On environment upgrade with trac-admin of Trac 0.13dev I get
File "/lib/python2.5/site-packages/Trac-0.13dev-py2.5.egg/trac/env.py", line 646, in needs_upgrade
File "build/bdist.linux-i686/egg/announcer/api.py", line 493, in environment_needs_upgrade
File "/lib/python2.5/site-packages/Trac-0.13dev-py2.5.egg/trac/db/util.py", line 107, in __getattr__
This applies to all recent versions of Trac, because the rollback method has been removed from read-only connections. db argument to environment_needs_upgrade IEnvironmentSetupParticipant method is such a read-only connection (see T:#10451).
Maybe this is related to other currently open tickets, but then this is rather blurred there, so better have it explicit here.