I wrote some unittests to investigate some odd transaction behavior i noticed while doing unittests of integrating non sub transaction aware objects, and to insure proper txn behavior. these tests test the transaction system independent of the rest of the zodb and test failure modes as well. i've found a few bugs. 1. TM.py ignores calls to tpc_abort. this i believe is the likely cause of most of the rdbms integration problems that are referenced above as TM.py generally forms the integration point between db adapters and zope's transaction framework. if an error occurs in the two-phase-commit protocol, the database adapter will never recieve a finish/commit or abort message, and will therefore (due to how TM works) never be able to register again for a zope transaction. 2. A Non Sub Transaction aware object (including any TM derived object) that participates in a sub-transaction will recieve a tpc_finish message (which for TM derivatives calls _finish) as part of the subtransaction commit process. this means that if the outer transaction is latter aborted, there will be a loss data integrity. 3. As part of the commit process for a transaction involving subtransactions, any objects registered since the last subtransaction commit will be involved in an implicit subtransaction commit. if an error occurs during this implicit subtransaction, none of the objects registered previously to the last explicit subtransaction commit will recieve any messages. i'm not sure totally sure this is a bug since any calls to explicitly begin a new transaction should abort the objects that haven't recieved any transaction messages. in a zope setting this is done automatically, however standalone users should be aware of this. i've posted a modified TM.py to my zope.org member page that contains fixes/workarounds for problems 1 and 2. http://www.zope.org/Members/k_vertigo/ShortStories/Transaction/ in addition the unittests i've been using are posted there as well. i'll commit these changes to TM.py latter today, but have posted the above to zope.org for those who don't want to immediately upgrade. actual fixes for problems 2 and 3 i'll leave to ZC. if you're using a rdbms with zope, i would recommend installing the modified TM.py in replace of the exiting TM.py at lib/python/Shared/DC/ZRDB/TM.py. i would appreciate any feedback from rdbms users who were previously experiencing problems. if this does not solve your problem, and you believe its the fault of the transaction system, please email me. i don't use an rdbms with zope, but i'm happy to further investigate. cheers kapil thangavelu