Critical Description
Streaming receivers are currently scheduled by the underlying Spark scheduler in the same way as other tasks. Will help performance if we added a knob to control receiver scheduling. In most cases, even distribution of receivers among workers should yield best results. In some cases, dense scheduling (e.g, all receivers on one node) may perform better. Maybe support for a new configuration parameter spark.receiver.scheduling.mode (or some such) would help. With 'default' as the current scheduling scheme and 'round-robin' for even distribution among workers (and potentially a third mode for 'dense' scheduling).
