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  1. Hadoop HDFS
  2. HDFS-1526

Dfs client name for a map/reduce task should have some randomness

    Details

    • Type: Bug
    • Status: Resolved
    • Priority: Major
    • Resolution: Fixed
    • Affects Version/s: None
    • Fix Version/s: 0.23.0
    • Component/s: hdfs-client
    • Labels:
      None
    • Hadoop Flags:
      Incompatible change, Reviewed
    • Release Note:
      Make a client name has this format: DFSClient_applicationid_randomint_threadid, where applicationid = mapred.task.id or else = "NONMAPREDUCE".

      Description

      Fsck shows one of the files in our dfs cluster is corrupt.

      /bin/hadoop fsck aFile -files -blocks -locations
      aFile: 4633 bytes, 2 block(s):
      aFile: CORRUPT block blk_-4597378336099313975
      OK
      0. blk_-4597378336099313975_2284630101 len=0 repl=3 [...]
      1. blk_5024052590403223424_2284630107 len=4633 repl=3 [...]Status: CORRUPT

      On disk, these two blocks are of the same size and the same content. It turns out the writer of the file is from a multiple threaded map task. Each thread may write to the same file. One possible interaction of two threads might make this to happen:
      [T1: create aFile] [T2: delete aFile] [T2: create aFile][T1: addBlock 0 to aFile][T2: addBlock1 to aFile]...

      Because T1 and T2 have the same client name, which is the map task id, the above interactions could be done without any lease exception, thus eventually leading to a corrupt file. To solve the problem, a mapreduce task's client name could be formed by its task id followed by a random number.

        Attachments

        1. clientName.patch
          0.5 kB
          Hairong Kuang
        2. randClientId1.patch
          13 kB
          Hairong Kuang
        3. randClientId2.patch
          0.9 kB
          Hairong Kuang
        4. randClientId3.patch
          1 kB
          Hairong Kuang

          Activity

            People

            • Assignee:
              hairong Hairong Kuang
              Reporter:
              hairong Hairong Kuang
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              Dates

              • Created:
                Updated:
                Resolved: