Hey Nican! Thanks for the feedback. It wasn’t clear from the blog post, but as the sibling poster points out, the system has full eventual consistency: it behaves like a replica, but it replicates a whole cluster of MySQL instances simultaneously (i.e. your full PlanetScale database). Because of this design, we never lock or affect the performance of writes to the main database.

As for predictability, we’re working on some interesting optimizations that allow similar queries to reuse the internal state of each other, so the system becomes more efficient the more queries it’s caching. Stay tuned!