Cuckoo Filter
A probabilistic membership structure that can rule out absent items and report possible presence, while supporting deletion more naturally than a conventional Bloom filter.
A Cuckoo filter stores short fingerprints rather than full keys. If a queried fingerprint is absent from its candidate buckets, the item is definitely not represented; a hit still needs confirmation because false positives are possible.
Deletion is a natural part of the design, but high load factors make insertion harder and fingerprint length controls the false-positive rate. In large indexes or cache layers it can act as a cheap membership check before an expensive remote lookup.