Redis list

Redis list (List)

Introduce

• Single bond multi value
• Redis List is a simple list of strings , Sort by insertion order . You can add an element to the head of the list （ On the left ） Or tail （ On the right ）
• Its bottom layer is actually a two-way linked list , High performance on both ends , The performance of the nodes in the middle of the index subscript operation will be poor

Common commands

• Insert one or more values from the left

  lpush <key> <value1> <value2> ...
  

• Insert one or more values from the right

  rpush <key> <value1> <value2> ...
  

• Pop up a value from the left ( The value will be deleted )

  lpop <key>
  

• Pop up a value from the right ( The value will be deleted )

  rpop <key>
  

• From the list key1 A value pops up on the right and is inserted into key2 On the left

  rpoplpush <key1> <key2>
  

• Get elements in batches according to the index (-1 Represents the last element )

  lrange <key> <start> <stop>
  

• Get a single element according to the index ( From left to right )

  lindex <key> <index>
  

• Get list length

  llen <key>
  

• stay value Insert element before target

  linsert <key> before <value> <target>
  

• Delete from the left n The values are value The elements of

  lrem <key> <n> <value>
  

• Index the list as index Replace the value of with value

  lset <key> <index> <value>
  

The underlying data structure of the list

• List The data structure of is fast linked list quickList
• First, in the case of fewer list elements will use a block of continuous memory storage , This structure is ziplist, That is, compressed list ( It's like a sequence table ), It stores all the elements next to each other , Allocated is a continuous block of memory , When there is a large amount of data, it will be changed to quicklist, Because ordinary linked list needs too much additional pointer space , It's a waste of space . For example, what's in this list is just int Data of type , Two additional pointers are required for the structure prev and next
• Redis Linking lists and ziplist Combined to form quicklist, That is to say, multiple ziplist Use two-way pointer string to use . This not only satisfies the fast insertion and deletion performance , There will not be too much space redundancy