Skizze - A probabilistic data structure service and storage

https://github.com/skizzehq/skizze

Solve frequency and cardinality queries over a data stream in near O(1) time, with minimal memory footprint. Here at Immobiliare.it we serve a large number of HTTP requests per second, and this service might allow us to compute efficiently Top-K referrers, Top-K classes of IP, number of unique users logged in and so on with minimal storage requirements.