Fixed #19707 -- Reset transaction state after requests

django/middleware/transaction.py

@@ -15,6 +15,10 @@ class TransactionMiddleware(object):
     def process_exception(self, request, exception):
         """Rolls back the database and leaves transaction management"""
         if transaction.is_dirty():
+            # This rollback might fail because of network failure for example.
+            # If rollback isn't possible it is impossible to clean the
+            # connection's state. So leave the connection in dirty state and
+            # let request_finished signal deal with cleaning the connection.
             transaction.rollback()
         transaction.leave_transaction_management()
 
@@ -22,6 +26,21 @@ class TransactionMiddleware(object):
         """Commits and leaves transaction management."""
         if transaction.is_managed():
             if transaction.is_dirty():
-                transaction.commit()
+                # Note: it is possible that the commit fails. If the reason is
+                # closed connection or some similar reason, then there is
+                # little hope to proceed nicely. However, in some cases (
+                # deferred foreign key checks for exampl) it is still possible
+                # to rollback().
+                try:
+                    transaction.commit()
+                except Exception:
+                    # If the rollback fails, the transaction state will be
+                    # messed up. It doesn't matter, the connection will be set
+                    # to clean state after the request finishes. And, we can't
+                    # clean the state here properly even if we wanted to, the
+                    # connection is in transaction but we can't rollback...
+                    transaction.rollback()
+                    transaction.leave_transaction_management()
+                    raise
             transaction.leave_transaction_management()
         return response