> Binary search beats SQLite... For a pure ID lookup, you're paying for machinery you're not using.

You'll likely end up quite a chump if you follow this logic.

sqlite has pretty strong durability and consistency mechanism that their toy disk binary search doesn't have.

(And it is just a toy. It waves away the maintenance of the index, for god's sake, which is almost the entire issue with indexes!)

Typically, people need to change things over time as well, without losing all their data, so backwards compatibility and other aspects of flexibility that sqlite has are likely to matter too.

I think once you move beyond a single file read/written atomically, you might as well go straight to sqlite (or other db) rather than write your own really crappy db.