Zhu Zhu created FLINK-14607:
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Summary: SharedSlot cannot fulfill pending slot requests before it's totally 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
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 slot is qualified for 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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