Introduction and use of redis

redis summary
redis It's a non relational database , The key value database deployed in the slave , Its value There are five types , Respectively string,set,hash,list,zset
STRING： You can store strings , Integer or floating point , You can operate on the whole string or strings in the string , When it is an integer or floating-point number , Self increase or self decrease operation can be carried out

LIST： Main storage list . Press or eject both ends , You can trim multiple elements , Keep only the elements in one range

SET ： You can add, get, and remove individual elements , Calculate and hand in , and , Difference set , Get elements randomly from the collection

HASH： You can add, get, and remove individual elements , Check if the element exists , Get all key value pairs

ZSET： Add get delete element , Get the element according to the score range or member , Calculate the rank of a key
The underlying implementation of data structure
string:
struct sdshdr{
int len;// Length of occupied space
int free;// Length of remaining space
char buf[];// Data space
}
Compared to calling directly c The advantage of string is that it can directly save the length without traversal . In addition, it can also reduce the problem of buffer overflow , Because the remaining length will be checked before use .

list：
Double linked list , But more about it

typedef struct listNode{
    

struct listNode *prev;

struct listNode * next;

void * value;

}

hash:

typedef struct dictht {
    

// Hash table array 

dictEntry **table;

// Hash table size 

unsigned long size;

// Hash table size mask , Used to calculate index values 

unsigned long sizemask;

// The number of existing nodes in the hash table 

unsigned long used;

}

typeof struct dictEntry{
    

// key 

void *key;

// value 
// Different key values may correspond to different types ,
// Therefore use union To solve this problem 
union{
    

void *val;

uint64_tu64;

int64_ts64;

}

struct dictEntry *next;

}

When hash When the conflict , Using zippers to resolve conflicts
zset：
The bottom layer is realized by jumping table , It can be used to replace binary balanced tree

Skip list （skiplist） Is an ordered data structure , It maintains multiple pointers to other nodes in each node , So as to achieve the purpose of quickly finding access nodes . The jump table is a kind of randomized data , A jump table stores elements in a hierarchical linked list in an orderly manner , Efficiency is as good as the balance tree —— lookup 、 Delete 、 Add and other operations can be done in O（logn） Finish... In the expected time .

// Specific implementation of node 
typedef struct zskiplistNode{
    

// layer 

struct zskiplistLevel{
    

// Forward pointer 

struct zskiplistNode *forward;

// span 

unsigned int span;

} level[];

// Back pointer 

struct zskiplistNode *backward;

// The score is 

double score;

// member object 

robj *obj;

}

typedef struct zskiplist {
    

// Header node and footer node 

structz skiplistNode *header,*tail;

// The number of nodes in the table 

unsigned long length;

// The number of layers of the node with the largest number of layers in the table 

int level;

}zskiplist;

Friends who don't know about it can see the following post
Skip List– Jump watch （ There is no one of the most detailed jump table articles in the whole network ）
set：

typedef struct intset{
    

// Encoding mode int16_t、int32_t、int64_t

uint32_t enconding;

//  Number of elements contained in the collection 

uint32_t length;

// Array to hold elements 

int8_t contents[];

}

intset yes Redis One of the memory data structures , And before sds、 skiplist、dict、adlist
And other general data , It is Redis Peculiar , Used to implement Redis Of Set structure （ When the element is small and of numeric type ）, Its characteristics are ：

Element type can only be numeric . There are three types of elements ：int16_t、int32_t、int64_t. The elements are in order , Do not repeat .
intset and sds equally , Memory is continuous , It's like an array .