[uzerfcwn]

It seems like the author had some very specific read and write pattern in mind when they designed for performance, but it's never explicitly stated. The problem setting only stated that "reads are more common than writes", but that's not really saying much when discussing performance. For example, a HTML server commonly has a small set of items that are most frequently read, and successive reads are not very strongly dependent. On the other hand, a PIM system may often get iterative reads correlated on some fuzzy search filter, which will be slow and thrash cache pretty badly if the system is optimized for different access patterns.

When designing software, you first need to nail down the requirements, which I didn't really find in TFA.