Basic understanding of initial redis

One 、 understand Redis

 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 . It supports multiple types of data structures , Such as character string （strings）, hash （hashes）, list （lists）, aggregate （sets）, Ordered set （sorted sets） And scope query , 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）, And pass Redis sentry （Sentinel） And automatic Partition （Cluster） Provide high availability （high availability）

Two 、 Master the basics

1、redis The default is 16 A database （ Default No 0 individual ）

—— How to view ？

• Get into /usr/local/etc Under the table of contents ： cd /usr/local/etc
• see redis Profile view ：vim redis.conf

notes ： Or directly enter the directory through visit , Open with text editor

Can pass select Command to switch databases

127.0.0.1:6379> select 3   #  Switch to 3 The database 
OK
127.0.0.1:6379[3]> set name wpf  # set set key value 
OK
127.0.0.1:6379[3]> set age 21
OK
127.0.0.1:6379[3]> dbsize   #  see DB( library ) size 
(integer) 2
127.0.0.1:6379[3]> 

2、 Why? redis The default port number for is 6379

6379 It's on the Jiugongge button of the mobile phone ‘ MERZ ’ The corresponding number , and MERZ From the Italian singer Alessia Merz Name .MERZ For a long time Redis author antirez And his friends as a byword for stupidity . later Redis The author is developing Redis This port is selected when

3、redis It's single threaded ！

Redis It's based on memory operations ,Redis The performance bottleneck is not CPU, But according to the memory and network bandwidth of the machine , Since a single thread is easy to implement , and CPU Not a bottleneck , So use a single thread ！

Redis yes C Written language , The official data is 100000+ Of QPS, It's no better than using the same key-value Of Memecache Bad ！

Single thread cannot play multi-core CPU performance , You can open multiple... In a single machine Redis Examples to improve ！

4、redis Why is single thread so fast ？

myth 1： High performance servers must be multithreaded ？

myth 2： Multithreading must be more efficient than single thread ！（ Ignored CPU Context switch of ）

—— Speed from high to low ：CPU > Memory > Hard disk

1. Memory based , Memory is very fast in reading and writing ;
2. Single thread , Save a lot of context switching time ;（ And locking consumption , And deadlock problems ）
3. redis Using multiplexing technology , Can handle concurrent connections . Non blocking IO Internal implementation adoption epoll, Adopted epoll+ Simple event framework implemented by ourselves .epoll Reading in Chinese 、 Write 、 close 、 Connections are converted to events , And then use it epoll Multiplexing characteristics of , Never in io Waste a little time .

The core ：Redis Is to put all the data in memory , Using a single thread to operate is the most efficient ！（ Multithreading exists CPU Context switch back ： Time consuming operations ！）, For memory systems , If there is no context switching, the efficiency is the highest ！ Read and write many times in the same CPU On —— Best solution ！

5、IO Multiplexing technology

redis Using the network IO Multiplexing technology to ensure multiple connections , High throughput of the system .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 .

1. multiple ： multiple socket ( The Internet ) Connect
2. Reuse ： To reuse a thread .

summary ： Multiplexing allows a single thread to efficiently process multiple connection requests （ Minimize the network IO Time consumption of ）, And Redis It's very fast to manipulate data in memory （ Operations in memory will not be a performance bottleneck here ）, The above two main factors contribute to Redis With high throughput .

 

Common orders

1、 Switch database
select [ index ]

2、 View all key
keys *

3、 Get a single key Value
get [key name ]

4、 Clear all key values of the current library
flushdb

5、 Clear all library key values
flushall

6、 Judge key Whether there is （ Equate to sql Of =, Instead of like; for example where name=' Zhang San '）
exists [ key name ]

7、 Remove a from the current library key（1 Represents the current library , Used in test select Switch to Library 3, Remove or 1 Instead of 3）
move [ key name ] 1    —— grammar ：move [ key name ] db

8、 Set up key The expiration time of , The unit is in seconds （ example ：expire name 10）
expire [ key name ] [ Number of seconds ] 

9、 View the current key The remaining expiration time of
ttl  [ key name ] 

10、 View the current key The type of （string、int、map....）
type [ key name ]