> - Sub-transactions would have the same isolation properties relative to each other and their parent
> transaction as concurrent transactions have to each other and the state of the database (outside of
> any transaction) ... yes, sub-transactions could deadlock.
>
> I would expect sub-transactions to see everything their parent transaction(s) did up until the
> spawning point, and I would expect parent transactions to see everything their sub-transactions
> have done once they've committed (rejoining the parent, thus acting as if the parent has performed
> those actions directly)

... which would brake the basic behaviour of snapshot transactions.
The same row read twice could return different values if the sub-transaction
updated that row and committed in between.

Ivan