On 18/01/2008, M.-A. Lemburg <[EMAIL PROTECTED]> wrote: > While this would seem desirable, it is not how the Zope TM > works. > > Phase 1 is implemented by doing a vote on the success > of the transaction. Phase 2 then finishes or aborts the transaction > depending on the vote. > > If something fails in phase 2, there's no guarantee that partial > commits can be undone. > > The .commit()/.rollback() calls on the database interface would > be implemented in the phase 2 part. > > To avoid your scenario, the ZODB would have to detect the conflict > during phase 1 (ie. the voting phase).
Looking at the IDataManager API, it looks like it looks like the correct way to implement two phase commit would be: 1. if tpc_begin() is called, note that two-phase commit is being used. 2. in commit(), simply prepare the transaction if the two-phase commit flag is set, rather than actually committing. If this fails, the transaction obviously fails. 3. make tpc_vote() a no-op. 4. tpc_finish() commits the prepared transaction 5. abort() and tpc_abort() roll back the prepared transaction (if one was prepared). James. _______________________________________________ DB-SIG maillist - DB-SIG@python.org http://mail.python.org/mailman/listinfo/db-sig
