It's only default behavior. The alternative is for any request that runs more than one query to be inherently but unpredictably unreliable; that is definitely

It's only default behavior. The alternative is for any request that runs more than one query to be inherently but unpredictably unreliable; that is definitely not acceptable. If you're doing something complicated, you're going to have to tread carefully anyway. No default could have handled your situation cleanly. For what it's worth, zope transactions (which Pyramid uses) support combining notions of "transaction" from arbitrary other services and tries to do the right thing for a commit and rollback. I've used this to keep a database and mogilefs in sync, for example.