Great lecture so far. Haven't had the time to watch the whole lecture, but one thing I want to mention is that there are techniques to improve the buffer manager performance as for instance described here by Goetz Graefe: http://www.vldb.org/pvldb/vol8/p37-graefe.pdf

I've implemented an even simpler solution for my Open Source Data Store (https://sirix.io) in that each page stores a number of references, which are itself lightweight pointer objects (in Java) and it simply stores an in-memory reference as well as a pointer to the location to fetch it from disk/a flash drive. If the buffer manager has these Objects as keys on eviction we can simply null the reference to the in-memory page instance.