Redis review summary

Redis

Redis What can you do with it

1.Redis The longest is used for caching , It is the first middleware to realize distributed cache
2.Redis Can be used as a database , Realize such as like , Focus on , Ranking and other Internet demand with high performance requirements
3.Redis It can be used as a calculation tool , At a very small cost , Statistics such as PV/UV, User online days and other data
4.Redis There are many other scenarios , for example ： Distributed locks can be implemented , It can be used as a message queue .

Redis How is it different from traditional relational database ？

Redis It's based on key value pairs NoSQL database , The value of key value pair is composed of a variety of data structures and algorithms .Redis All the data is stored in memory , So its speed is amazing , The reading and writing performance can reach 10 ten thousand / second , Far beyond relational databases

Relational database is based on two-dimensional data table to store data , Its data format is more rigorous , And support relationship query . The data of relational database is stored on disk , It can store a large amount of data , But the performance is far inferior to Redis

difference ：
NoSQL Store in memory , Relational databases are stored on disk

Redis What are the data types

1.Redis Support 5 Core data types in , They are strings , Hash , list , aggregate , Ordered set
2.Redis It also provides Bitmap,HyperLogLog,Geo type , But these are based on the above core data types
3.Redis stay 5.0 The new increased Streams data type , It's a powerful 、 Support multicast 、 Persistent message queue .

Redis Why is it single threaded but so fast

1. Single thread avoids the consumption caused by thread switching and contention
2.Redis Most operations are done in memory
3.Redis Adopted IO Multiplexing mechanism , Make it on the Internet IO A large number of client requests can be processed simultaneously in the operation , Achieve high throughput .

set and zset What's the difference

set： I.e. set

The elements in the collection are unordered 、 Non repeatable , A collection can store up to 232-1 Elements ;

In addition to supporting the addition, deletion, modification and query of elements , It also supports the intersection of multiple sets 、 Combine 、 Difference set .

zset： It's an ordered set

Ordered sets retain the feature that set elements cannot be repeated ;

An ordered set sets a score for each element , And take this as the basis for sorting ;

Ordered collections cannot contain the same elements , But the scores of different elements can be the same .

1.7 The way Redis Medium watch command

Refer to the answer

A lot of times , Ensure that the data in the transaction has not been modified by other clients before executing the transaction .Redis Provides watch Command to solve such problems , This is an optimistic lock mechanism . Client pass watch command , Require the server to one or more key To monitor , If before the client executes the transaction , these key There is a change , The server will refuse to execute the transaction submitted by the client , And return a null value to it .

1.8 say something Redis in List Structure related operations

Refer to the answer

Lists are linearly ordered data structures , Its internal elements can be repeated , And a list can store up to 2^32-1 Elements . The list contains the following common commands ：

lpush/rpush： From the left side of the list / Add data on the right ;

lrange： Specify the index range , And return the data in this range ;

lindex： Returns the data at the specified index ;

lpop/rpop： From the left side of the list / A data pop-up on the right ;

blpop/brpop： From the left side of the list / A data pop-up on the right , If the list is empty, it will enter the blocking state .

1.9 How do you design Redis The expiration time of ？

Refer to the answer

No expiration time is set for hotspot data , To achieve “ Physics ” The on the never expires , It can avoid the problem of cache breakdown ;

When setting the expiration time , You can attach a random number , Avoid a lot of key At the same time , Cause cache avalanche .