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This article introduces the knowledge of "how to use hash instead of string to save memory". In the operation of practical cases, many people will encounter such a dilemma, so let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!

Https://blog.csdn.net/javarrr/article/details/93380853

When a hash object can meet both of the following conditions, the hash object uses ziplist encoding:

The string length of the keys and values of all key-value pairs saved by the hash object is less than 64 bytes.

The number of key-value pairs saved by hash objects is less than 512; the underlying layer of ziplist-encoded data is to use compressed lists as the underlying data structure.

Https://www.jianshu.com/p/dee0f1edc4e4

The reason for provincial memory is that when you create a new hash object, it starts with ziplist (also known as small hash). This ziplist is not really a hash table, but ziplist can save some of the metadata storage overhead needed by hash itself compared to a normal hash implementation. Although the addition, deletion and lookup of ziplist are all O (n), the number of field of general objects is not too large. So using ziplist is also fast, that is to say, the average of adding and deleting is still O (1). If the size of field or value exceeds a certain limit, redis will automatically replace ziplist with the normal hash implementation internally, which can be controlled by specifying the hash-zipmap-max-entries parameter in the configuration file. When hash-zipmap-max-entries is set to 1000, the performance is better, and the HSET command will cause CPU consumption to become very large after 1000.

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