Currently, the Coordinator waits for backends rather than proactively cancelling them in the case of hitting EOS. There's a tangled mess that makes it tricky to proactively cancel the backends related to how Coordinator::ComputeQuerySummary() works – we can't update the summary until the profiles are no longer changing (which also makes sense given that we want the exec summary to be consistent with the final profile). But we current tie together the FIS status and the profile, and cancellation of backends causes the FIS to return CANCELLED, which then means that the remaining FIS on that backend won't produce a final profile.
With the rework of the protocol for
IMPALA-2990 we should make it possible to sort this out such that a final profile can be requested regardless of how a FIS ends execution.
This also relates to IMPALA-5783.