[munk-a]

Save points, with proper management of them, seem to match a conceptual nested transaction as far as I've seen. We've got a test bed connection manager that mocks savepoint creation, rollback and committal into transaction management functions so doing something like beginTransaction && beginTransaction works fine.

[atombender]

There may be some semantic nuances. Savepoints aren't real transactions, so they "inherit" the locks of the parent transaction, for example. But it might not matter in practice in the context of tests.