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From "Omkar Vinit Joshi (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (YARN-547) Race condition in Public / Private Localizer may result into resource getting downloaded again
Date Tue, 16 Apr 2013 09:29:16 GMT

     [ https://issues.apache.org/jira/browse/YARN-547?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Omkar Vinit Joshi updated YARN-547:
-----------------------------------

    Attachment: yarn-547-20130416.1.patch
    
> 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-547-20130416.1.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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