Redis used_memory_rss is more than the config set 'maxmemory'?

Question

We have Set 120 GB Max Memory in Redis Server.

So in info output used_memory is always less than equal to 120GB but used_memory_rss is ~140GB

Can Someone Please explain the reason of this?

Answer 1

Total used memory includes any memory Redis has used outside of data storage, in particular various buffers and memory used during disk persistence operations such as BGSAVE and AOF rewrites. The maxmemory setting is for the amount of data allowed (and includes some buffers such as client buffers) - not total system memory.

When you reach maxmemory Redis will stop allowing added memory usage through data commands. But it is still free to use memory outside of that to handle it's other duties.