Is There a Requirement for a Hash Table?

The hash table must fit in memory, right? If you don't have enough ram, this was the whole bit cask. Range queries are going to be inefficient if you have to look up each individual key. The width of this thing is alrady smaller. It's almost like filling a glass of water, pouring it out, filling it back up. And then there might be an additional operations that we haven't got into yet.