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HomeDatabaseMysql TutorialRedis学习之主从复制问题和扩容问题

一、解决主从复制问题 当使用Redis作为存储引擎的时候,并且使用Redis读写分离,从机作为读的情况,从机宕机或者和主机断开连接都需要重新连接主机,重新连接主机都会触发全量的主从复制,这时候主机会生成内存快照,主机依然可以对外提供服务,但是作为读的

一、解决主从复制问题

当使用Redis作为存储引擎的时候,并且使用Redis读写分离,从机作为读的情况,从机宕机或者和主机断开连接都需要重新连接主机,重新连接主机都会触发全量的主从复制,这时候主机会生成内存快照,主机依然可以对外提供服务,但是作为读的从机,就无法提供对外服务了,如果数据量大,恢复的时间会相当的长。为了解决Redis主从Copy的问题,有如下两个解决方案:

  1. 主动复制
    所谓主动复制,就是业务层双写多个Redis,避开Redis自带的主从复制。但是自己干同步,就会产生一致性问题,为了保证主从一致,需要加入一系列的验证机制。而且这样的做法,会降低系统性能。
  2. 修改源代码,支持增量同步
    Redis写AOF文件,关闭Redis rewrite AOF文件功能,为了避免文件过大,可以自己实现文件分割功能。
    在业务低峰时期,生成内存快照,并记录快照时刻AOF所在的点。
    当从机重连的时候,从机发送同步命令给主机,主机收到命令后,把最新的快照文件发送给从机,从机从快照文件中恢复,并且获得了该快照对应的AOF点,从机将AOF点发送给主机,主机将AOF文件中该点之后的所有数据操作同步给从机,达到增量同步的效果。

二、解决扩容问题

Redis作者的思路是:Redis Presharding
预算设定Redis instances数量,假设实例数量n,n = 机器数*单台机器redis实例数
后期扩展只需要将旧机器上的部分redis实例迁移到新的机器上,达到平滑扩容。
迁移步骤如下:

  1. 在新的机器上创建实例,并且每个实例设置为被迁移实例的从机。
  2. 主从复制完成之后,设置程序将新的实例作为主。
  3. 停止旧的实例

经过如上步骤之后,旧机器的内存就变大了,最后内存最大为每台机器一个Redis实例。

按作者文章中所说的,一个机器启动多个实例,其实并不会耗费太多资源,因为Redis够轻量,另外多个实例一个接一个的重写AOF文件或者生成内存快照,可以降低内存的占用,而不影响对外的服务。

Redis学习之主从复制问题和扩容问题,首发于Programer. 大猫。

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