zhihai xu updated YARN-4095:
    Attachment: YARN-4095.001.patch

> Avoid sharing AllocatorPerContext object in LocalDirAllocator between 
> ShuffleHandler and LocalDirsHandlerService.
> -----------------------------------------------------------------------------------------------------------------
>                 Key: YARN-4095
>                 URL: https://issues.apache.org/jira/browse/YARN-4095
>             Project: Hadoop YARN
>          Issue Type: Improvement
>          Components: nodemanager
>            Reporter: zhihai xu
>            Assignee: zhihai xu
>         Attachments: YARN-4095.000.patch, YARN-4095.001.patch
> Currently {{ShuffleHandler}} and {{LocalDirsHandlerService}} share 
> {{AllocatorPerContext}} object in {{LocalDirAllocator}} for configuration 
> {{NM_LOCAL_DIRS}} because {{AllocatorPerContext}} are stored in a static 
> TreeMap with configuration name as key
> {code}
>   private static Map <String, AllocatorPerContext> contexts = 
>                  new TreeMap<String, AllocatorPerContext>();
> {code}
> {{LocalDirsHandlerService}} and {{ShuffleHandler}} both create a 
> {{LocalDirAllocator}} using {{NM_LOCAL_DIRS}}. Even they don't use the same 
> {{Configuration}} object, but they will use the same {{AllocatorPerContext}} 
> object. Also {{LocalDirsHandlerService}} may change {{NM_LOCAL_DIRS}} value 
> in its {{Configuration}} object to exclude full and bad local dirs, 
> {{ShuffleHandler}} always uses the original {{NM_LOCAL_DIRS}} value in its 
> {{Configuration}} object. So every time {{AllocatorPerContext#confChanged}} 
> is called by {{ShuffleHandler}} after {{LocalDirsHandlerService}}, 
> {{AllocatorPerContext}} need be reinitialized because {{NM_LOCAL_DIRS}} value 
> is changed. This will cause some overhead.
> {code}
>       String newLocalDirs = conf.get(contextCfgItemName);
>       if (!newLocalDirs.equals(savedLocalDirs)) {
> {code}
> So it will be a good improvement to not share the same 
> {{AllocatorPerContext}} instance between {{ShuffleHandler}} and 
> {{LocalDirsHandlerService}}.

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