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https://issues.apache.org/jira/browse/FLINK-7851?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Till Rohrmann reassigned FLINK-7851:
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Assignee: Till Rohrmann
> Improve scheduling balance in case of fewer sub tasks than input operator
> -------------------------------------------------------------------------
>
> Key: FLINK-7851
> URL: https://issues.apache.org/jira/browse/FLINK-7851
> Project: Flink
> Issue Type: Improvement
> Components: Distributed Coordination
> Affects Versions: 1.4.0, 1.3.2
> Reporter: Till Rohrmann
> Assignee: Till Rohrmann
> Fix For: 1.4.0
>
>
> When having a job where we have a mapper {{m1}} running with dop {{n}}
> followed by a key by and a mapper {{m2}} (all-to-all communication) which
> runs with dop {{m}} and {{n > m}}, it happens that the sub tasks of {{m2}}
> are not uniformly spread out across all currently used {{TaskManagers}}.
> For example: {{n = 4}}, {{m = 2}} and we have 2 TaskManagers with 2 slots
> each. The deployment would look the following:
> TM1:
> Slot 1: {{m1_1}} -> {{m_2_1}}
> Slot 2: {{m1_3}} -> {{m_2_2}}
> TM2:
> Slot 1: {{m1_2}}
> Slot 2: {{m1_4}}
> The problem for this behaviour is that when there are too many preferred
> locations (currently 8) due to an all-to-all communication pattern, then we
> will simply poll the next slot from the MultiMap in
> {{SlotSharingGroupAssignment}}. The polling algorithm first drains all
> available slots for a single machine before it polls slots from another
> machine.
> I think it would be better to poll slots in a round robin fashion wrt to the
> machines. That way we would get a better resource utilisation by spreading
> the tasks more evenly.
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