Good question! You can't re-key your records but this done is by design. We want the materialized partitions to reside on the same brokers as their sources so t

Good question! You can't re-key your records but this done is by design. We want the materialized partitions to reside on the same brokers as their sources so there is no network overhead for performing the transform, and it occurs on all nodes. So by choosing this design we traded off more CPU for lower latency and less network bandwidth.