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  1. Hadoop HDFS
  2. HDFS-4879

Add "blocked ArrayList" collection to avoid CMS full GCs

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    Details

    • Type: Improvement
    • Status: Closed
    • Priority: Major
    • Resolution: Fixed
    • Affects Version/s: 2.0.4-alpha, 3.0.0-alpha1
    • Fix Version/s: 2.3.0
    • Component/s: namenode
    • Labels:
      None
    • Target Version/s:

      Description

      We recently saw an issue where a large deletion was issued which caused 25M blocks to be collected during deleteInternal. Currently, the list of collected blocks is an ArrayList, meaning that we had to allocate a contiguous 25M-entry array (~400MB). After a NN has been running for a long amount of time, the old generation may become fragmented such that it's hard to find a 400MB contiguous chunk of heap.

      In general, we should try to design the NN such that the only large objects are long-lived and created at startup time. We can improve this particular case (and perhaps some others) by introducing a new List implementation which is made of a linked list of arrays, each of which is size-limited (eg to 1MB).

        Attachments

        1. hdfs-4879.txt
          16 kB
          Todd Lipcon
        2. hdfs-4879.txt
          16 kB
          Todd Lipcon
        3. hdfs-4879.txt
          49 kB
          Todd Lipcon
        4. hdfs-4879.txt
          48 kB
          Todd Lipcon

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            • Assignee:
              tlipcon Todd Lipcon
              Reporter:
              tlipcon Todd Lipcon
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              Dates

              • Created:
                Updated:
                Resolved: