Petahashes

Definition: through a certain hash algorithm (typically MD5, SHA-1, etc.), a long piece of data is mapped to a short piece of data, which is the hash value of big data. He has such a characteristic that he is the only one. Once big data changes, even a small change, his hash value will also change

on the other hand, since it is DNA, it ensures that the hash values of no two data are exactly the same

the function of hash value: hash value, that is, hash value, is a group of binary values obtained by encrypting the contents of the file. It is mainly used for file verification or signature. Because of this feature, it is often used to determine whether two files are the same

for example, to download a file from the network, just compare the original hash value of the file with the hash value of the downloaded file. If the hash value is the same, it means that the two files are exactly the same, and the file is not damaged ring the download process. If not, it indicates that the downloaded file is different from the original file, and the file is damaged ring the download process

extended data:

hash value is a method to create small digital "fingerprint" from any kind of data. Hash value compresses the message or data into a summary, which makes the data smaller and the data format fixed. This function scrambles the data and creates a new fingerprint called hash values, hash codes, hash sums, or hashes

hash value is usually represented by a short string of random letters and numbers. Good hashes rarely have hash conflicts in the input field. In hash table and data processing, it will be more difficult to find database records to distinguish data without suppressing conflicts

typical hash values have very large domains, such as SHA-2, which can accept (2-1) / 8 byte strings. At the same time, the hash value must have a limited range, such as a fixed length bit string. In some cases, the hash value can be designed to have the same size of the definition field and the injectivity between the value fields. The hash value must be irreversible

A hash with a few fields (where few means up to one hundred or so) is stored in a way that takes very little space, so you can store millions of objects in a small Redis instance.

While Hashes are used mainly to represent objects, they are capable of storing many elements, so you can use Hashes for many other tasks as well.

Every hash can store up to 2^32- 1 field-value pairs (more than 4 billion).

摘自Redis官网的Data type章节，意思是内存允许的情况下，可以存超过40亿数据

网页链接