Working with Cuckoo Filters

1. Adding Elements to Filter

Command	Returns
`CF.ADD key item`	`1` on success
`CF.ADDNX key item`	`1` if not previously present, `0` if existed

Command	Returns
`CF.EXISTS key item`	`1` probably present, `0` definitely absent
`CF.MEXISTS key i1 i2 ...`	Per-item array

Command	Notes
`CF.DEL key item`	Removes one occurrence; may produce false negatives if item never inserted
`CF.COUNT key item`	Approximate occurrence count

Command	Description
`CF.INSERTNX key [CAPACITY c] [NOCREATE] ITEMS i ...`	Add only missing items

CF.RESERVE seen 1000000 BUCKETSIZE 2 MAXITERATIONS 20 EXPANSION 1

Param	Detail
capacity	Expected items
BUCKETSIZE	Items per bucket (1–4)
MAXITERATIONS	Insertion eviction attempts
EXPANSION	New sub-filter growth

Command	Returns
`CF.INFO key`	Size, buckets, capacity, items

Property	Detail
Supports DEL	Yes, unlike Bloom
Caveat	Deleting unknown items can cause false negatives on real items

Tradeoff	Detail
Higher capacity	More memory; better insert success rate
BUCKETSIZE 4	Better load factor, slower

Use Case	Detail
URL crawler dedup	Massive cardinality, occasional removals
Already-sent notifications	Bounded retention with DEL