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https://issues.apache.org/jira/browse/YARN-547?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13632691#comment-13632691
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Omkar Vinit Joshi commented on YARN-547:
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There was a problem at my end while creating a patch. resubmitting the patch.
(I took diff against local trunk in which 2 files were already committed.)
> Race condition in Public / Private Localizer may result into resource getting
> downloaded again
> ----------------------------------------------------------------------------------------------
>
> Key: YARN-547
> URL: https://issues.apache.org/jira/browse/YARN-547
> Project: Hadoop YARN
> Issue Type: Sub-task
> Reporter: Omkar Vinit Joshi
> Assignee: Omkar Vinit Joshi
> Attachments: yarn-547-20130411.1.patch, yarn-547-20130411.patch,
> yarn-547-20130412.patch, yarn-547-20130415.patch, yarn-547-20130416.patch
>
>
> Public Localizer :
> At present when multiple containers try to request a localized resource
> * If the resource is not present then first it is created and Resource
> Localization starts ( LocalizedResource is in DOWNLOADING state)
> * Now if in this state multiple ResourceRequestEvents arrive then
> ResourceLocalizationEvents are sent for all of them.
> Most of the times it is not resulting into a duplicate resource download but
> there is a race condition present there. Inside ResourceLocalization (for
> public download) all the requests are added to local attempts map. If a new
> request comes in then first it is checked in this map before a new download
> starts for the same. For the current download the request will be there in
> the map. Now if a same resource request comes in then it will rejected (i.e.
> resource is getting downloaded already). However if the current download
> completes then the request will be removed from this local map. Now after
> this removal if the LocalizerRequestEvent comes in then as it is not present
> in local map the resource will be downloaded again.
> PrivateLocalizer :
> Here a different but similar race condition is present.
> * Here inside findNextResource method call; each LocalizerRunner tries to
> grab a lock on LocalizerResource. If the lock is not acquired then it will
> keep trying until the resource state changes to LOCALIZED. This lock will be
> released by the LocalizerRunner when download completes.
> * Now if another ContainerLocalizer tries to grab the lock on a resource
> before LocalizedResource state changes to LOCALIZED then resource will be
> downloaded again.
> At both the places the root cause of this is that all the threads try to
> acquire the lock on resource however current state of the LocalizedResource
> is not taken into consideration.
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