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Redis string type
2022-07-06 01:40:00 【Freezing point contract】
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
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