And does every user have their own algorithm?

And could it be made readable to a human?

Take an example like gravity: is there an algorithm for how gravity acts even though it varies per each molecule based on a kajillion other molecules? Of course there is.

I for one haven't worked at FAANG and think it'll be super interesting to read this code, I can't believe software engineers are complaining about a potentially super complex bleeding edge codebase for timeline recommendations / ranking being open sourced. This is going to be great reading material if it ever gets published!

Systems comprised of (or generated by) comprehensible parts can be comprehended, we just often opt not to put in that work. There's a reason model interpretability is such a significant and increasingly-demanded area of expertise.

Or the trained model itself. There are people looking for intentional bias. But the insidiousness of the problem likely arises from unintentional bias. Letting researchers brute force the ranking models with hypotheticals could be a win win.

  ORDER BY timestamp DESC;

I disagree b/c: That's a system. An algorithm is designed, a system will emerge from pieces. An algorithm can be defined, a system's behavior has to be characterized post-hoc. You can characterize a system, but only as a black/gray box. An algorithm has invariants and stateful steps, a system has nearly infinite state and nearly zero meaningful invariants.

still a system that maps inputs and state to outputs and outputs and state updates.

A collection of algorithms is just a bigger algorithm.