Why is redis fast? Message queue, single thread

Why fast ？

1. Memory based :Redis Is to use memory storage , No disk IO Overhead on . Data is in memory , Fast reading and writing .

2. Single threaded implementation （ Redis 6.0 before ): Redis Use a single thread to process requests , It avoids the overhead of thread switching and lock resource contention among multiple threads .

3.IO Multiplexing model :Redis use IO Multiplexing technology .Redis Polling descriptors using a single thread , Convert all database operations into events , Not in the network IO Waste too much time on .

4. Efficient data structure :Redis Each of the underlying data types has been optimized , The purpose is to pursue faster speed .

redis Why single thread

1、 Single thread implementation can avoid excessive context switching overhead . The program always runs within a single thread in the process , There is no scenario of multithreading switching .

2、 Avoid the overhead of synchronization mechanism . If Redis Choose the multithreading model , The problem of data synchronization needs to be considered , Some synchronization mechanisms will be introduced , It will lead to more overhead in the process of operating data , It increases the complexity of the program and reduces the performance at the same time .

3、 Implement a simple , Convenient maintenance . If Redis Use multithreading mode , Then thread safety must be considered in the design of all underlying data structures , that Redis The implementation of will become more complex .

Application scenarios

Redis What are the application scenarios ?

1、 Caching hot data , Relieve the pressure of database .

2、 utilize Redis Atomic self increasing operation , The function of counter can be realized , For example, count the number of user likes 、 Number of user visits, etc .

3、 As a simple message queue , Implement asynchronous operations .

4、 Speed governor , It can be used to limit the frequency of a user accessing an interface , For example, the second kill scenario is used to prevent unnecessary pressure caused by users' fast clicking .

5、 Friend relationship , Use some of the commands of the collection , For example, intersection 、 Combine 、 Difference set, etc , Realize common friends 、 Common hobbies and other functions .

redis How to implement message queuing

1、 Use list , Let the producer use the task LPUSH Put the command into the list , Consumers keep using RPOP Take the task from the list .

2、 Publish subscribe mode . Be similar to MQ Theme mode . Only messages published after subscription can be consumed , A message can be consumed by multiple subscribers .

3、 Delay queue . Use sortedset, Take the time stamp as score, The content of the message is key, call zadd To produce news , Consumers use zrangebyscore` Instructions for N Second before the data polling for processing .