[jdoliner]

> RethinkDB has no access to the structure of the source in order to analyze it statically and work out an optimal I/O read plan.

Actually this isn't true. One of the really cool things about RethinkDB is that despite the fact that queries are specified in third party scripting languages they actually get compiled to an intermediate language that RethinkDB can understand.

That being said AFAIK RethinkDB doesn't optimize selects the way columnar databases do. I believe it can only read from disk at a per document granularity. But it does have the ability to optimize this in the future.