A cuckoo filter is a space-efficient probabilistic data structure that is used to test whether an element is a member of a set, like a Bloom filter does. False positive matches are possible, but false negatives are not – in other words, a query returns either "possibly in set" or "definitely not in set". A cuckoo filter can also delete existing items, which isnot supported by Bloom filters.In addition, for applications that store many items andtarget moderately low false positive rates, cuckoo filters can achievelower space overhead than space-optimized Bloom filters.