Github user pwendell commented on a diff in the pull request:

    https://github.com/apache/spark/pull/2087#discussion_r18795734
  
    --- Diff: core/src/main/scala/org/apache/spark/deploy/SparkHadoopUtil.scala 
---
    @@ -121,6 +125,31 @@ class SparkHadoopUtil extends Logging {
         UserGroupInformation.loginUserFromKeytab(principalName, keytabFilename)
       }
     
    +  /**
    +   * Returns a function that can be called to find the number of Hadoop 
FileSystem bytes read by
    +   * this thread so far. Reflection is required because thread-level 
FileSystem statistics are only
    +   * available as of Hadoop 2.5 (see HADOOP-10688). Returns None if the 
required method can't be
    +   * found.
    +   */
    +  def getInputBytesReadCallback(path: Path, conf: Configuration): 
Option[() => Long] = {
    --- End diff --
    
    Hey so there are a couple issues with the current approach:
    
    This a bunch of reflective calls + exception handling every time it is 
called. That will have huge performance overhead. Also, this catch-all 
exception is sort of scary... what if there is a legitimate exception invoking 
this function in versions that support it? The user will never be able to find 
it.


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