mycat 主从读写分离-主存切换（验证）

转自：http://blog.csdn.net/mchdba/article/details/50616534

在前面主从实现文章基础上实现mycat读写分离

6，读写分离模式

6.1然后修改mycat的schema.xml：

balance为1：让全部的readHost及备用的writeHost参与select的负载均衡。 
switchType为2：基于MySQL主从同步的状态决定是否切换。 
heartbeat：主从切换的心跳语句必须为show slave status。 
 
有配置读节点： 
 

6.2 打开debug模式

[root@wgq_idc_squid_1_11 conf]# vim log4j.xml
value="info" /> 变成  value="debug" />

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6.3 执行查询读操作

在mycat窗口上执行select操作：

mysql> explain select * from company where id=1;
+-----------+----------------------------------------------+
| DATA_NODE | SQL                                          |
+-----------+----------------------------------------------+
| dn3       | SELECT * FROM company WHERE id = 1 LIMIT 100 |
+-----------+----------------------------------------------+
1 row in set (0.14 sec)

mysql> select * from company where id=1;
+----+---------+
| id | name    |
+----+---------+
|  1 | alibaba |
+----+---------+
1 row in set (0.01 sec)

mysql>

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后台日志显示出只在3327上执行：

01/18 01:35:01.536  DEBUG [$_NIOREACTOR-3-RW] (PhysicalDBPool.java:452) -select read source hostS2 for dataHost:wgq_idc_mon_1_11
01/18 01:35:01.537  DEBUG [$_NIOREACTOR-3-RW] (MySQLConnection.java:445) -con need syn ,total syn cmd 2 commands SET names latin1;SET SESSION TRANSACTION ISOLATION LEVEL REPEATABLE READ;schema change:false con:MySQLConnection [id=14, lastTime=1453052101537, user=root, schema=db1, old shema=db1, borrowed=true, fromSlaveDB=false, threadId=3326, charset=latin1, txIsolation=0, autocommit=true, attachment=dn1{SELECT *
FROM company
WHERE id = 1
LIMIT 100}, respHandler=SingleNodeHandler [node=dn1{SELECT *
FROM company
WHERE id = 1
LIMIT 100}, packetId=0], host=127.0.0.1, port=3327, statusSync=null, writeQueue=0, modifiedSQLExecuted=false]
01/18 01:35:01.546  DEBUG [$_NIOREACTOR-2-RW] (NonBlockingSession.java:229) -release connection MySQLConnection [id=14, lastTime=1453052101529, user=root, schema=db1, old shema=db1, borrowed=true, fromSlaveDB=false, threadId=3326, charset=latin1, txIsolation=3, autocommit=true, attachment=dn1{SELECT *
FROM company
WHERE id = 1
LIMIT 100}, respHandler=SingleNodeHandler [node=dn1{SELECT *
FROM company
WHERE id = 1
LIMIT 100}, packetId=5], host=127.0.0.1, port=3327, statusSync=org.opencloudb.mysql.nio.MySQLConnection$StatusSync@7fb43f0f, writeQueue=0, modifiedSQLExecuted=false]
01/18 01:35:01.547  DEBUG [$_NIOREACTOR-2-RW] (PhysicalDatasource.java:403) -release channel MySQLConnection [id=14, lastTime=1453052101529, user=root, schema=db1, old shema=db1, borrowed=true, fromSlaveDB=false, threadId=3326, charset=latin1, txIsolation=3, autocommit=true, attachment=null, respHandler=null, host=127.0.0.1, port=3327, statusSync=null, writeQueue=0, modifiedSQLExecuted=false]
^C

