My understanding from 2012 paper was that it doesn't support nested transactions, even at the storage layer.
Can anybody provide insider-knowledge if it was even a requested feature from Google devs internally?
> Overcoming this limitation requires supporting reading the uncommitted results within an active transaction. While we have seen comparatively little demand for this feature internally, supporting such semantics improves compatibility with other SQL systems and their ecosystems and is on our long-term radar.
No internal demand, but on "long-term radar".