[jira] [Created] (YARN-4095) Avoid sharing AllocatorPerContext object in LocalDirAllocator between ShuffleHandler and LocalDirsHandlerService.

["zhihai xu (JIRA)" <ji...@apache.org>]

zhihai xu created YARN-4095:
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             Summary: 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


Currently {{ShuffleHandler}} and {{LocalDirsHandlerService}} share {{AllocatorPerContext}} object in {{LocalDirAllocator}} for configuration {{NM_LOCAL_DIRS}} because {{AllocatorPerContext}}s 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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