search
HomeDatabaseRedisExample analysis of Redis persistence mechanism

Redis stores data in memory, and the data will be lost when the process exits. Through Redis's persistence mechanism, data in memory can be stored on disk, and data can be loaded from disk files to refill the memory after a restart.

Redis supports two persistence mechanisms: full mirror RDB and incremental persistence AOF.

RDB is a snapshot of Redis, which stores all unexpired key-value pairs in Redis.

Configure RDB in redis.conf:

dbfilename dump.rdb
dir /var/lib/redis



save 900 1 save 300 10 save 60 10000 save "" stop-writes-on-bgsave-error yes rdbcompression yes rdbchecksum yes

Every time the redis process starts, it will first check whether the rdb file exists, and if it exists, load the contents of the file. into memory.

When redis automatically updates the RDB file, it will fork a sub-process to perform snapshot saving. During the saving period, the main process can provide services normally.

We can also save the snapshot through the command:

  • save: Save the snapshot in a blocking manner, and redis cannot handle other requests during the save period

  • bgsave: Fork a child process to complete the saving work. The normal service of redis will not be affected during the saving period. The

lastsave command can get the latest RDB file creation timestamp, which can be used to check whether the save is successful.

RDB is a database snapshot, and each time it is created, the entire database needs to be written to the file. This is a very time-consuming operation, so it is difficult to perform frequently, and a large amount of data may be lost when an exception occurs.

Redis provides the incremental persistence tool AOF (Append Only ile). AOF performs persistence by recording all write instructions in the Redis database. Instructions are stored in the AOF file in the format of the Redis communication protocol.

When the Redis process starts, it will check whether the AOF file exists. If it exists, the instructions in the AOF will be executed sequentially to restore the data.

Redis will add a log to the AOF file every time it executes a write command, but the new record will not be written to disk immediately (fsync) but cached in the write buffer.

We can configure the strategy of writing the data in the buffer to disk to avoid data loss.

Writing data in the buffer to disk is a time-consuming operation. Frequent disk writing will affect performance, but Redis crashes and loses less data, so we need to make trade-offs based on application scenarios.

AOF may record redundant instructions. If we execute the set instruction 100 times for the same key, there will be 100 records in the AOF file but only the last set instruction will be retained to recover the data. AOF rewriting will organize the AOF file, clean up unnecessary command logs (such as deleting overwritten set commands), and reduce the size of the AOF file.

redis adopts a background rewriting strategy, that is, forking a child process to write the sorted AOF into a temporary file. Use BGREWRITEAOF to manually trigger the background rewrite operation.

Actually AOF rewriting will not read the original AOF file. The child process will have a copy of the current data and directly generate a new AOF file based on the copy.

During the rewriting period, the main process writes the new write operations into the original AOF file and AOF rewrite cache. Even if the rewriting fails, the original AOF file still saves complete data. When the child process completes AOF rewriting, it will send a signal to the main process. After receiving the signal, the main process will write the contents of the AOF rewriting cache into a new AOF file, and then overwrite the original file with the new AOF file.

Configure AOF in redis.conf:

appendonly yes  
  

appendfilename appendonly.aof  
  


appendfsync everysec 

    no-appendfsync-on-rewrite no   
  


auto-aof-rewrite-percentage 100  
  

auto-aof-rewrite-min-size 64mb

Redis will record the size of the AOF file at startup or after the last rewrite. If the size of the new data reaches 100% of the original size (auto-aof-rewrite-percentage configuration) triggers rewriting.

The rewrite operation will only be performed when the current AOF file size is greater than auto-aof-rewrite-min-size. Otherwise, rewriting will not be performed even if the amount of new data exceeds the specified percentage. This avoids the problem of frequent initial rewriting caused by the original file being too small.

The above is the detailed content of Example analysis of Redis persistence mechanism. For more information, please follow other related articles on the PHP Chinese website!

