id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
19707	TransactionMiddleware leaks transaction state	Anssi Kääriäinen	nobody	"TransactionMiddleware process_exception and process_response are written in a style that will leak transaction state on error. process_response for example:
{{{
        if transaction.is_managed():
            if transaction.is_dirty():
                transaction.commit()
            transaction.leave_transaction_management()
}}}

now, what happens if transaction.commit() throws an error? transaction.leave_transaction_management() is never called, and the connection's transaction_state leaks an ""managed"" entry.

This can cause a ""funny"" situation where SessionMiddleware doesn't commit transactions if the SessionMiddleware is above TransactionMiddleware in the middleware stack. This is user visible in that logins do nothing - they don't give any errors, but they don't log in either.

A simple test-project attached. You need to run this under PostgreSQL so that deferred foreign keys can cause an error on commit(). And, you need to use runserver --nothreading as otherwise every request gets a new thread and a new connection with clear transaction state.

Run syncdb and then runserver --nothreading. Go to localhost:8000/view/, then go to localhost:8000/admin/ and try to log in. You can also add from django.db import connection; print connection.transaction_state to process_response to see better what happens.

I have hit this same issue under apache + mod_wsgi so this doesn't happen only in development server without threading.

The bug is present at least in versions 1.4+ of Django. I am marking this as release blocker as this is a crashing bug (logins are impossible when condition hit), and I plan to backpatch this to 1.4-master.

The fix should also be easy: add try-finally to process_response/process_exception."	Bug	closed	Database layer (models, ORM)	1.4	Release blocker	fixed			Accepted	0	0	0	1	0	0