Redis数据持久化机制AOF原理分析之配置详解
本文所引用的源码全部来自Redis2.8.2版本。 Redis的配置文件为redis.conf, 对配置文件的解析代码见config.c 原创文章转载请注明,本文来自http://blog.csdn.net/acceptedxukai/article/details/18135219 AOF实现机制简介 AOF 即Append Only File,实现机制:R
本文所引用的源码全部来自Redis2.8.2版本。
Redis的配置文件为redis.conf, 对配置文件的解析代码见config.c
原创文章转载请注明,本文来自http://blog.csdn.net/acceptedxukai/article/details/18135219
AOF实现机制简介
AOF 即Append Only File,实现机制:Redis将数据库做个快照,遍历所有数据库,将数据库中的数据还原为跟客户端发送来的指令的协议格式的字符串,然后Redis新建一个临时文件将这些快照数据保存,待快照程序结束后将临时文件名修改为正常的aof文件名,原有的文件则自动丢弃,由于在快照进行的过程中可能存在新增的命令修改了数据库中的数据,则在快照程序结束后需要将新修改的数据追加到aof文件中,后续的从客户端过来的命令都会不断根据不同的安全级别写到磁盘里面去。这样就支持了实时的持久化,只是可能会有短时间内的数据丢失,对一般系统还是可以容忍的。
配置文件redis.conf中有关AOF参数配置解释
appendonly
含义:Redis Server是否开启AOF持久化机制
在config.c函数loadServerConfigFromString解析代码为
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appendfsync
含义:Redis将OS数据缓冲区中数据刷新到磁盘的策略
# appendfsync always 只要有新添加的数据就fsync
appendfsync everysec 支持延迟fsync
# appendfsync no 不需要fsync
config.c中解析代码
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no-appendfsync-on-rewrite
含义:当rewrite AOF子进程或RDB子进程正在执行时,Server是否支持fsync,即当新修改的数据写入AOF文件后,是否将数据刷新到硬盘
config.c中解析代码
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server.aof_no_fsync_on_rewrite控制该机制的实现代码在aof.c的flushAppendOnlyFile函数中,具体代码为
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appendfilename
含义:AOF的文件名
auto-aof-rewrite-percentage 100
auto-aof-rewrite-min-size 64mb
这两个配置就暂不解释,见下面redisServer结构体中中有关AOF参数的注释
redisServer数据结构中有关AOF的参数
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字符串aof_buf与链表aof_rewrite_buf_blocks分别是追加AOF文件与rewrite AOF文件后处理差异数据的重要参数
initServerConfig函数对AOF参数的初始化及注释
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其中aof_current_size参数未初始化,该值的初始化在Server启动加载AOF文件数据时初始化。
小结
本文就是简单介绍Redis中有关AOF机制实现的相关参数的意义,方便对接下来AOF数据持久化机制的理解,AOF机制的实现比较复杂,大致分为Server启动加载AOF文件数据、将新的数据追加到AOF文件中、自动rewrite AOF文件、客户端请求BGREWRITEAOF指令四个部分,下面的博客将介绍这三个部分的实现。

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