【1】 Introduction to redis

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One 、Redis brief introduction

Redis What is it? ？

• Redis It's open source （BSD The license ） Of , Data structure storage system in memory , It can be used as a database 、 Caching and message middleware ;
• Redis Support multiple types of data structures , Such as character string （strings）, hash （hashes）, list （lists）, aggregate （sets）, Ordered set （sorted sets） , Range queries , bitmaps, hyperloglogs and Geographical space （geospatial） Index radius query ;
• Redis Built in copy （replication）,LUA Script （Lua scripting）,LRU Driving events （LRU eviction）, Business （transactions） And different levels of Disk persistence （persistence）;
• Redis adopt sentry （Sentinel） And clusters （Cluster） Provide high availability （high availability）.

Redis characteristic

• Fast

  • Single node read 110000 Time /s, Write 81000 Time /s
  • Data is stored in memory
  • use C Language implementation , Closer to the operating system
  • Single thread Architecture ,6.0 Start to support multithreading （CPU、IO Read and write load ）

• Persistence

  • Data updates will be saved asynchronously to the hard disk （RDB and AOF）

• Multiple data structures - It's not just about supporting simple key-value Type data , And support ： character string 、hash、 list 、 aggregate 、 Ordered set ,

• Support for multiple programming languages

• Rich in functions

  • HyperLogLog、GEO、 Publish subscribe 、Lua Script 、 Business 、Pipeline、Bitmaps,key Be overdue

• Simple and stable

  • Less source code 、 Single thread model

• Master slave copy

• Redis Support data backup （master-slave） With clusters （ Fragmentation storage ）, And have a sentinel monitoring mechanism .

• Redis All operations of are atomic , meanwhile Redis It also supports atomic execution after several operations are combined

Redis Typical usage scenarios

cache

Counter (inc command )

Message queue ( General message queues use special middleware ),

Ranking List ( Ordered set implementation )

Social networks ( give the thumbs-up , And so on , Social network traffic is generally large , Traditional relational database is not suitable )

Distributed session ( So much tomcat share session)

Distributed lock

Redis High concurrency principle

1. Redis Is a pure memory database , It's usually a simple access operation , Threads take up a lot of time , The time spent is mainly focused on IO On , So the reading speed is fast
2. Redis Use non blocking IO,IO Multiplexing , Single thread used to poll descriptor , Open database 、 Turn off 、 read 、 Write all converted to events , Reduce context switching and competition during thread switching .
3. Redis Single thread model is adopted , Ensure the atomicity of each operation , It also reduces context switching and competition of threads .
4. Redis Storage structure diversification , Different data structures optimize data storage , For example, compressed table , Compress and store short data , Again , Jump watch , Use ordered data structure to speed up reading .
5. Redis Using the event separator realized by ourselves , High efficiency , Non blocking internal execution , Large throughput .

Article reference ：https://mp.weixin.qq.com/s/-3fcK4WspGk6SEsaVrdx8A