1. The origin of 16 databases
Redis is a dictionary-structured storage server. A Redis instance provides multiple dictionaries for storing data. The client can specify which dictionary to store the data in. This is similar to how multiple databases can be created in a relational database instance (as shown in the figure below), so each dictionary can be understood as an independent database.

Take MySQL instance as an example
Redis supports 16 databases by default, which can be modified by adjusting the databases in the Redis configuration file redis/redis.conf After setting this value, restart Redis to complete the configuration.

After the client establishes a connection with Redis, database No. 0 will be selected by default, but you can use the SELECT command to change the database at any time.
In actual projects, you can specify the database in the form of a Redis configuration file, as shown in the figure below

2. Correctly understand Redis "Database" concept
Since Redis does not support custom database names, each database is named with a number. Developers need to record the correspondence between the stored data and the database. In addition, Redis does not support setting different access passwords for each database, so a client can either access all databases, or all databases have no permission to access. However, to correctly understand the "database" concept of Redis, we have to mention a command:

This command can clear all database data under the instance, which is different from what we are talking about. It is different from the well-known relational database. Multiple libraries of relational databases are often used to store data for different applications, and there is no way to clear all library data under an instance at the same time. So for Redis, these dbs are more like a namespace and are not suitable for storing data from different applications. For example, you can use database No. 0 to store data in the production environment of an application, and use database No. 1 to store data in the test environment. However, it is not appropriate to use database No. 0 to store the data of application A and use database No. 1 to store the data of application B. It is different. Applications should use different Redis instances to store data. Redis is very lightweight. An empty Redis instance only takes up about 1M, so you don’t have to worry about multiple Redis instances taking up a lot of extra memory.
3. Does one instance support multiple DBs in a cluster?
It should be noted that the above are all based on single Redis. In the case of a cluster, the use of the select command to switch db is not supported because there is only one db0 in Redis cluster mode. To expand on the differences between clusters and stand-alone Reids, interested friends can check out relevant information for a deeper understanding, but we will not discuss them here.
Key batch operation support is limited: For example, mget and mset must be in a slot
Key transaction and Lua support are limited: The key of the operation must be in A node
key is the minimum granularity of data partition: Bigkey partition is not supported
Does not support multiple databases: There is only one db0 in cluster mode
Copy only supports one level: tree copy structure is not supported
The above is the detailed content of What is the database concept of Redis. For more information, please follow other related articles on the PHP Chinese website!
Redis: Improving Application Performance and ScalabilityApr 17, 2025 am 12:16 AMRedis improves application performance and scalability by caching data, implementing distributed locking and data persistence. 1) Cache data: Use Redis to cache frequently accessed data to improve data access speed. 2) Distributed lock: Use Redis to implement distributed locks to ensure the security of operation in a distributed environment. 3) Data persistence: Ensure data security through RDB and AOF mechanisms to prevent data loss.
Redis: Exploring Its Data Model and StructureApr 16, 2025 am 12:09 AMRedis's data model and structure include five main types: 1. String: used to store text or binary data, and supports atomic operations. 2. List: Ordered elements collection, suitable for queues and stacks. 3. Set: Unordered unique elements set, supporting set operation. 4. Ordered Set (SortedSet): A unique set of elements with scores, suitable for rankings. 5. Hash table (Hash): a collection of key-value pairs, suitable for storing objects.
Redis: Classifying Its Database ApproachApr 15, 2025 am 12:06 AMRedis's database methods include in-memory databases and key-value storage. 1) Redis stores data in memory, and reads and writes fast. 2) It uses key-value pairs to store data, supports complex data structures such as lists, collections, hash tables and ordered collections, suitable for caches and NoSQL databases.
Why Use Redis? Benefits and AdvantagesApr 14, 2025 am 12:07 AMRedis is a powerful database solution because it provides fast performance, rich data structures, high availability and scalability, persistence capabilities, and a wide range of ecosystem support. 1) Extremely fast performance: Redis's data is stored in memory and has extremely fast read and write speeds, suitable for high concurrency and low latency applications. 2) Rich data structure: supports multiple data types, such as lists, collections, etc., which are suitable for a variety of scenarios. 3) High availability and scalability: supports master-slave replication and cluster mode to achieve high availability and horizontal scalability. 4) Persistence and data security: Data persistence is achieved through RDB and AOF to ensure data integrity and reliability. 5) Wide ecosystem and community support: with a huge ecosystem and active community,
Understanding NoSQL: Key Features of RedisApr 13, 2025 am 12:17 AMKey features of Redis include speed, flexibility and rich data structure support. 1) Speed: Redis is an in-memory database, and read and write operations are almost instantaneous, suitable for cache and session management. 2) Flexibility: Supports multiple data structures, such as strings, lists, collections, etc., which are suitable for complex data processing. 3) Data structure support: provides strings, lists, collections, hash tables, etc., which are suitable for different business needs.
Redis: Identifying Its Primary FunctionApr 12, 2025 am 12:01 AMThe core function of Redis is a high-performance in-memory data storage and processing system. 1) High-speed data access: Redis stores data in memory and provides microsecond-level read and write speed. 2) Rich data structure: supports strings, lists, collections, etc., and adapts to a variety of application scenarios. 3) Persistence: Persist data to disk through RDB and AOF. 4) Publish subscription: Can be used in message queues or real-time communication systems.
Redis: A Guide to Popular Data StructuresApr 11, 2025 am 12:04 AMRedis supports a variety of data structures, including: 1. String, suitable for storing single-value data; 2. List, suitable for queues and stacks; 3. Set, used for storing non-duplicate data; 4. Ordered Set, suitable for ranking lists and priority queues; 5. Hash table, suitable for storing object or structured data.
How to implement redis counterApr 10, 2025 pm 10:21 PMRedis counter is a mechanism that uses Redis key-value pair storage to implement counting operations, including the following steps: creating counter keys, increasing counts, decreasing counts, resetting counts, and obtaining counts. The advantages of Redis counters include fast speed, high concurrency, durability and simplicity and ease of use. It can be used in scenarios such as user access counting, real-time metric tracking, game scores and rankings, and order processing counting.


Hot AI Tools

Undresser.AI Undress
AI-powered app for creating realistic nude photos

AI Clothes Remover
Online AI tool for removing clothes from photos.

Undress AI Tool
Undress images for free

Clothoff.io
AI clothes remover

AI Hentai Generator
Generate AI Hentai for free.

Hot Article

Hot Tools

SublimeText3 English version
Recommended: Win version, supports code prompts!

mPDF
mPDF is a PHP library that can generate PDF files from UTF-8 encoded HTML. The original author, Ian Back, wrote mPDF to output PDF files "on the fly" from his website and handle different languages. It is slower than original scripts like HTML2FPDF and produces larger files when using Unicode fonts, but supports CSS styles etc. and has a lot of enhancements. Supports almost all languages, including RTL (Arabic and Hebrew) and CJK (Chinese, Japanese and Korean). Supports nested block-level elements (such as P, DIV),

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.

SublimeText3 Chinese version
Chinese version, very easy to use

SublimeText3 Mac version
God-level code editing software (SublimeText3)






