Mysql主从方式的原理
Mysql主从模式的原理 参考网上的文章加上自己的一点心得体会 MYSQL 主从同步的作用 (1) 数据分布 (2) 负载平衡 (load balancing) (3) 备份 (4) 高可用性 (high availability) 和容错 ? MYSQL 主从同步的原理 ? 大致描述一下过程：从服务器的IO线程从主服务器
Mysql主从模式的原理参考网上的文章加上自己的一点心得体会
MYSQL主从同步的作用
(1) 数据分布
(2) 负载平衡(load balancing)
(3) 备份
(4) 高可用性(high availability)和容错
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MYSQL主从同步的原理
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大致描述一下过程：从服务器的IO线程从主服务器获取二进制日志，并在本地保存为中继日志，然后通过SQL线程来在从上执行中继日志中的内容，从而使从库和主库保持一致。主从同步的详细过程如下：
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1. 主服务器验证连接。
2. 主服务器为从服务器开启一个线程。
3. 从服务器将主服务器日志的偏移位告诉主服务器。
4. 主服务器检查该值是否小于当前二进制日志偏移位。
5.? 如果小于，则通知从服务器来取数据。
6.? 从服务器持续从主服务器取数据，直至取完，这时，从服务器线程进入睡眠，主服务器线程同时进入睡眠。
7. 当主服务器有更新时，主服务器线程被激活，并将二进制日志推送给从服务器，并通知从服务器线程进入工作状态。
8. 从服务器SQL线程执行二进制日志，随后进入睡眠状态。
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通过上面的介绍我们也就理解了，从节点执行命令show slave status\G，为什么只有当Slave_IO及Slave_SQL进程都正常运行时，即YES状态，从节点才能在数据上达到与主节点同步
? show slave status\G结果显示参数可以参考官方手册 http://dev.mysql.com/doc/refman/5.1/en/show-slave-status.html?
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