Long-form notes on software, distributed systems, and the craft of building.

Three Phases of Online Data Movement, Read as Three Invariants

Every online migration diagram I have seen looks the same — three arrows between two boxes — and skips the part that matters: what each phase is actually for. These are my notes after re-reading Stripe's DocDB writeups against the gh-ost and Vitess cutover docs, distilled into three invariants I can graph and gate.