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https://issues.apache.org/jira/browse/FLINK-14701?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16981117#comment-16981117
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Zhu Zhu commented on FLINK-14701:
---------------------------------
This issue is not critical now since {{SharedSlotOversubscribedException}} is
removed in FLINK-14314.
However, the proposed change is still valid to avoid similar issue to happen in
the future.
The proposed change is small, at no cost nor risk. So I'd still like to have
the proposed change for {{MultiTaskSlot#releaseChild}}.
> Slot leaks if SharedSlotOversubscribedException happens
> -------------------------------------------------------
>
> Key: FLINK-14701
> URL: https://issues.apache.org/jira/browse/FLINK-14701
> Project: Flink
> Issue Type: Bug
> Components: Runtime / Coordination
> Affects Versions: 1.10.0, 1.9.2
> Reporter: Zhu Zhu
> Priority: Major
> Fix For: 1.10.0, 1.9.2
>
>
> If a {{SharedSlotOversubscribedException}} happens, the {{MultiTaskSlot}}
> will release some of its child {{SingleTaskSlot}}. The triggered releasing
> will trigger a re-allocation of the task slot right inside
> {{SingleTaskSlot#release(...)}}. So that a previous allocation in
> {{SloSharingManager#allTaskSlots}} will be replaced by the new allocation
> because they share the same {{slotRequestId}}.
> However, the {{SingleTaskSlot#release(...)}} will then invoke
> {{MultiTaskSlot#releaseChild}} to release the previous allocation with the
> {{slotRequestId}}, which will unexpectedly remove the new allocation from the
> {{SloSharingManager}}.
> In this way, slot leak happens because the pending slot request is not
> tracked by the {{SloSharingManager}} and cannot be released when its payload
> terminates.
> A test case {{testNoSlotLeakOnSharedSlotOversubscribedException}} which
> exhibits this issue can be found in this
> [commit|https://github.com/zhuzhurk/flink/commit/9024e2e9eb4bd17f371896d6dbc745bc9e585e14].
> The slot leak blocks the TPC-DS queries on flink 1.10, see FLINK-14674.
> To solve it, I'd propose to strengthen the {{MultiTaskSlot#releaseChild}} to
> only remove its true child task slot from the {{SloSharingManager}}, i.e. add
> a check {{if (child == allTaskSlots.get(child.getSlotRequestId()))}} before
> invoking {{allTaskSlots.remove(child.getSlotRequestId())}}.
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