A simple and easy-to-understand introduction to Redis caching principles

The following Redis Tutorial column will introduce you to the Redis caching principle. I hope it will be helpful to friends in need!

##1. What is Redis

Redis is a high-performance open source Nosql (non-relational database) written in C language, and the data is stored in memory. Redis is stored in key-value format, which is different from traditional relational databases. It does not necessarily follow some basic requirements of traditional databases, for example, it does not follow SQL standards, transactions, table structures, etc. Non-relational databases are strictly not a database, but a collection of structured data storage methods. Data structures in Java: String, array, list, set map... Redis provides many methods that can be used to access data in various data structures.

2. Features (Advantages)

1. Data is stored in memory, with fast access speed and strong concurrency capability

2. It supports stored value types There are relatively more, including string (string), list (linked list), set (set), zset (sorted set - ordered set) and hash (hash type).
3. The emergence of redis has largely compensated for the shortcomings of key/value storage such as memcached. In some cases, it can play a very good supplementary role to relational databases (such as MySQL).
4. It provides Java, C/C, C#, PHP, JavaScript and other clients, which is very convenient to use.
5.Redis supports clustering (master-slave synchronization, load balancing). Data can be synchronized from the master server to any number of slave servers, and the slave server can be the master server associated with other slave servers.
6. Supports persistence and can save data in files on the hard disk
7. Supports subscription/publish function QQ group
1. Data storage: stored in memory, and also Occasionally persist to disk. The access speed is fast, the concurrency capability is strong, and the data will not be lost after power failure.
2. Supports more Value types.
3. Multiple clients (language java php c# js)
4. Support cluster to expand space 8G 8G 16G
5. Open source (free and maintained by many people)

3. Install the Redis server

The official download site of Redis is http://redis.io/download, you can go there to download the latest installation program

3.1. Under windows Installation and use
1. Download the redis program software
Use redisbin32 or redisbin64
2. Green software, no installation required, use directly

3. Start the redis service (with configuration File startup, and startup without configuration file)

4. Connect to redis for operation
cmd>{%redis%}/redis-cli -h ip address-p port number
ip defaults to local -p defaults to 6379
redis-cli -h 172.16.6.248 -p 6379
cmd>{%redis%}/redis-cli

Basic usage
1. 
   

2. Redis persistence configuration

Redis provides two different levels of persistence Method: RDB and AOF, which can be configured by modifying redis.conf.

When the persistence conditions are met, persistence will be saved. Data that has not yet been saved will be stored in the AOF log format. Save it.
When Redis starts, it first parses the log file (a bunch of commands) and restores the data. Then also load the rdb file (take the union).

4.RDB mode

RDB persistence can generate point-in-time snapshots of the data set within a specified time interval. This mode is enabled by default.

How to turn it off rdb mode:
save ""
save 900 1 //At least one change of storage synchronization is required within a period of 900 seconds
save xxx save 60 10000

5 .AOF log append mode

AOF persistently records all write operation commands executed by the server, and restores the data set by re-executing these commands when the server starts. This mode is turned off by default.
How to turn on aof mode:
appendonly yes //yes to turn on, no to turn off
#appendfsync always //Execute fsync every time there is a new command, and put the buffer data into the aof file
#Here we enable everysec
appendfsync everysec //fsync once per second
#appendfsync no //Never fsync (leave it to the operating system to handle, it may take a long time to execute fsync)
Please provide other parameters Let’s take a look at the detailed explanation of the redis.conf configuration file

6. Redis classic practical scenario-caching

1. 6.1 Why use caching

   Store frequently queried data and rarely modified data in the cache to reduce database access and reduce database pressure. The cache is generally in memory and the access speed is relatively fast.

2. 6.2 Which data is suitable to be placed in the cache

   Frequent query: Caching is to provide efficient access to data queries.
   Rarely modified: the cache and database must be modified simultaneously when modifying
   For example: regional data, product classification, data dictionary menu (regardless of permissions)

3. 6.3 Choose the appropriate one Cache

   Hibernate second-level cache, mybatis second-level cache, redis central cache
   Hibernate second-level cache, mybatis second-level cache does not support cluster cache by default, use redis

4. 6.4 How to store data

   1) json: Convert the data to be stored into a json type string
   When saving the cache:
   Java Object--------- -->json string
   Get cache:
   json string-------->Java Object-
   Json framework: jdk-json-lib jackson gson fastjson
   2) Binary storage: Serialize the data to be stored into a binary serialization framework to implement

7. Implement menu caching

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