What is the underlying principle of string storage in R…

Redis stores strings by storing them in byte arrays. Redis uses a data structure called sds (simple dynamic string) to represent strings in the C programming language. In C, sds is defined by the following structure.

struct sdshdr {
    int len; // 字符串的长度
    int free; // 字符串中未使用的字节空间
    char buf[]; // 字节空间，用于存储字符串
};

Instead of using null-terminated strings in C language, SDS represents strings by storing the bytes in the buf array. This effectively prevents buffer overflow issues.

There are several important features of SDS.

1. Dynamic adjustment: sds can dynamically allocate or release memory based on the length of strings.
2. Pre-allocation: SDS will allocate a certain amount of additional space in advance to avoid frequent memory allocation operations when expanding strings.
3. Buffer overlap: SDS avoids performance issues with string concatenation by adding the new string to the end of the existing string instead of creating a new string.

This storage method makes Redis’s string data structure very efficient, particularly suitable for handling a large number of string operations.