Set of redis data structure

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brief introduction

Reids Of set It's a collection type , You can save multiple string elements , Elements in a collection cannot be repeated , And the elements in the set are also unordered , Cannot get elements in a collection by subscript , These characteristics are related to java Of set Very similar .

data structure

Redis Of set The bottom layer uses intset and hashtable Two data structures are used to store data , among intset It can be understood as a special array , and hashtable It's an ordinary hash table .

Set Underlying storage intset and hashtable Code conversion exists , Use intset Storage must meet the following two conditions , Otherwise use hashtable, The conditions are as follows ：

• 1. All elements saved by the combined object are integer values
• 2. The collection object holds no more elements than 512 individual

hashtable data structure

hashtable The data structure is the same as that in the previous chapter Hash The structure in is basically the same , This chapter will not repeat the description .

intSet data structure

explain ：

• encoding:contents The type of data saved , The default type is int16_t.
• contents: Actual content array
• length：contents The number of elements

Basic commands

sadd Additive elements

Basic grammar

sadd key value1...valuen

Example

scard Get the number of members of the collection

Basic grammar

scard key

Example

sdiff Get the difference between the set and the set

Basic grammar

sdiff key1 key2

Example

sinter Get the intersection of a set and a set

Basic grammar

sinter key1 key2

Example

sismember Judge member Is the element a collection key Members of

Basic grammar

sismember key member

Example

smembers Get all members of the collection

Basic grammar

smembers key

Example

sunion Get the union of all the given sets

Basic grammar

sunion key1 key2

Example

srem Remove one or more elements

Basic grammar

srem key member

Example

sscan Elements in iteration set

Basic grammar

sscan key cursor [match pattern] count

explain ：

• cursor: The cursor , from 0 Start
• pattern : Matching mode
• count： Specifies how many elements to return from the dataset , The default value is 10.

Example

sscan mset 0 match j*

Application scenarios

• Counting cell phones App Number of new users per day

key With user:id And the date of the day , for example user:id:20200803; value by Set aggregate , Record the users logged in on that day ID.

• Blog mutual friend

  adopt set Get the intersection of multiple sets .

• Webpage UV The statistics of

Count the number of times a user visits a web page every day , A user's multiple visits in a day can only be counted as one .

matters needing attention

use Set For some large sets of related accurate statistics , Very inefficient , High memory overhead , Try to avoid in the production environment .

summary

This chapter explains Redis Data structure of Set, We need to pay attention to redis Of set Usage scenarios for aggregation operations , If you have any questions, please feel free to give feedback .