[jira] [Created] (FLINK-20748) Remap excess slots to outstanding requirements

[Shang Yuanchun (Jira)]

Chesnay Schepler created FLINK-20748:
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             Summary: Remap excess slots to outstanding requirements
                 Key: FLINK-20748
                 URL: https://issues.apache.org/jira/browse/FLINK-20748
             Project: Flink
          Issue Type: Improvement
          Components: Runtime / Coordination
    Affects Versions: 1.13.0
            Reporter: Chesnay Schepler
             Fix For: 1.13.0


The {{DeclarativeSlotPool}} maintains a mapping of slots to requirements that they fulfill.   This mapping is currently determined when the slot is offered to the pool, and is only modified if the scheduler reserves this slot for a different requirement.

This currently implies 2 things:
 * a slot can be prematurely released, although it could fulfill a different outstanding requirement
 * a new slot could be requested, despite there being another slot around that could fulfill the requirement

We should remedy this by checking whether excess slots can be re-mapped to a different requirement, whenever the requirements change or a slot is freed.



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