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From "Shengyang Sha (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (YARN-9195) RM Queue's pending container number might get decreased unexpectedly or even become negative once RM failover
Date Mon, 11 Feb 2019 11:19:00 GMT

    [ https://issues.apache.org/jira/browse/YARN-9195?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16764868#comment-16764868
] 

Shengyang Sha commented on YARN-9195:
-------------------------------------

hi,[~leftnoteasy] The patch is ready for reviewing. Have you had time to look into this
?

> RM Queue's pending container number might get decreased unexpectedly or even become negative
once RM failover
> -------------------------------------------------------------------------------------------------------------
>
>                 Key: YARN-9195
>                 URL: https://issues.apache.org/jira/browse/YARN-9195
>             Project: Hadoop YARN
>          Issue Type: Bug
>          Components: client
>    Affects Versions: 3.1.0
>            Reporter: Shengyang Sha
>            Assignee: Shengyang Sha
>            Priority: Critical
>         Attachments: YARN-9195.001.patch, YARN-9195.002.patch, cases_to_recreate_negative_pending_requests_scenario.diff
>
>
> Hi, all:
> Previously we have encountered a serious problem in ResourceManager, we found that pending
container number of one RM queue became negative after RM failed over. Since queues in RM
are managed in hierarchical structure, the root queue's pending containers became negative
at last, thus the scheduling process of the whole cluster became affected.
> The version of both our RM server and AMRM client in our application are based on yarn
3.1, and we uses AMRMClientAsync#addSchedulingRequests() method in our application to request
resources from RM.
> After investigation, we found that the direct cause was numAllocations of some AMs' requests
became negative after RM failed over. And there are at lease three necessary conditions:
> (1) Use schedulingRequests in AMRM client, and the application set zero to the numAllocations
for a schedulingRequest. In our batch job scenario, the numAllocations of a schedulingRequest
could turn to zero because theoretically we can run a full batch job using only one container.
> (2) RM failovers.
> (3) Before AM reregisters itself to RM after RM restarts, RM has already recovered some
of the application's containers assigned before.
> Here are some more details about the implementation:
> (1) After RM recovers, RM will send all alive containers to AM once it re-register itself
through RegisterApplicationMasterResponse#getContainersFromPreviousAttempts.
> (2) During registerApplicationMaster, AMRMClientImpl will removeFromOutstandingSchedulingRequests
once AM gets ContainersFromPreviousAttempts without checking whether these containers have
been assigned before. As a consequence, its outstanding requests might be decreased unexpectedly
even if it may not become negative.
> (3) There is no sanity check in RM to validate requests from AMs.
> For better illustrating this case, I've written a test case based on the latest hadoop
trunk, posted in the attachment. You may try case testAMRMClientWithNegativePendingRequestsOnRMRestart
and testAMRMClientOnUnexpectedlyDecreasedPendingRequestsOnRMRestart .
> To solve this issue, I propose to filter allocated containers before removeFromOutstandingSchedulingRequests
in AMRMClientImpl during registerApplicationMaster, and some sanity checks are also needed
to prevent things from getting worse.
> More comments and suggestions are welcomed.



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