Large perfect hash tables have to store an awful lot of information. I don't remember quite how it's done but it's not a free lunch. The hash function itself

Large perfect hash tables have to store an awful lot of information. I don't remember quite how it's done but it's not a free lunch. The hash function itself has a size that grows with the total size of all the keys. I don't know offhand how many rehashes you need to get 98% occupancy with cuckoo hashing. There may be ways to optimize it by sharding the table into smaller ones. I'll re-read the wikipedia article when I get a chance. It's a fun algorithm and I've sometimes looked for places to use it.