Statement
This article is reproduced at:亿速云. If there is any infringement, please contact admin@php.cn delete
es和redis区别es和redis区别Jul 06, 2019 pm 01:45 PM

Redis是现在最热门的key-value数据库,Redis的最大特点是key-value存储所带来的简单和高性能;相较于MongoDB和Redis,晚一年发布的ES可能知名度要低一些,ES的特点是搜索,ES是围绕搜索设计的。

一起来聊聊Redis有什么优势和特点一起来聊聊Redis有什么优势和特点May 16, 2022 pm 06:04 PM

本篇文章给大家带来了关于redis的相关知识,其中主要介绍了关于redis的一些优势和特点,Redis 是一个开源的使用ANSI C语言编写、遵守 BSD 协议、支持网络、可基于内存、分布式存储数据库,下面一起来看一下,希望对大家有帮助。

实例详解Redis Cluster集群收缩主从节点实例详解Redis Cluster集群收缩主从节点Apr 21, 2022 pm 06:23 PM

本篇文章给大家带来了关于redis的相关知识,其中主要介绍了Redis Cluster集群收缩主从节点的相关问题,包括了Cluster集群收缩概念、将6390主节点从集群中收缩、验证数据迁移过程是否导致数据异常等,希望对大家有帮助。

Redis实现排行榜及相同积分按时间排序功能的实现Redis实现排行榜及相同积分按时间排序功能的实现Aug 22, 2022 pm 05:51 PM

本篇文章给大家带来了关于redis的相关知识,其中主要介绍了Redis实现排行榜及相同积分按时间排序,本文通过实例代码给大家介绍的非常详细,对大家的学习或工作具有一定的参考借鉴价值,希望对大家有帮助。

详细解析Redis中命令的原子性详细解析Redis中命令的原子性Jun 01, 2022 am 11:58 AM

本篇文章给大家带来了关于redis的相关知识,其中主要介绍了关于原子操作中命令原子性的相关问题,包括了处理并发的方案、编程模型、多IO线程以及单命令的相关内容,下面一起看一下,希望对大家有帮助。

实例详解Redis实现排行榜及相同积分按时间排序功能的实现实例详解Redis实现排行榜及相同积分按时间排序功能的实现Aug 26, 2022 pm 02:09 PM

本篇文章给大家带来了关于redis的相关知识,其中主要介绍了Redis实现排行榜及相同积分按时间排序,本文通过实例代码给大家介绍的非常详细,下面一起来看一下,希望对大家有帮助。

一文搞懂redis的bitmap一文搞懂redis的bitmapApr 27, 2022 pm 07:48 PM

本篇文章给大家带来了关于redis的相关知识,其中主要介绍了bitmap问题,Redis 为我们提供了位图这一数据结构,位图数据结构其实并不是一个全新的玩意,我们可以简单的认为就是个数组,只是里面的内容只能为0或1而已,希望对大家有帮助。

一起聊聊Redis实现秒杀的问题一起聊聊Redis实现秒杀的问题May 27, 2022 am 11:40 AM

本篇文章给大家带来了关于redis的相关知识,其中主要介绍了关于实现秒杀的相关内容,包括了秒杀逻辑、存在的链接超时、超卖和库存遗留的问题,下面一起来看一下,希望对大家有帮助。

See all articles

Hot AI Tools

Undresser.AI Undress

Undresser.AI Undress

AI-powered app for creating realistic nude photos

AI Clothes Remover

AI Clothes Remover

Online AI tool for removing clothes from photos.

Undress AI Tool

Undress AI Tool

Undress images for free

Clothoff.io

Clothoff.io

AI clothes remover

AI Hentai Generator

AI Hentai Generator

Generate AI Hentai for free.

Hot Article

Repo: How To Revive Teammates
1 months agoBy尊渡假赌尊渡假赌尊渡假赌
R.E.P.O. Energy Crystals Explained and What They Do (Yellow Crystal)
2 weeks agoBy尊渡假赌尊渡假赌尊渡假赌
Hello Kitty Island Adventure: How To Get Giant Seeds
1 months agoBy尊渡假赌尊渡假赌尊渡假赌

Hot Tools

SublimeText3 Linux new version

SublimeText3 Linux new version

SublimeText3 Linux latest version

SublimeText3 Chinese version

SublimeText3 Chinese version

Chinese version, very easy to use

EditPlus Chinese cracked version

EditPlus Chinese cracked version

Small size, syntax highlighting, does not support code prompt function

WebStorm Mac version

WebStorm Mac version

Useful JavaScript development tools

Notepad++7.3.1

Notepad++7.3.1

Easy-to-use and free code editor