MySQL主从、主主复制及高可用性
将master服务器中主数据库的ddl和dml操作通过二进制日志传到slaves服务器上,然后在master服务器上将这些日志文件重新执行,从而
一:MySQL复制:
MySQL复制简介:
将master服务器中主数据库的ddl和dml操作通过二进制日志传到slaves服务器上,然后在master服务器上将这些日志文件重新执行,从而使得slave服务器和master服务器上的数据信息保持同步。
Mysql复制的原理:
将数据分布到多个系统上去,是通过将Mysql的某一台master主机的数据复制到其它(slave)主机上,并重新执行一遍来实现的;
复制过程中一个服务器充当master服务器,而一台或多台其它服务器充当slave服务器。master服务器将更新写入二进制日志文件,并维护文件的一个索引以跟踪日志循环。
这些日志可以记录发送到slave服务器的更新。当一个slaves服务器连接master服务器时,它通知master服务器从服务器在日志中读取的最后一次成功更新的位置。slave服务器接收从那时起发生的任何更新,,然后封锁并等待master服务器通知新的更新。
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mysql复制的优点:
在slave服务器上执行查询操作,降低master服务器的访问压力
当master服务器上出现了问题可以切换到slave服务器上,不会造成访问中断等问题
在slave服务器上进行备份,以避免备份期间影响master服务器的服务使用及日常访问
Mysql自身的复制功能:是构建大型、高性能应用程序的基础。
mysql支持的复制类型:
基于语句的复制:在主服务器上执行的SQL语句,在从服务器上执行同样的语句。MySQL默认采用基于语句的复制,效率比较高。一旦发现没法精确复制时,会自动选着基于行的复制。
基于行的复制:把改变的内容复制过去,而不是把命令在从服务器上执行一遍. 从mysql5.0开始支持
混合类型的复制::默认采用基于语句的复制,一旦发现基于语句的无法精确的复制时,就会采用基于行的复制。
MySQL复制技术的特点:
数据分布 (Data distribution )
备份(Backups)
负载平衡(load balancing)
高可用性和容错性 High availability and failover
复制的工作过程:
master将改变记录到二进制日志(binary log)中(这些记录叫做二进制日志事件,binary log events);
slave将master的binary log events拷贝到它的中继日志(relay log);
slave重做中继日志中的事件,将改变反映它自己的数据。
第一步:master记录二进制日志。在每个事务更新数据完成之前,master在二日志记录这些改变。MySQL将事务串行的写入二进制日志,即使事务中的语句都是交叉执行的。在事件写入二进制日志完成后,master通知存储引擎提交事务;
第二步:slave将master的binary log拷贝到自己的中继日志。首先,slave开始一个工作线程——I/O线程。I/O线程在master上打开一个普通的连接,然后开始binlog dump process。Binlog dump process从master的二进制日志中读取事件,如果已经跟上master,它会睡眠并等待master产生新的事件。I/O线程将这些事件写入中继日志;
第三步:SQL slave thread(SQL从线程)处理该过程的最后一步。SQL线程从中继日志读取事件,并重放其中的事件而更新slave的数据,使其与master中的数据一致。只要该线程与I/O线程保持一致,中继日志通常会位于OS的缓存中,所以中继日志的开销很小。
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