Hash tag usage in redis cluster

        hash tag be used for redis In the cluster . It is realized in key Add a {}, for example test{1}. Use hash tag After that, the client is calculating key Of crc16 when , Only calculate {} Data in the . If not used hash tag, The client will be responsible for the whole key Conduct crc16 Calculation . So let's do that hash tag Use .

    
     

      
 
       
 
        
 
       
 
       
 
        

          127.0.0.1:6380> cluster keyslot user: 
         case 
        
 
       
      
 
       
 
        
 
       
 
       
 
        

          ( 
         integer) 9491 
        
 
       
      
 
       
 
        
 
       
 
       
 
        

          127.0.0.1:6380> cluster keyslot user: 
         case{1} 
        
 
       
      
 
       
 
        
 
       
 
       
 
        

          ( 
         integer) 9842 
        
 
       
      
 
       
 
        
 
       
 
       
 
        

          127.0.0.1:6380> cluster keyslot user:info 
        
 
       
      
 
       
 
        
 
       
 
       
 
        

          ( 
         integer) 15429 
        
 
       
      
 
       
 
        
 
       
 
       
 
        

          127.0.0.1:6380> cluster keyslot user:info{1} 
        
 
       
      
 
       
 
        
 
       
 
       
 
        

          ( 
         integer) 9842 
        
 
       
      
 
       
 
        
 
       
 
       
 
        
 
        
 
       
      
 
       
 
        
 
       
 
       
 
        
 
        
 
       
      
 
       
 
        
 
       
 
       
 
        

           You can see through the above code , Don't use  
         hash tag  Corresponding  
         hash slot Is different , After use, it will correspond to a  
         hash slot in  
        
 
       
     
    
     

  advantage ：

      hash tag The main function is to store a fixed feature data on an instance , Avoid querying instances in the cluster one by one . For example, user information and user order quantity are stored in an instance for subsequent display statistics .

    
     

      
 
       
 
        
 
       
 
       
 
        

           Will the user id by  
         1 The relevant information of is stored in  
         6380 example  
        
 
       
      
 
       
 
        
 
       
 
       
 
        
 
         127.0.0.1:6380> set 
         user:info{ 
         1}  essential information  
        
 
       
      
 
       
 
        
 
       
 
       
 
        

          OK 
        
 
       
      
 
       
 
        
 
       
 
       
 
        
 
         127.0.0.1:6380> set 
         user:order{ 
         1} 
         2 
        
 
       
      
 
       
 
        
 
       
 
       
 
        

          OK 
        
 
       
      
 
       
 
        
 
       
 
       
 
        
 
         127.0.0.1:6380> keys * 
        
 
       
      
 
       
 
        
 
       
 
       
 
        
 
         1) 
         "user:order{1}" 
        
 
       
      
 
       
 
        
 
       
 
       
 
        
 
         2) 
         "user:info{1}" 
        
 
       
     
    
     

shortcoming ：

        It may cause the data to be concentrated in one instance , Cause data skew , For example, the user 1-10000 The data of is stored in an instance .

    
     

      
 
       
 
        
 
       
 
       
 
        

           If only  
         1- 
         10000 Of users have order information , Then it is equivalent to that all information is stored in  
         6380 In this instance  
        
 
       
      
 
       
 
        
 
       
 
       
 
        
 
         127.0.0.1:6380> set 
         user: 
         1 
         :order{ 
         1- 
         10000} 
         2 
        
 
       
      
 
       
 
        
 
       
 
       
 
        

          OK 
        
 
       
      
 
       
 
        
 
       
 
       
 
        
 
         127.0.0.1:6380> set 
         user: 
         2 
         :order{ 
         1- 
         10000} 
         2 
        
 
       
      
 
       
 
        
 
       
 
       
 
        

          OK 
        
 
       
      
 
       
 
        
 
       
 
       
 
        
 
         127.0.0.1:6380> set 
         user: 
         3 
         :order{ 
         1- 
         10000} 
         2 
        
 
       
      
 
       
 
        
 
       
 
       
 
        

          OK