We want to ensure only-once message processing, but we also want the benefit
of rebalancing. commitOffsets updates all partitions from out of a
connector instance. We want to commit the offset for just the partition
that delivered a message to the iterator, even if several fetchers are
feeding a thread. Perhaps the message metadata contains the partition a msg
came from; could you not just update the offset for that partition if the
property "only.once=true" is sent to the consumer connector?