[jira] [Closed] (FLINK-14607) SharedSlot cannot fulfill pending slot requests before it's completely released

["Zhu Zhu (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/FLINK-14607?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Zhu Zhu closed FLINK-14607.
---------------------------
    Resolution: Won't Fix

> SharedSlot cannot fulfill pending slot requests before it's completely released
> -------------------------------------------------------------------------------
>
>                 Key: FLINK-14607
>                 URL: https://issues.apache.org/jira/browse/FLINK-14607
>             Project: Flink
>          Issue Type: Bug
>          Components: Runtime / Coordination
>    Affects Versions: 1.9.1, 1.10.0
>            Reporter: Zhu Zhu
>            Priority: Minor
>
> Currently a pending request can only be fulfilled when a physical slot({{AllocatedSlot}}) becomes available in {{SlotPool}}.
> A shared slot however, cannot be used to fulfill pending requests even if it becomes qualified. This may lead to resource deadlocks in certain cases.
> For example, running job A(parallelism=2) --(pipelined)--> B(parallelism=2) with 1 slot only, all vertices are in the same slot sharing group, here's what may happen:
> 1. Schedule A1 and A2. A1 acquires the only slot, A2's slot request is pending because a slot cannot host 2 instances of the same JobVertex at the same time. Shared slot status: \{A1\}
> 2. A1 produces data and triggers the scheduling of B1. Shared slot status: \{A1, B1\}
> 3. A1 finishes. Shared slot status: \{B1\}
> 4. B1 cannot finish since A2 has not finished, while A2 cannot get launched due to no physical slot becomes available, even though the shred slot is qualified to host it now. A resource deadlock happens.
> Maybe we should improve {{SlotSharingManager}}. One a task slot is released, its root {{MultiTaskSlot}} should be used to try fulfilling existing pending task slots from other pending root slots({{unresolvedRootSlots}}) in this {{SlotSharingManager}}(means in the same slot sharing group).
> We need to be careful to not cause any failures, and do not violate colocation constraints.
> cc [~trohrmann]



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