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MapReduce Forum

Why hadoop uses default Longwritable or Intwritable

  • #55417
    Hutashan Chandrakar

    Why hadoop uses default Longwritable or Intwritable ? Why Hadoop framework didnt use some other class to write.

  • Author
  • #55420
    Steve Loughran

    they’ve got two features that are relevant

    1. they have the “Writable” interface -they know how to write to a DataOutput stream and read from a DataInput stream -explicitly.
    2. they have their contents updates via the set() operation. This lets you reuse the same value, repeatedly, without creating new instances. It’s a lot more efficient if the same mapper or reducer is called repeatedly: you just create your instances of the writables in the constructor and reuse them

      In comparison, Java’s Serializable framework “magically” serializes objects -but it does it in a way that is a bit brittle and is generally impossible to read in values generated by older versions of a class. the Java Object stream is designed to send a graph of objects back -it has to remember every object reference pushed out already, and do the same on the way back. The writables are designed to be self contained.

The forum ‘MapReduce’ is closed to new topics and replies.

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