Process a request.

def process_request(self, request):
        """Process a request."""
        batcher = PrioritizedBatcher.global_instance()
        if batcher.is_started:
            # This can happen in old-style middleware if consequent middleware
            # raises exception and thus `process_response` is not called.
            # Described under 3rd point of differences:
            # https://docs.djangoproject.com/en/1.11/topics/http/middleware/#upgrading-pre-django-1-10-style-middleware
            batcher.rollback()
            logger.warning(
                "Uncommited batcher transaction from previous request was rollbacked."
            )

        batcher.start()