Callback executed when there is a redis error.

        :param string fname: Function name that was being called.
        :param type exc_type: Exception type
        :param Exception exc_value: The current exception
        :returns: Default value or raise the current exception

def on_redis_error(self, fname, exc_type, exc_value):
        '''Callback executed when there is a redis error.

        :param string fname: Function name that was being called.
        :param type exc_type: Exception type
        :param Exception exc_value: The current exception
        :returns: Default value or raise the current exception
        '''

        if self.shared_client:
            Storage.storage = None
        else:
            self.storage = None

        if self.context.config.REDIS_STORAGE_IGNORE_ERRORS is True:
            logger.error("[REDIS_STORAGE] %s" % exc_value)
            if fname == '_exists':
                return False
            return None
        else:
            raise exc_value