Thank you, good points. I'm just learning about this in real time.

It looks like it does support transactions, but they basically destroy the performance benefits: https://vitess.io/docs/faq/sharding/advanced/can-i-use-vites...

The more I read the more I'm struggling to understand the benefit of a router like this that sits on top of a monolithic SQL, vs a truly distributed DB like cockroach.

Like you I'd love to learn more about the internals of their actual SQL engine, which is just barely touched on in the article. The idea of ripping out the layer of a SQL interpreter that does just enough to route it to a real server tickles my brain in the same way as when I learned how node.js ripped the js interpreter out of a browser.