Another alternative to classic Bloom filter is the cuckoo filter, based on space-efficient variants of cuckoo hashing. In this case, a hash table is constructed, holding neither keys nor values, but short fingerprints (small hashes) of the keys. If looking up the key finds a matching fingerprint, then key is probably in the set. One useful property of cuckoo filters is that they are updatable; entries may be dynamically added (with a small probability of failure due to the hash table being full) and removed.