Uploaded image for project: 'Hadoop Common'
  1. Hadoop Common
  2. HADOOP-6502

DistributedFileSystem#listStatus is very slow when listing a directory with a size of 1300

    XMLWordPrintableJSON

Details

    • Bug
    • Status: Resolved
    • Critical
    • Resolution: Fixed
    • 0.20.0
    • 0.23.2
    • util
    • None
    • Reviewed

    Description

      When listing a directory of around 1300 children, it takes hundreds of milliseconds. It turns out the slowdowness is caused by the change made by HADOOP-4187. The return value of listStatus is an array of FileStatus. When deserializing each element of the array, ReflectionUtils#newInstance(Class<T>, Configuration) is called and then calls setConf, which calls setJobConf. SetJobConf checks if JobConf is on the class path by calling Configuration#getClassByName. Even though Configuration#getClassByName tries to optimize the lookup using a cached map, but since JobConf is not in the class path, so it is not in the cache. Every checkup ends up calling Class.ForName which is very expensive. Deserializing an array of 1300 entries requires calling of Class#ForName 1300 times!

      Attachments

        1. hadoop-6502-trunk.txt
          1 kB
          Todd Lipcon
        2. hadoop-6502-trunk.txt
          4 kB
          Todd Lipcon
        3. 6502.patch
          1 kB
          Sharad Agarwal
        4. 6502_v2.patch
          1 kB
          Sharad Agarwal

        Issue Links

          Activity

            People

              sharadag Sharad Agarwal
              hairong Hairong Kuang
              Votes:
              0 Vote for this issue
              Watchers:
              16 Start watching this issue

              Dates

                Created:
                Updated:
                Resolved: