search
HomeDatabaseRedisHow does redis persist data?

How does redis persist data?

Nov 21, 2019 am 10:03 AM
redis

Redis is called an in-memory database because it stores all its data in memory, so Redis has strong speed performance. However, precisely because the data is stored in memory, when Redis is restarted, all Data stored in memory will be lost. In order to make data persistent, Redis provides two methods: RDB method and AOF method.

How does redis persist data?

1. RDB method

RDB method persistence is completed through snapshotting. Under certain conditions, Redis will automatically generate a copy of all the data in the memory and store it on the hard disk. This process is called a "snapshot". "Snapshot" is similar to taking a photo. The moment you press the shutter, the photo you freeze is called a "snapshot".

# Redis There are 4 cases of snapshots on the data: (Recommended Learning: Redis Video Tutorial )

## automatically;


When the user executes the SAVE or BGSAVE command;

executes the FLUSHALL command;

when executing replication.

2. AOF method

Persistence is achieved through RDB. Once Redis exits abnormally, all data changed after the last snapshot will be lost. In order to reduce the risk of data loss caused by process termination, the AOF method can be used to achieve data persistence.


AOF persistence records every write and delete operation processed by the server in the form of a log. Query operations will not be recorded, but will be recorded in the form of text. Details can be seen in the file. operation records.

Her appearance is to make up for the shortcomings of RDB (data inconsistency), so it uses the form of a log to record each write operation and append it to the file. When Redis is restarted, the write instructions will be executed from front to back based on the contents of the log file to complete the data recovery work.

By default, Redis does not enable AOF persistence. It can be started through the appendonly parameter: appendonly yes


After AOF persistence is enabled, each execution will change Redis. Data command, Redis will write the command to an AOF format file on the hard disk, that is, the .aof format file stores some redis instructions.

It should be noted at this time that when data in Redis is frequently manipulated, the memory occupied by the AOF format file will become larger and larger, and there will be many useless instructions, such as continuously executing set foo 1, set foo 2, set foo 3.

Then the first two instructions are meaningless. Redis is very powerful. It will automatically delete meaningless instructions. That is, whenever a certain condition is reached, Redis will automatically rewrite the AOF file, and this condition Can be set in the configuration file. The rewriting process is only related to memory data and has nothing to do with the previous AOF file. This is similar to RDB.


When synchronizing hard disk data, due to the cache mechanism of the operating system, the data is not actually written to the hard disk, but enters the system's hard disk cache. By default, the system will perform a synchronization operation every 30 seconds. During these 30 seconds, if the system exits abnormally, the data in the hard disk memory will be lost.

Redis allows RDB and AOF modes to be turned on at the same time, which not only ensures data security, but also makes backup operations very easy. AOF can effectively reduce the possibility of data loss, and RDB can make data backup easy to achieve.

The above is the detailed content of How does redis persist data?. For more information, please follow other related articles on the PHP Chinese website!

Statement
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn
Redis: Exploring Its Core Functionality and BenefitsRedis: Exploring Its Core Functionality and BenefitsApr 30, 2025 am 12:22 AM

Redis's core functions include memory storage and persistence mechanisms. 1) Memory storage provides extremely fast read and write speeds, suitable for high-performance applications. 2) Persistence ensures that data is not lost through RDB and AOF, and the choice is based on application needs.

Redis's Server-Side Operations: What It OffersRedis's Server-Side Operations: What It OffersApr 29, 2025 am 12:21 AM

Redis'sServer-SideOperationsofferFunctionsandTriggersforexecutingcomplexoperationsontheserver.1)FunctionsallowcustomoperationsinLua,JavaScript,orRedis'sscriptinglanguage,enhancingscalabilityandmaintenance.2)Triggersenableautomaticfunctionexecutionone

Redis: Database or Server? Demystifying the RoleRedis: Database or Server? Demystifying the RoleApr 28, 2025 am 12:06 AM

Redisisbothadatabaseandaserver.1)Asadatabase,itusesin-memorystorageforfastaccess,idealforreal-timeapplicationsandcaching.2)Asaserver,itsupportspub/submessagingandLuascriptingforreal-timecommunicationandserver-sideoperations.

Redis: The Advantages of a NoSQL ApproachRedis: The Advantages of a NoSQL ApproachApr 27, 2025 am 12:09 AM

Redis is a NoSQL database that provides high performance and flexibility. 1) Store data through key-value pairs, suitable for processing large-scale data and high concurrency. 2) Memory storage and single-threaded models ensure fast read and write and atomicity. 3) Use RDB and AOF mechanisms to persist data, supporting high availability and scale-out.

Redis: Understanding Its Architecture and PurposeRedis: Understanding Its Architecture and PurposeApr 26, 2025 am 12:11 AM

Redis is a memory data structure storage system, mainly used as a database, cache and message broker. Its core features include single-threaded model, I/O multiplexing, persistence mechanism, replication and clustering functions. Redis is commonly used in practical applications for caching, session storage, and message queues. It can significantly improve its performance by selecting the right data structure, using pipelines and transactions, and monitoring and tuning.

Redis vs. SQL Databases: Key DifferencesRedis vs. SQL Databases: Key DifferencesApr 25, 2025 am 12:02 AM

The main difference between Redis and SQL databases is that Redis is an in-memory database, suitable for high performance and flexibility requirements; SQL database is a relational database, suitable for complex queries and data consistency requirements. Specifically, 1) Redis provides high-speed data access and caching services, supports multiple data types, suitable for caching and real-time data processing; 2) SQL database manages data through a table structure, supports complex queries and transaction processing, and is suitable for scenarios such as e-commerce and financial systems that require data consistency.

Redis: How It Acts as a Data Store and ServiceRedis: How It Acts as a Data Store and ServiceApr 24, 2025 am 12:08 AM

Redisactsasbothadatastoreandaservice.1)Asadatastore,itusesin-memorystorageforfastoperations,supportingvariousdatastructureslikekey-valuepairsandsortedsets.2)Asaservice,itprovidesfunctionalitieslikepub/submessagingandLuascriptingforcomplexoperationsan

Redis vs. Other Databases: A Comparative AnalysisRedis vs. Other Databases: A Comparative AnalysisApr 23, 2025 am 12:16 AM

Compared with other databases, Redis has the following unique advantages: 1) extremely fast speed, and read and write operations are usually at the microsecond level; 2) supports rich data structures and operations; 3) flexible usage scenarios such as caches, counters and publish subscriptions. When choosing Redis or other databases, it depends on the specific needs and scenarios. Redis performs well in high-performance and low-latency applications.

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

Video Face Swap

Video Face Swap

Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Tools

Dreamweaver Mac version

Dreamweaver Mac version

Visual web development tools

SublimeText3 English version

SublimeText3 English version

Recommended: Win version, supports code prompts!

MinGW - Minimalist GNU for Windows

MinGW - Minimalist GNU for Windows

This project is in the process of being migrated to osdn.net/projects/mingw, you can continue to follow us there. MinGW: A native Windows port of the GNU Compiler Collection (GCC), freely distributable import libraries and header files for building native Windows applications; includes extensions to the MSVC runtime to support C99 functionality. All MinGW software can run on 64-bit Windows platforms.

Atom editor mac version download

Atom editor mac version download

The most popular open source editor

Safe Exam Browser

Safe Exam Browser

Safe Exam Browser is a secure browser environment for taking online exams securely. This software turns any computer into a secure workstation. It controls access to any utility and prevents students from using unauthorized resources.