kfaraz commented on PR #18028:
URL: https://github.com/apache/druid/pull/18028#issuecomment-2906351126

   > I have not review the changes carefully, but leave one question first, 
some kill tasks might take very long time(for example, up to dozens of minutes) 
to delete segments for large data source, if there're several such kill tasks 
run together, wil these kill tasks block the overlord's other duties?
   
   Thanks for the comment, @FrankChen021 !
   
   A couple of clarifications on the above:
   - When embedded kill tasks are running on the Overlord, it is recommended to 
NOT launch kill tasks
   manually or from the coordinator duty.
   It is currently not possible to validate this in the code itself since the 
new config
   `druid.manager.segments.killUnused.enable` is required on the Overlord 
whereas
   the old one `druid.coordinator.kill.enabled` is required on the Coordinator.
   - Embedded kill tasks run on a single thread on the Overlord. So, there can 
be only one.
   - Since it is a dedicated thread, it does not interfere with other Overlord 
activities.
   - It cannot take a long time even for large datasources since each embedded 
kill task will
   only ever kill at most 1000 segments in a single interval. So the total time 
would be just the
   time taken to delete 1000 segments from metadata store and deep storage.
   - WIP: If a single kill task still somehow gets stuck, there is a management 
ping sent from `OverlordDutyExecutor`
   that will kill off that task.
   
   Thanks for bringing this up, I will also add the above points to the PR 
description (and perhaps some points 
   to the code javadoc as well) to help future readers.


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