Redis string type

String type :string

• String yes Redis Most basic types , You can understand that Memcached As like as two peas , One key Corresponding to one value;
• String Type is binary safe , signify Redis Of string Can contain any data . such as jpg Picture or serialized object
• String The type is Redis Basic data types , One Redis Middle string value At most 512M

Common commands

• Add key value pair

  set <key> <value>
  

• obtain key Corresponding value

  get <key>
  

• Will specify value Append to original value At the end of

  append <key> <value>
  

• obtain value The length of

  strlen <key>
  

• Only when key When it doesn't exist key Add

  setnx <key> <value>
  

• take key Increase the value of the number stored in 1, Can only operate on numeric values , If it is empty , The new value added is 1

  incr <key>
  

• take key The number stored in minus 1, Can only operate on numeric values , If it is empty , The new value added is -1

  decr <key>
  

• take key The numerical value stored in the custom step size increases or decreases

  incrby <key> <step>
  decrby <key> <step>
  

The concept of atomic operation

• Atomic operations are operations that are not interrupted by the thread scheduling mechanism , Once this operation begins , It runs until the end , There won't be any context switch （ Switch to another thread ）
• In a single thread , Operations that can be performed in a single instruction can be considered as " Atomic manipulation ", Because interrupts can only occur between instructions
• In multithreading , Can't be used by other processes （ Threads ） The interrupted operation is called atomic operation
• Redis The atomicity of a single command is mainly due to Redis The single thread

String batch operation command

• At the same time for multiple key Set the value

  mset <key1> <value1> <key2> <value2> ...
  

• Get multiple at the same time value

  mget <key1> <key2> ...
  

• Set up multiple value, And key non-existent ( Atomicity : One existence fails )

  msetnx <key1> <value1> <key2> <value2> ...
  

Other commands

• Get substring , From the index start To stop( Left and right closed )

  getrang <key> <start> <stop>
  

• Use... From the specified index location value Covering substring

  setrang <key> <index> <value>
  

• Set the expiration time while setting the key value pair ( Company :s)

  setex <key> <time> <value>
  

• To old change new ( Read original value , And write )

  getset <key> <value>
  

String data structure

• String The data structure of is a simple dynamic string (Simple Dynamic String, abbreviation SDS). Is a string that can be modified , The internal structure is similar to Java Of ArrayList, Reduce the frequent allocation of memory by pre allocating redundant space
• Space actually allocated internally for the current string capacity Generally higher than the actual string length len. When the string length is less than 1M when , Expansion is to double the existing space , If exceeded 1M, When expanding, it will only expand more at one time 1M Space . Note that the maximum string length is 512M