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From "W.P. McNeill" <bill...@gmail.com>
Subject Re: Can't print an ArrayWritable as a key even if it implements the ArrayWritable interface
Date Sun, 11 Sep 2011 19:19:01 GMT
With a bit more debugging I may have partially answered question (3) for
myself.

When I run a Hadoop job other than that called by "hadoop fs -text", an
ItemSet key is created by the org.apache.hadoop.ioWritableComparator.newKey
method, which looks like this:

  public WritableComparable newKey() {
    return ReflectionUtils.newInstance(keyClass, null);
  }

Here keyClass is equal to ItemSet.class. Compare this to the call in the
TextRecordInputStream constructor.

      key =
ReflectionUtils.newInstance(r.getKeyClass().asSubclass(WritableComparable.class),
                                        getConf());

This does look related to
HADOOP-4466<https://issues.apache.org/jira/browse/HADOOP-4466>,
but that is listed as fixed in 0.19.0.

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