redis和memcached是不是存储多少空间就占多少内存？

Question

这些内存数据库都是把数据放到内存里，作为缓存的话，是不是存储多少内容就占用多少内存呢？

比如我的Linux服务器是2G内存的，那使用他们作为缓存数据库，就不能缓存超过2G的内容呢？

Answer 1

It’s not about how much memory you save.

memcached’s caching mechanism
memcached uses the Slab Allocation memory allocation mechanism. You can read this article Memcached’s data storage method
This mechanism has a disadvantage. It divides the allocated memory into chunks (chuck) of a specific length, such as : Storing 70-byte data into 88-byte blocks results in a waste of 18 bytes

Memory allocation process

Redis will be added if needed or later.

Answer 2

Yes. Because they are memory-based databases.

Although it can be transformed to use the disk to cache part of the data, doing so will lose its own meaning.