Redis offeres alot more then just a key value store. The fuss is the data structures it provides. And just using a hash map in memory isn't sufficient. You'll

Redis offeres alot more then just a key value store. The fuss is the data structures it provides. And just using a hash map in memory isn't sufficient. You'll have unbounded growth. You need a max size and need to evict. Then you want to do that efficiently so your not wasting space on useless keys...