I have been considering to implement Bε tree indexes in open source project. As far as I understand PerconaFT key value store uses them as a base for their Fractal Indexes, and they claim that they use several US patents - No. 8,185,551 and No. 8,489,638. I am not a lawyer, so I have a question does it mean that nobody else can practically implement Bε Tree based indexes in their software product?
This question seems more suited for a legal advice forum, or perhaps even for hired legal counsel. IP law is a rather convoluted and tricky subject, and you may want to get official legal advice before proceeding.
I do not know if you will find anyone on here who is willing to tell you that you definitively can or cannot use patented software in an open-source project.