ZODB 3 provides limited support for subtransactions. Subtransactions are nested to one level. There are top-level transactions and subtransactions. When a transaction is committed, a flag is passed indicating whether it is a subtransaction or a top-level transaction. Consider the following exampler commit calls:
commit()
A regular top-level transaction is committed.
commit(1)
A subtransaction is committed. There is now one subtransaction of the current top-level transaction.
commit(1)
A subtransaction is committed. There are now two subtransactions of the current top-level transaction.
abort(1)
A subtransaction is aborted. There are still two subtransactions of the current top-level transaction; work done since the last commit(1) call is discarded.
commit()
We now commit a top-level transaction. The work done in the previous two subtransactions plus work done since the last abort(1) call is saved.
commit(1)
A subtransaction is committed. There is now one subtransaction of the current top-level transaction.
commit(1)
A subtransaction is committed. There are now two subtransactions of the current top-level transaction.
abort()
We now abort a top-level transaction. We discard the work done in the previous two subtransactions plus work done since the last commit(1) call.