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https://issues.apache.org/jira/browse/FLINK-20748?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17255955#comment-17255955
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Chesnay Schepler commented on FLINK-20748:
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The name doesn't seem appropriate; a change in requirements does not not imply
a change for a slot.
I also don't think you can just call a common method for both cases without
throwing away some optimization potential;
- if a slot is freed you only need to check whether this very slot can fulfill
any other requirement; all other slots are irrelevant
- if a requirement is increased you only need to check whether this very
requirement can be fulfilled by any excess slot; all other requirements are
irrelevant
- if a requirement is reduced you need to check whether this results in excess
free slots, and if so go through the process for freed slots.
A simpler approach might be to try this remapping when a slot is about to be
released due to being idle; you may want to look into that.
> 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
> Priority: Major
> 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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