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https://issues.apache.org/jira/browse/FLINK-7870?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16237447#comment-16237447
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ASF GitHub Bot commented on FLINK-7870:
---------------------------------------

Github user tillrohrmann commented on a diff in the pull request:

    https://github.com/apache/flink/pull/4887#discussion_r148754465
  
    --- Diff: 
flink-runtime/src/main/java/org/apache/flink/runtime/resourcemanager/slotmanager/SlotManager.java
 ---
    @@ -302,7 +302,12 @@ public boolean unregisterSlotRequest(AllocationID 
allocationId) {
                PendingSlotRequest pendingSlotRequest = 
pendingSlotRequests.remove(allocationId);
     
                if (null != pendingSlotRequest) {
    -                   cancelPendingSlotRequest(pendingSlotRequest);
    +                   if (pendingSlotRequest.isAssigned()) {
    +                           cancelPendingSlotRequest(pendingSlotRequest);
    +                   }
    +                   else {
    +                           
resourceActions.cancelResourceAllocation(pendingSlotRequest.getResourceProfile());
    --- End diff --
    
    Then this should be added as a separate feature because it is not strictly 
required by this PR here.
    
    Furthermore, I'm not sure whether this shouldn't be the responsibility of 
the `ResourceManager`. E.g. we could think about adding a timeout for container 
requests after which we cancel them. Additionally, if we add support for 
starting machines with multiple slots, then we shouldn't release a requested 
resource if only a single of it slots is no longer needed. That is something 
else to consider before adding the cancel resource allocation method.


> SlotPool should cancel the slot request to RM if not need any more.
> -------------------------------------------------------------------
>
>                 Key: FLINK-7870
>                 URL: https://issues.apache.org/jira/browse/FLINK-7870
>             Project: Flink
>          Issue Type: Bug
>          Components: Cluster Management
>            Reporter: shuai.xu
>            Assignee: shuai.xu
>            Priority: Major
>              Labels: flip-6
>
> 1. SlotPool will request slot to rm if its slots are not enough.
> 2. If a slot request is not fulfilled in a certain time, SlotPool will treat 
> the request as timeout and send a new slot request by triggering a failover 
> in JobMaster, the previous request is not needed any more, but rm does not 
> know it.
> 3. This may cause the rm request much more resource than the job really need.
> For example:
> 1. A job need 100 slots. RM request 100 container to YARN.
> 2. But YARN is busy now, it has no resource for the job.
> 3. The job failover as the resource request not fulfilled in time.
> 4. It ask 100 slots again, now RM request 200 container to YARN.
> 5. If failover server time, the containers request  will become more and more.
> 6. Now YARN has resource, it will find that the job may need thousands of 
> containers. This is a waste of resources.



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