Today when canceling a task we broadcast ban/unban requests to all nodes
in the cluster. This strategy does not scale well for hierarchical
cancellation. With this change, we will track outstanding child requests
and broadcast the cancellation to only nodes that have outstanding child
tasks. This change also prevents a parent task from sending child
requests once it got canceled.
Relates #50990
Supersedes #51157
Co-authored-by: Igor Motov <igor@motovs.org>
Co-authored-by: Yannick Welsch <yannick@welsch.lu>
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