今天测试了MySQL的高可用架构--MHA，并进行了自动切换、手动failover以及手动在线切换，其中手动在线切换发现小坑：当旧master切换为新slave后，没有自动将read_only设置为on，例证如下：
环境说明：
OS：CentOS release 6.5
MySQL: 5.6.22-71.0-log Percona Server
slave1：172.16.52.130
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mysql> show variables like ‘read_only‘; +---------------+-------+ | Variable_name | Value | +---------------+-------+ | read_only | ON | +---------------+------- |
slave2：172.16.52.132
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mysql> show variables like ‘read_only‘; +---------------+-------+ | Variable_name | Value | +---------------+-------+ | read_only | ON | +---------------+-------+ |
master:172.16.52.131
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mysql> show variables like ‘read_only‘; +---------------+-------+ | Variable_name | Value | +---------------+-------+ | read_only | OFF | +---------------+-------+ |
在MHA-manager上进行手动在线切换：
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masterha_master_switch --conf=/etc/masterha/app1.cnf --master_state=alive --orig_master_is_new_slave --interactive=0 &>/masterha/app1/manager.log 部分信息： [info] Switching master to 172.16.52.130(172.16.52.130:3306) completed successfully. |
可以发现172.16.52.130切位主库（可以指定新主库：--new_master_host=IP,--new_master_port=PORT）
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mysql> show slave hosts; +-----------+------+------+-----------+--------------------------------------+ | Server_id | Host | Port | Master_id | Slave_UUID | +-----------+------+------+-----------+--------------------------------------+ | 132 | | 3306 | 130 | e173b5bf-e286-11e4-8d56-000c29c78a39 | | 131 | | 3306 | 130 | 18f4bdc7-e285-11e4-8d4a-000c298dfc24 | +-----------+------+------+-----------+--------------------------------------+ |
查看原主库-新从库的参数：172.16.52.131
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mysql> show variables like ‘read_only‘; +---------------+-------+ | Variable_name | Value | +---------------+-------+ | read_only | OFF | +---------------+-------+ |
slave 2:172.16.52.132
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mysql> show variables like ‘read_only‘; +---------------+-------+ | Variable_name | Value | +---------------+-------+ | read_only | ON | +---------------+-------+ |
master:172.16.52.130
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mysql> show variables like ‘read_only‘; +---------------+-------+ | Variable_name | Value | +---------------+-------+ | read_only | OFF | +---------------+-------+ |
总结：
发现从库切换为主库，关闭read_only，主库切换为从库，为打开read_only，所以切换完后，需要手动修改新的从库参数
set global read_only=on;