The benchmark at https://github.com/facebook/rocksdb/wiki/Performance-Benchma... states that for LevelDB, "in 24 hours it inserted only 2 million key-values", and that "each key is of size 10 bytes, each value is of size 800 bytes".

I might be missing something, but that took just a few minutes on my ~2 year old desktop machine. Sample code: https://gist.github.com/wbolster/7487225