Mycat实现MySQL的分库分表、读写分离、主从切换

最近主要投入在平安云MySQL DRDS的项目中，本人主要负责zookeeper模块的配置及后台脚本的编写。为了加深对DRDS整体架构的认识，我觉得有必要手工搭建基于Mycat实现的Mysql分布式数据库集群，现和大家分享下搭建流程，后续会针对Mycat的各项配置作进一步研究，敬请期待。
Mycat及MySQL实例部署情况：
Mycat：
IP：10.20.8.57，Port：3310/3311
MySQL ：
db1-M1，IP：10.20.8.126，Port：3306
db1-M2，IP：10.20.8.126，Port：3307
db2-M1，IP：10.25.80.7，Port：3307
架构图如下：

配置Mycat
server.xml：

<!DOCTYPE mycat:server SYSTEM "server.dtd">
<mycat:server xmlns:mycat="http://io.mycat/">
    <system>
        <property name="useSqlStat">1</property>
        <property name="useGlobleTableCheck">0</property>
        <property name="defaultSqlParser">druidparser</property>
        <property name="sequnceHandlerType">2</property>
        <property name="processorBufferPoolType">0</property>
        <property name="serverPort">3310</property>      <!-- mycat的使用端口 -->
        <property name="managerPort">3311</property>      <!-- mycat的管理端口 -->
        <property name="handleDistributedTransactions">0</property>
        <property name="useOffHeapForMerge">1</property>
        <property name="memoryPageSize">1m</property>
        <property name="spillsFileBufferSize">1k</property>
        <property name="useStreamOutput">0</property>
        <property name="systemReserveMemorySize">389m</property>
    </system>
    <user name="root">
        <property name="password">123456</property>
        <property name="schemas">db</property>
        <property name="readOnly">false</property>
    </user>
</mycat:server>

schema.xml：

<?xml version="1.0"?>
<!DOCTYPE mycat:schema SYSTEM "schema.dtd">
<mycat:schema xmlns:mycat="http://io.mycat/">

    <!-- 数据库配置，与server.xml中的数据库对应 -->
    <schema name="db" checkSQLschema="false" sqlMaxLimit="100">                     
        <table name="t1"  dataNode="dn1,dn2"  rule="mod-long" />       <!-- 对2取模，详见rule.xml -->
    </schema>

    <!-- 分片配置 -->
    <dataNode name="dn1" dataHost="shard1" database="db1" />                        
    <dataNode name="dn2" dataHost="shard2" database="db2" />

    <!-- 物理数据库配置 -->
    <dataHost name="shard1" maxCon="1000" minCon="10" balance="3"  writeType="0" dbType="mysql" dbDriver="native" switchType="1" slaveThreshold="100">
        <heartbeat>select user();</heartbeat>
        <writeHost host="db1-M1" url="10.20.8.126:3306" user="root" password="123456">  
                <readHost host="db1-M2" url="10.20.8.126:3307" user="root" password="123456" />
        </writeHost>

        <!-- 配置standby writeHost -->
        <writeHost host="db1-M2" url="10.20.8.126:3307" user="root" password="123456">  
        </writeHost> 

    </dataHost>

    <dataHost name="shard2" maxCon="1000" minCon="10" balance="0" writeType="0" dbType="mysql" dbDriver="native" switchType="1" slaveThreshold="100">
        <heartbeat>select user();</heartbeat>
        <writeHost host="db2-M1" url="10.25.80.7:3307" user="root" password="123456">  
        </writeHost>
    </dataHost>

</mycat:schema>

修改rule.xml中下列配置项：

<tableRule name="mod-long">
        <rule>
            <columns>id</columns>           <!-- t1的分片列 -->
            <algorithm>mod-long</algorithm>
        </rule>
</tableRule>

<function name="mod-long" class="io.mycat.route.function.PartitionByMod">
        <!-- how many data nodes -->
        <property name="count">2</property> <!-- count值与分片个数相同 -->
</function>

配置文件中各标签的含义可参考文章：MyCat关键配置说明

启动Mycat:

[root@SZB-L0059021 bin]# ./mycat start
Starting Mycat-server...
[root@SZB-L0059021 bin]# ./mycat status
Mycat-server is running (27020).
[root@SZB-L0059021 bin]# mysql -uroot -p123456 -Ddb -h127.0.0.1 -P3310

分库分表验证：

mysql> show tables;
+--------------+
| Tables in db |
+--------------+
| t1           |
+--------------+
1 row in set (0.00 sec)
mysql> desc t1;
+---------+-------------+------+-----+---------+-------+
| Field   | Type        | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| id      | int(11)     | YES  |     | NULL    |       |
| db_name | varchar(20) | YES  |     | NULL    |       |
+---------+-------------+------+-----+---------+-------+
2 rows in set (0.01 sec)
mysql> insert into t1(id,db_name) values(1,database());    
Query OK, 1 row affected (0.01 sec)
mysql> insert into t1(id,db_name) values(2,database());      
Query OK, 1 row affected (0.03 sec)
mysql> select * from t1;   
+------+---------+
| id   | db_name |
+------+---------+
|    2 | db1     |    --id=2，对2取模为0，所以插入dn1         
|    1 | db2     |    --id=1，对2取模为1，所以插入dn2 
+------+---------+ 
2 rows in set (0.01 sec)
上述查询结果可知，两次插入的数据分落入了db1、db2上，实现了分库

