Eighteen lessons on how the database actually reads your rows, combines your tables, and decides what to do with your indexes.
There is a moment, somewhere between your first slow query and your hundredth, when you realise the database is not a black box — it is a machine with parts, and those parts have names. This is a short course in those names: Seq Scan, Bitmap Heap Scan, Nested Loop, and the quieter pieces around them.
Each lesson is a single page, a fixed-length walk through the operator, rendered with moving pictures rather than prose alone. The aim is the opposite of exhaustive: to give you the mental model, and a few source-code breadcrumbs to follow when you want more.