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6.4 执行写操作

Mycat窗口写操作： 

后台log显示写操作在3317上： 

01/18 01:39:54.550  DEBUG [$_NIOREACTOR-3-RW] (NonBlockingSession.java:229) -release connection MySQLConnection [id=7, lastTime=1453052394535, user=root, schema=db3, old shema=db3, borrowed=true, fromSlaveDB=false, threadId=163, charset=latin1, txIsolation=3, autocommit=true, attachment=dn3{insert into company values(3,'baidu')}, respHandler=org.opencloudb.mysql.nio.handler.MultiNodeQueryHandler@42bed1e7, host=127.0.0.1, port=3317, statusSync=null, writeQueue=0, modifiedSQLExecuted=true]
01/18 01:39:54.550  DEBUG [$_NIOREACTOR-3-RW] (PhysicalDatasource.java:403) -release channel MySQLConnection [id=7, lastTime=1453052394535, user=root, schema=db3, old shema=db3, borrowed=true, fromSlaveDB=false, threadId=163, charset=latin1, txIsolation=3, autocommit=true, attachment=null, respHandler=null, host=127.0.0.1, port=3317, statusSync=null, writeQueue=0, modifiedSQLExecuted=false]
01/18 01:39:54.550  DEBUG [$_NIOREACTOR-3-RW] (MultiNodeQueryHandler.java:171) -received ok response ,executeResponse:true from MySQLConnection [id=3, lastTime=1453052394535, user=root, schema=db2, old shema=db2, borrowed=true, fromSlaveDB=false, threadId=162, charset=latin1, txIsolation=3, autocommit=true, attachment=dn2{insert into company values(3,'baidu')}, respHandler=org.opencloudb.mysql.nio.handler.MultiNodeQueryHandler@42bed1e7, host=127.0.0.1, port=3317, statusSync=null, writeQueue=0, modifiedSQLExecuted=true]
01/18 01:39:54.551  DEBUG [$_NIOREACTOR-3-RW] (NonBlockingSession.java:229) -release connection MySQLConnection [id=3, lastTime=1453052394535, user=root, schema=db2, old shema=db2, borrowed=true, fromSlaveDB=false, threadId=162, charset=latin1, txIsolation=3, autocommit=true, attachment=dn2{insert into company values(3,'baidu')}, respHandler=org.opencloudb.mysql.nio.handler.MultiNodeQueryHandler@42bed1e7, host=127.0.0.1, port=3317, statusSync=null, writeQueue=0, modifiedSQLExecuted=true]
01/18 01:39:54.551  DEBUG [$_NIOREACTOR-3-RW] (PhysicalDatasource.java:403) -release channel MySQLConnection [id=3, lastTime=1453052394535, user=root, schema=db2, old shema=db2, borrowed=true, fromSlaveDB=false, threadId=162, charset=latin1, txIsolation=3, autocommit=true, attachment=null, respHandler=null, host=127.0.0.1, port=3317, statusSync=null, writeQueue=0, modifiedSQLExecuted=false]

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Check下主从数据是否都已经写入了： 
主库3317端口： 

从裤3327端口： 

---

7，主从切换测试

7.1 mycat托管配置如下

     <dataHost name="wgq_idc_mon_1_11" maxCon="1000" minCon="10" balance="1"
                writeType="0" dbType="mysql" dbDriver="native" switchType="2"  slaveThreshold="100">
                <heartbeat>show slave statusheartbeat>
                
                <writeHost host="hostM1" url="127.0.0.1:3317" user="root" password="">
                        <readHost host="hostR1" url="127.0.0.1:3327" user="root" password=""/>
                writeHost>
                <writeHost host="hostS2" url="127.0.0.1:3327" user="root" password="" />
        dataHost>

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7.2 关闭主库，写操作切换到从裤3327端口

关闭主库 

[root@wgq_idc_squid_1_11 conf]# service mysql56m1 stop
Shutting down MySQL....                                    [确定]
[root@wgq_idc_squid_1_11 conf]#

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Mycat后台报错：

01/18 01:50:01.037   INFO [Timer0] (PhysicalDatasource.java:373) -not ilde connection in pool,create new connection for hostM1 of schema db1
01/18 01:50:01.038   INFO [$_NIOConnector] (AbstractConnection.java:458) -close connection,reason:java.net.ConnectException: 拒绝连接 ,MySQLConnection [id=0, lastTime=1453053001035, user=root, schema=db1, old shema=db1, borrowed=false, fromSlaveDB=false, threadId=0, charset=utf8, txIsolation=0, autocommit=true, attachment=null, respHandler=null, host=127.0.0.1, port=3317, statusSync=null, writeQueue=0, modifiedSQLExecuted=false]
01/18 01:50:01.038   INFO [$_NIOConnector] (SQLJob.java:111) -can't get connection for sql :show slave status
01/18 01:50:01.038   WARN [$_NIOREACTOR-1-RW] (MySQLDetector.java:139) -found MySQL master/slave Replication err !!! DBHostConfig [hostName=hostR1, url=127.0.0.1:3327]error reconnecting to master 'repl@127.0.0.1:3317' - retry-time: 60  retries: 1
0

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看到主从失效，因为主down了。

因为我们通过mycat配置了主从切换模式，现在3317端口主库down了，那么写库应该自动切换到从裤3327上面，如果在mycat上面写入，就应该写到3327端口的从库了，验证如下： 
（1）在mycat窗口录入数据： 
 
（2）在3327端口从裤验证数据： 

看到3327端口的数据有新录入的4,meituan的数据。表明验证成功。 
(3) dnindex属性文件中writeHost已经变成了第二个了，如下所示： 

7.3 再启动原来的主库3317端口，在mycat上做写操作，后台mysql写库还是原来的从库3327端口：

这个时候就会报错，主从连接失败，原因是从库3327会再重新从主库3317同步所有的数据，但是从库已经有了，所以就会报错，如下所示： 

我采用

stop slave;
 set global sql_slave_skip_counter=1;
 start slave;
 show slave status\G;

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一个个忽略过后，就正常了，没有报错： 

但是这个时候如果再在mycat窗口上录入数据，debug分析面，还是会写入到3327里面去： 

后台debug日志： 

OK，至此，mycat主从切换成功。

补充点：实际生产环境需要配置双主，不会切到读库