No modern DB uses mmap because it's unreliable and hard to tune for performance. A custom cache manager will always perform better than mmap provided by the ke

No modern DB uses mmap because it's unreliable and hard to tune for performance. A custom cache manager will always perform better than mmap provided by the kernel. The problem is you haven't explained how the overhead of a DB is too much. Sure, it sounds like a lot of work for your servers and the DB compared to reading from a hashmap. Where I work right now we fire around 1.5B queries a day... to Mongo.