MySQL分布式概念(读写分离)
作用
对数据进行备份，实现高可用HA通过读写分离，提高吞吐量，实现高性能
原理
MySQL的复制是一个异步的赋值过程过程本质为Slave从Master端获取Binary Log，然后再在自己身上完全顺序的执行日志中所记录的各种操作MySQL复制的基本过程如下：
Slave 上面的IO线程连接上Master，并请求从指定日志文件的指定位置之后的日志内容。Master接受到来自Slave的IO线程的请求后，通过负责复制的IO线程根据请求信息读取日志信息，返回给Slave端的IO线程。Slave的IO线程接收到信息后，将接收到的日志内容依次写入到Slave端的Relay Log文件。Slave的SQL线程检测到Relay Log中新增加了内容后，会马上解析该文件中的内容，并在自身执行这些原始SQL语句。
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Master
Slave
Datechanges
Read
Write
Replay
Read
Relay
log
I/O
thread
SQL
thread
Binary
log
主库
常用架构
主从架构
性能
一主多从，读写分离，提高吞吐量 可用性
主库单点，一旦挂了，无法写入从库高可用
主备架构
性能
单库读写，性能一般 高可用
高可用，一旦主库挂了，就启用备库
（这种方案被阿里云，美团等企业广泛使用）
高可用复合框架（结合两种框架的优点设计）
性能
读写分离，提高吞吐量 可用性
高可用，一旦主库挂了，就启用备库
