Re: ACID guarantees

It doesn't have a notion of atomically batching multiple statements, i.e. transaction. But beyond that, it's a single file database, which can only have a single process (learndb instance) that is operating on the database (file). So you get consistency and isolation via being a single connection database. Durability, you get to the extent that the file system is durable. So it's somewhere on the ACIDity spectrum.

Re: Query planning/optimization

I haven't implemented this; but I've considered where the optimization could module sit: The parser spits out an AST. This or a derived intermediate representation could be optimized,i.e. the AST could be rewritten or nodes deleted, before the VM executes the AST.