读写分离验证：

mysql> select * from t1;   
+------+---------+
| id   | db_name |
+------+---------+
|    2 | db1     |     --来自shard1上的db1-M2     
|    1 | db2     |     --来自shard2上的db2-M1
+------+---------+
2 rows in set (0.01 sec)

查看日志可知，上述查询结果来自dn1中db1-M2（端口3307）和dn2中的db2-M1：
2018-05-08 15:03:39.385 DEBUG [$_NIOREACTOR-0-RW] (io.mycat.server.NonBlockingSession.execute(NonBlockingSession.java:110)) - ServerConnection [id=1, schema=db, host=127.0.0.1, user=root,txIsolation=3, autocommit=true, schema=db]select * from t1, route={
   1 -> dn1{SELECT *
FROM t1
LIMIT 100}
   2 -> dn2{SELECT *
FROM t1
LIMIT 100}
}
...
2018-05-08 15:03:39.391 DEBUG [$_NIOREACTOR-0-RW] (io.mycat.backend.mysql.nio.handler.MultiNodeQueryHandler.rowEofResponse(MultiNodeQueryHandler.java:311)) - on row end reseponse MySQLConnection [id=29, lastTime=1525763019368, user=root, schema=db1, old shema=db1, borrowed=true, fromSlaveDB=true, threadId=511, charset=utf8, txIsolation=3, autocommit=true, attachment=dn1{SELECT *
FROM t1
LIMIT 100}, respHandler=io.mycat.backend.mysql.nio.handler.MultiNodeQueryHandler@66328ec4, host=10.20.8.126, port=3307, statusSync=null, writeQueue=0, modifiedSQLExecuted=false]
...
2018-05-08 15:03:39.392 DEBUG [$_NIOREACTOR-0-RW] (io.mycat.backend.mysql.nio.handler.MultiNodeQueryHandler.rowEofResponse(MultiNodeQueryHandler.java:311)) - on row end reseponse MySQLConnection [id=3, lastTime=1525763019387, user=root, schema=db2, old shema=db2, borrowed=true, fromSlaveDB=false, threadId=28, charset=utf8, txIsolation=3, autocommit=true, attachment=dn2{SELECT *
FROM t1
LIMIT 100}, respHandler=io.mycat.backend.mysql.nio.handler.MultiNodeQueryHandler@66328ec4, host=10.25.80.7, port=3307, statusSync=null, writeQueue=0, modifiedSQLExecuted=false]
...

主从切换：
通过查看mycat/conf目录下的dnindex.properties文件，可以知道mycat正在使用的writeHost，0表示schema.xml中dataHost标签下的第一个writeHost。

[root@SZB-L0059021 conf]# cat dnindex.properties 
#update
#Tue May 08 12:59:24 CST 2018
shard2=0
shard1=0               --此时状态正常，mycat选取每个dataHost标签中的第一个writeHost作为写入入口

切换至10.20.8.126主机，并手动停掉db1-M1

10.20.8.126:3306:Master > mysqladmin -uroot -p123456 shutdown

回到10.20.8.57（mycat主机），再次查看dnindex.properties

[root@SZB-L0059021 conf]# cat dnindex.properties 
#update
#Tue May 08 15:12:12 CST 2018
shard2=0
shard1=1              --db1-M1被shutdown后，mycat在shard1上的writeHost切换至db1-M2

切换至10.20.8.57（mycat所在主机），执行下述insert命令

mysql> insert into t1(id,db_name) values(4,database());           
Query OK, 1 row affected (0.01 sec)

查看日志可知，Mycat此时选择通过db1-M2（端口3307）写入数据：
2018-05-08 15:13:44.987 DEBUG [$_NIOREACTOR-0-RW] (io.mycat.server.NonBlockingSession.releaseConnection(NonBlockingSession.java:341)) - release connection MySQLConnection [id=24, lastTime=1525763624968, user=root, schema=db1, old shema=db1, borrowed=true, fromSlaveDB=false, threadId=506, charset=utf8, txIsolation=3, autocommit=true, attachment=dn1{insert into t1(id,db_name) values(4,database())}, respHandler=SingleNodeHandler [node=dn1{insert into t1(id,db_name) values(4,database())}, packetId=1], host=10.20.8.126, port=3307, statusSync=null, writeQueue=0, modifiedSQLExecuted=true]

由于dataHost中配置了writeType="0"，所以即使db1-M1重启恢复后，Mycat仍然会选择db1-M2作为shard1的
writeHost。
验证：

切换至10.20.8.126主机，并手动启动db1-M1
10.20.8.126:3306:Master > mysqld_safe &

在Mycat中插入验证数据
mysql> insert into t1(id,db_name) values(6,database());
Query OK, 1 row affected (0.02 sec)
查看日志可知，数据仍通过db1-M2（端口3307）写入：
2018-05-08 15:16:09.579 DEBUG [$_NIOREACTOR-0-RW] (io.mycat.server.NonBlockingSession.releaseConnection(NonBlockingSession.java:341)) - release connection MySQLConnection [id=32, lastTime=1525763769548, user=root, schema=db1, old shema=db1, borrowed=true, fromSlaveDB=false, threadId=514, charset=utf8, txIsolation=3, autocommit=true, attachment=dn1{insert into t1(id,db_name) values(6,database())}, respHandler=SingleNodeHandler [node=dn1{insert into t1(id,db_name) values(6,database())}, packetId=1], host=10.20.8.126, port=3307, statusSync=null, writeQueue=0, modifiedSQLExecuted=true]

此时要想让Mycat在shard1上的writeHost重新变为db1-M1，只需修改dnindex.properties中的shard1=1为shard1=0，并重启Mycat即可。