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POSerialization using ArrayWritable seems to work in a funny way
 

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  1. POSerialization using ArrayWritable seems to work in a funny way
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    <p>I was working with <code>ArrayWritable</code>, at some point I needed to check how Hadoop serializes the <code>ArrayWritable</code>, this is what I got by setting <code>job.setNumReduceTasks(0)</code>:</p> <pre><code>0    IntArrayWritable@10f11b8 3    IntArrayWritable@544ec1 6    IntArrayWritable@fe748f 8    IntArrayWritable@1968e23 11    IntArrayWritable@14da8f4 14    IntArrayWritable@18f6235 </code></pre> <p>and this is the test mapper that I was using:</p> <pre><code>public static class MyMapper extends Mapper&lt;LongWritable, Text, LongWritable, IntArrayWritable&gt; { public void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException { int red = Integer.parseInt(value.toString()); IntWritable[] a = new IntWritable[100]; for (int i =0;i&lt;a.length;i++){ a[i] = new IntWritable(red+i); } IntArrayWritable aw = new IntArrayWritable(); aw.set(a); context.write(key, aw); } } </code></pre> <p><code>IntArrayWritable</code> is taken from the example given in the javadoc: <a href="http://hadoop.apache.org/common/docs/current/api/org/apache/hadoop/io/ArrayWritable.html" rel="nofollow">ArrayWritable</a>.</p> <pre><code>import org.apache.hadoop.io.ArrayWritable; import org.apache.hadoop.io.IntWritable; public class IntArrayWritable extends ArrayWritable { public IntArrayWritable() { super(IntWritable.class); } } </code></pre> <p>I actually checked on the source code of Hadoop and this makes no sense to me. <code>ArrayWritable</code> should not serialize the class name and there is no way that an array of 100 <code>IntWritable</code> can be serialized using 6/7 hexadecimal values. The application actually seems to work just fine and the reducer deserializes the right values... What is happening? What am I missing?</p>
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    1. CO`IntArrayWritable@10f11b8` seems like aw.toString() to me. can you please post the code where you get `IntArrayWritable@10f11b8`. I guess the problem is you are not getting the "serialized" data but the object's toString method.
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    2. COI added the IntArrayWritable class. It should inherit from ArrayWritable the serialization methods, specifically public void write(DataOutput out). I agree that the output seems a toString() but I don't know why this is happening.
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