The cache2k clock-pro algorithm runs with fixed sizes of data structures that yielded the best results over all benchmark trace I could get a hold on, see: https://cruftex.net/2016/05/09/Java-Caching-Benchmarks-2016-Part-2.html

Nevertheless there are some patterns that result in worse hit rates than LRU.

Ben is experimenting with some adaptions, that look interesting. See: ben-manes/caffeine#106