Notes Introduction, installation and deployment of Redis

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##Article Directory

1. What is Redis
• 2. What can Redis do
• 3. Redis download, installation and deployment
• 4. Some little knowledge of Redis

1. What is Redis

Redis: REmote DIctionary Server (remote dictionary server)

high-performance (key/value) distributed memory database that complies with the BSD protocol. It is also a NoSQL database that runs based on memory and supports persistence, is one of the most popular NoSql databases, also known as data structure server. At the same time, Redis is also a simple, efficient, distributed, memory-based caching tool. After the server is constructed, Key-Value caching services are provided through network connections (similar to databases).

Redis has the following advantages:

• 1. Extremely high performance The reading speed of Redis is 110,000 times/s. The writing speed is 80,000 times/second.
• 2. Rich data types The types supported by Redis include String, Hash, List, Set and Ordered Set database types.
• 3. Atomicity All Redis operations are atomic and wrapped through MULTI and EXEC instructions.
• 4. Rich reading and writing Redis supports publish/subscribe, notification, key expiration and other features.
• 5. High-speed reading and writing Redis uses its own separator. The amount of code is very short and no lock (MySQL) is used, so the efficiency is very high.

Redis also has the following disadvantages:

• 1. Persistence Redis stores data directly in memory. If you want to save the data to the disk, the first method is to use ① scheduled snapshot (snapshot): write the entire database to the disk every once in a while, and write all the data each time, but the cost Very high; the second method is②Append based on statement (aof): Only the changed data is tracked, but the appended log may be too large, and all operations must be re-executed, resulting in slow recovery.
• 2. Memory consumption, the memory occupied is too high.

2. What can Redis do

Examples of common scenarios for Redis are as follows:

• Caching Nowadays, caching is a requirement of almost all medium and large websites. The most effective way to use cache properly is to not only improve the access speed of the website, but also greatly reduce the pressure on the database. Redis provides key expiration function and flexible key elimination strategy.
  

• Ranking list Such as Taobao's monthly sales list, product new listings by time, etc. The ordered set data structure provided by Redis can implement various complex ranking applications.
  

• Counter Such as the number of views of products on e-commerce websites, the number of video plays on video websites, etc. In order to ensure the real-time performance of the data, 1 must be given for each browsing. When the concurrency is high, it will undoubtedly be a challenge and pressure to request database operations every time. The incr command provided by Redis implements counter functions and memory operations with very good performance and is very suitable for these counting scenarios.
  

• Distributed session In cluster mode, when there are not many applications, it is generally sufficient to use the session replication function that comes with the container. In the application In increasingly complex systems, session services centered on in-memory databases such as Redis are generally built. Sessions are no longer managed by containers, but by session services and in-memory databases.
  

• Distributed lock The technical challenge brought by distributed technology is concurrent access to the same resource, such as global ID, inventory reduction, flash sale, etc. Scenarios with low concurrency can be implemented using database pessimistic locks and optimistic locks. However, in scenarios with high concurrency, it is not ideal to use database locks to control concurrent access to resources, which greatly affects the performance of the database. . You can use the setnx function of Redis to write distributed locks. If the setting returns 1, it means the lock acquisition is successful. Otherwise, the lock acquisition fails. There are more details to consider in actual applications.
  

• Social Network Likes, dislikes, following/being followed, mutual friends, etc. are the basic functions of social networking sites. The number of visits to social networking sites usually comes from It is relatively large, and traditional relational database types are not suitable for storing this type of data. The hash, set and other data structures provided by Redis can easily implement these functions.
  

• Latest list Redis list structure, LPUSH can insert a content ID as a keyword at the head of the list, LTRIM can be used to limit the number of lists, so The list is always N IDs. There is no need to query the latest list, just go to the corresponding content page based on the ID.
  

• Message system
  Message queue is a necessary middleware for large websites, such as ActiveMQ, RabbitMQ, Kafka and other popular message queue middleware. It is mainly used for business decoupling, Traffic peak shaving and asynchronous processing of services with low real-time performance. Redis provides publish/subscribe and blocking queue functions, which can implement a simple message queue system. However, this cannot be compared with professional message middleware.

3. Redis download, installation and deployment

Redis English official website.
Redis Chinese website.

Since 99% of enterprises doing Redis development are using and installing the Linux version, this article only introduces the installation and operation under Linux. Friends can use Baidu for installation under Windows. Go to the official website above and click Download to download the .gz installation package and place it in the /opt directory under Linux (I installed version 6.0.5 of Redis here).

• The decompression command is: tar -zxvf redis-6.0.5.tar.gz

The above command only decompresses Redis. If you want to install Redis, you need a gcc environment in your Linux system. If not, you can use yum install gcc-c to install it, and then use gcc -v to check the version.

If the Linux environment already has a gcc environment, directly use the following command to install:

• The installation command is: make install

After installation, the default is that it cannot start automatically like Tomcat. You can modify the daemonize attribute in the redis.conf file to yes.

• Start the redis service: redis-server /myredis/redis.conf(This is the redis configuration file after modifying the properties)

View Whether the background Redis service is started:

• ps -ef|grep redis

Start the Redis service:

• redis-cli -p 6379
  

Close normally and the data will be saved
Use in the redis command lineshutdownCommand shutdown.

Abnormal shutdown may easily lead to data loss
Power outage, manually kill the redis process, etc.

Several other redis commands

4. Some little knowledge of Redis

Redis is a single process and uses a single process model to handle client requests. Responses to events such as reading and writing are accomplished by wrapping the epoll function. The actual processing speed of Redis depends entirely on the execution efficiency of the main process.

epoll is an improved version of epoll made by the Linux kernel to handle large batches of file descriptors. It is an enhanced version of the multiplexed IO interface select/poll under Linux. It can significantly improve the performance of programs in a large number of System CPU utilization when there are only a few active concurrent connections.

• Redis has 16 databases by default. The subscripts start from zero. The initial default is to use the zero database. You can use the SELECT <dbid></dbid> command to connect. specified database.
  

• dbsize command can view the number of keys in the current database, keys *View all keys.
  

• flushdb: Clear the current library (use with caution)

• ##Flushall: Clear all libraries (use with caution)

• Unified password management, 16 libraries have the same password, either all are OK or none can be connected.

• Redis indexes all start from zero

• The default port of Redis is 6379

More related free learning recommendations: redis introductory tutorial

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