Major Description
With KIP-74, we now have a good way to limit the size of fetch responses, but it may still be difficult for users to control overall memory since the consumer will send fetches in parallel to all the brokers which own partitions that it is subscribed to. To give users finer control, it might make sense to add a `max.in.flight.fetches` setting to limit the total number of concurrent fetches at any time. This would require a KIP since it's a new configuration.
