used_memory_rss: Number of bytes that Redis allocated as seen by the operating system (a.k.a resident set size). This is the number reported by tools such as top(1) and ps(1)used_memory: total number of bytes allocated by Redis using its allocator (either standard libc, jemalloc, or an alternative allocator such as tcmallocIf I'm reading this correctly, the rss version shows the whole size of the program (external) and the regular is internal to redis (it doesn't know the size if the program that is running itself)