String type and bitmap of redis

redis Operation principle

redis There are many clients connected , Standing on the redis From the perspective of the machine , It's just that there are a lot of socket The connection of , And it's in the kernel
above ,redis It's a process , Processes can call on the kernel epoll, To traverse to find which client sent data （ Here is a single process and single thread to process user data ）.

redis Use

redis The default is 16 Databases


Input ：
Enter basic group

keys * Query all key
FLUSHDB Clear away all key

For the above nx Your order is my current key If it is not set, set ooxx Set successfully , If the key There has been a value 了 ,
Then return to nil （ It is mainly used for acquiring distributed locks , Only one can succeed ）

about xx command , Only when it exists can it be operated .

mset command （ Set up multiple key and value）

append Command and getrange command

redis Forward and reverse indexing

The front is from 0,1,2 At the beginning , The latter is from -1 Beginning to decline , So you can also write in the following way

SETRANGE Set the string in the given range

Get string length

obtain key The corresponding value type （ Mainly to see set Command grouping is in string above ）

Let's take a look at object command

It can see value Code type of （ oriented redis string type , Besides string operation, there are also calculation operations 【 The operation of calculation is numerical 】）

incr and decr Relevant command 【 Can be used to rush to buy , seckill , give the thumbs-up , comments , Details page （ For example, Taobao details page , The backend will definitely initiate an asynchronous query on the number of purchases , check redis, Can avoid and issue , Transaction operation on Database ,
Completely by redis Memory operation replaces ）】

redis Binary security

redis When a process interacts with the outside world , Stream oriented we have byte streams , And character stream , that redis client
At the time of the visit , from socket What you get inside is the data of byte stream , As long as the client and server of both sides have the same
Codec mode , The data will not be destroyed .
Such as set k1 = 9999, perform strlen Output 4,redis The data stored in it is stored according to one character and one byte , direct
Write to the character stream , perform incr Then take out the byte stream and convert it into numerical value , It will be updated after being converted to numerical value key Of encoding
code , As long as it is added successfully, it will be updated to int 了 , If you add it next time, you can directly check this encoding Type , If you add
No int An error is reported for the type
The other is set k2 in , It is Zhan 3 Bytes of （ Software and redis Communications utf-8）
Let's set up another k3 Occupy 2 Bytes （gbk code ）

Then exit with redis-cli --raw To log in , Will trigger a format （ If you don't bring –raw Yes, I can only recognize ascii The code
, In case of excess, it shall be subject to 16 To show , If you add raw Will trigger the format of the code set ）

key There are encoding Words , It is equivalent to an optimization , To judge whether my current operation is feasible

getset command

getset The command is to return the old value and set the new value ,（ be relative to get and set If executed alone , Send two separate
The order passed ,IO Communication twice , This method only communicates once 【 Save resources 】）

mset Set up multiple key Multiple value
msetnx （ Set up multiple key Corresponding value Guaranteed atomicity ） In the picture below msetnx Set up k3 When it failed

Bitmap （bitmap）

setbit Method , In the corresponding bit Set the value above the bit

bitpos command ：
Find the first byte First of all 1 Position of appearance

Find the second byte to appear 1 The first position

Statistics 1 There are several times in the byte range

bitop Commands can be bitwise value And and or etc

Scene question

1、 The company has a user system , Count the login days of users , And the window is random （ Push forward one week one day , And a week later , Count the number of days users log in ）
One year is set to 400 God , have access to 50 Bytes save the user's login status throughout the year

-2 and -1 For the last two bytes （ Inquire about 300 To the first day 400 God ） How many login times .【 Let users be key Login days are value】
Of course, if you think the number of users is particularly large, you can consider saving one for some users redis, Another part
Save another redis【 notes ：1 Users 50 Bytes , that 20 Users save 1k Space ,20000 The more users need 1MB Space
2000000 Users need 100M Space 】

2、 JD.COM 618 Do activities and give gifts , How many gifts are in stock in the big warehouse ？ Suppose there is 2E user
1、 Classify users （ Divided into zombie users Hot and cold users / Loyal users ）
So we need to do active user statistics ,
What are active users ：
for instance 1 Number -3 Number Continuous login De duplication of repeated login
redis How to do
First, in the 2022 year 1 month 1 Japan id by 1 The user of is logged in to bit Bit 1 Bit setting 1
stay 2022 year 1 month 2 Japan id by 1 and id by 7 Of users logged in at bit position 1 and bit position 7 Set up 1

summary

key Of type type , It is used to determine whether the access method has this type of operation , It can quickly return errors , Can avoid
abnormal .
encoding It can avoid the same type Type, but calculate according to different forms ,
also length attribute , If the data has not changed, you can directly return the length