Comment 1 for bug 132485

You probably also need an rollback_prepared() for the case where some other resource fails the first phase of the commit and you want to abort the transaction.

The other form this API could take up is for store.commit() and store.rollback() to perform the second phase of a commit if prepare() was called, and make prepare() a no-op for backends that do not support two-phase commit. This is essentially how Zope transaction data managers that don't support two-phase commit are implemented.