0" dbType="mysql" dbDriver="native" switchType="1" slaveThreshold="100">
        <heartbeat>select user()</heartbeat>
        <writeHost host="127.0.0.1" url="jdbc:mysql://127.0.0.1:3306/db1" user="root" password="root">
            <readHost host="127.0.0.1" url="jdbc:mysql://127.0.0.1:3306/db1" user="root" password="root" />
        </writeHost>
        <writeHost host="127.0.0.1" url="jdbc:mysql://127.0.0.1:3306/db2" user="root" password="root">
            <readHost host="127.0.0.1" url="jdbc:mysql://127.0.0.1:3306/db2" user="root" password="root" />
        </writeHost>
    </dataHost>
    <dataHost name="master2" maxCon="1000" minCon="10" balance="0" writeType="0" dbType="mysql" dbDriver="native" switchType="1" slaveThreshold="100">
        <heartbeat>select user()</heartbeat>
        <writeHost host="127.0.0.1" url="jdbc:mysql://127.0.0.1:3306/db3" user="root" password="root">
            <readHost host="127.0.0.1" url="jdbc:mysql://127.0.0.1:3306/db3" user="root" password="root" />
        </writeHost>
        <writeHost host="127.0.0.1" url="jdbc:mysql://127.0.0.1:3306/db4" user="root" password="root">
            <readHost host="127.0.0.1" url="jdbc:mysql://127.0.0.1:3306/db4" user="root" password="root" />
        </writeHost>
    </dataHost>
    <dataNode name="dn1" dataHost="master1" database="db1" />
    <dataNode name="dn2" dataHost="master1" database="db2" />
    <dataNode name="dn3" dataHost="master2" database="db3" />
    <dataNode name="dn4" dataHost="master2" database="db4" />
    <tableRule name="rule1">
        <rule>
            <columns>id</columns>
            <algorithm>hash</algorithm>
        </rule>
        <dataSource name="ds1">
            <rule>
                <table name="table1" dataNode="dn1,dn2" />
                <table name="table2" dataNode="dn1,dn2" />
            </rule>
        </dataSource>
        <dataSource name="ds2">
            <rule>
                <table name="table3" dataNode="dn3,dn4" />
                <table name="table4" dataNode="dn3,dn4" />
            </rule>
        </dataSource>
    </tableRule>
</mycat:server>

这个文件定义了两个数据主机（master1和master2），每个主机都有两个写主机和两个读主机。每个数据主机有两个数据节点（dn1，dn2，dn3，dn4），每个数据节点对应一个具体的数据库。最后，还定义了一个名为“rule1”的表规则，将不同的数据表分配到不同的数据源中。