Github user tison1 commented on the issue:
https://github.com/apache/flink/pull/6360
> When task executor report a slotA with allocationId1, it may happen that
slot manager record slotA is assigned to allocationId2, and the slot request
with allocationId1 is not assigned. Then slot manager will update itself with
slotA assigned to allocationId1, by it does not clear the slot request with
allocationId1.
>
> For example:
> \# There is one free slot in slot manager.
> \# Now come two slot request with allocationId1 and allocationId2.
> \# The slot is assigned to allocationId1, but the requestSlot call
timeout.
> \# SlotManager assign the slot to allocationId2 and insert a slot
request with allocationId1.
> \# The second requestSlot call to task executor return
SlotOccupiedException.
> \# SlotManager update the slot to allocationID1, but the slot request is
left.
pick from the assigned JIRA for further discuss
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