Difference between redis hash and string

Similarities and differences

Suppose we want to save the computer information of a school redis

• Use string method ：KEY Prefix computer information + School name + Device identifier ,value For specific information json
• Use hash Methods ：KEY Prefix computer information + School name , In hash key Subdivision Device identifier

The same thing ：

First, they have many commands with similar effects , such as set and hset,mset and hmset wait
In most cases, scenarios that use string storage use hash It can also be realized .

Difference

Their storage structure determines that they have some essential differences

Use hash The advantages of hashing

• Use hash Data can be placed in the same place for easy management , Instead of having to put the data in the whole database with a string , And it can also avoid misoperation .
• Use hash Hashing can not only reduce the number of keys created, but also avoid key name conflicts .
• Use hash Hashing saves more memory than using string keys . Because create in the database key All have database attached management information （ For example, the type of key , Last visit time, etc ）, therefore keys The more , The more memory the server consumes in storing additional management information , At the same time, it is spent in the management database key Of cu’p The more you will be . and redis Ability will be right hash Do some low-level optimization for your storage , Less memory consumption .

Use strings in specific cases

• Use expiration function
  because redis The expiration function of can only operate on the key, not the hash key field To operate .
  Commands for binary storage
• because redis At present, only string keys are supported setbit,getbit,bitop And other binary related command operations .

So use strings and hash If it's ok , Use as much as possible hash
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Big key problem
hash Many middle elements will cause big key.
But it seems that reading a single does not affect .
because redis Single thread , But if getall Or when it's deleted It will cause obstruction ！