The Four Pieces of Pie

All of the major database systems are multi-threaded. A better B-tree affects only 10% of the path length, meaning it's not worth doing. If you have a database system and let's say it implements data in main memory, that gets rid of the buffer pool. But if you continue to be multi- threaded, do a right-ahead log and do dynamic record level locking then those three slices of the pie are still there.