CF.RESERVE key capacity [BUCKETSIZE bucketsize] [MAXITERATIONS maxiterations] [EXPANSION expansion]
Create a Cuckoo Filter as
key with a single sub-filter for the initial amount
capacity for items. Because of how Cuckoo Filters work, the filter is
likely to declare itself full before
capacity is reached and therefore fill
rate will likely never reach 100%. The fill rate can be improved by using a
bucketsize at the cost of a higher error rate.
When the filter self-declare itself
full, it will auto-expand by generating
additional sub-filters at the cost of reduced performance and increased error
rate. The new sub-filter is created with size of the previous sub-filter
Like bucket size, additional sub-filters grow the error rate linearly.
The size of the new sub-filter is the size of the last sub-filter multiplied by
The minimal false positive error rate is 2/255 ≈ 0.78% when bucket size of 1 is used. Larger buckets increase the error rate linearly (for example, a bucket size of 3 yields a 2.35% error rate) but improve the fill rate of the filter.
maxiterations dictates the number of attempts to find a slot for the incoming
fingerprint. Once the filter gets full, high
maxIterations value will slow
Unused capacity in prior sub-filters is automatically used when possible. The filter can grow up to 32 times.
- key: The key under which the filter is found.
- capacity: Estimated capacity for the filter. Capacity is rounded to the
2^nnumber. The filter will likely not fill up to 100% of it's capacity. Make sure to reserve extra capacity if you want to avoid expansions.
- bucketsize: Number of items in each bucket. A higher bucket size value improves the fill rate but also causes a higher error rate and slightly slower performance. The default value is 2.
- maxiterations: Number of attempts to swap items between buckets before declaring filter as full and creating an additional filter. A low value is better for performance and a higher number is better for filter fill rate. The default value is 20.
- expansion: When a new filter is created, its size is the size of the current filter multiplied by
expansion. Expansion is rounded to the next
2^nnumber. The default value is 1.
redis> CF.RESERVE cf 1000 OK
redis> CF.RESERVE cf 1000 (error) ERR item exists
redis> CF.RESERVE cf_params 1000 BUCKETSIZE 8 MAXITERATIONS 20 EXPANSION 2 OK