Redis learning-SDS Data Type

I started learning about redis today. I wanted to see it directly from the source code. However, I saw a basic tutorial on redis, redis design and implementation (first version).

So I decided to start from here.

 

1. Data Type Definition

 

typedef char *sds;struct sdshdr {    // buf 已占用长度    int len;    // buf 剩余可用长度    int free;    // 实际保存字符串数据的地方    char buf[];};

2.重新计算新的长度

newlen = sdshdr.len + required_len

if newlen < SDS_MAX_PREALLOC:        newlen *= 2    else:        newlen += SDS_MAX_PREALLOC

3. 关于这种分配策略会浪费内存吗？

执行 APPEND 命令的字符串键数量通常并不多， 占用内存的体积通常也不大， 所以这一般并不算什么问题
如果执行 APPEND 操作的键很多， 而字符串的体积又很大的话， 那可能就需要修改 Redis 服务器， 让它定时释放一些字符串键的预分配空间， 从而更有效地使用内存。

Summary

• The redis string is expressedSDSInstead of the C string (\ 0EndChar *).
• Compare the C string,SDSIt has the following features:
  • You can perform length calculation efficiently (Strlen);
  • You can perform the append operation efficiently (Append);
  • Binary Security;
• SDSWill be optimized for the append operation: speed up the append operation and reduce the number of memory allocations, at the cost of occupying more memory, and these memories will not be automatically released.

 

Redis learning-SDS Data Type