[jira] [Created] (FLINK-14701) Slot leaks if SharedSlotOversubscribedException happens

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

Zhu Zhu created FLINK-14701:
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             Summary: 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
             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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