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From "Jingkei Ly (JIRA)" <j...@apache.org>
Subject [jira] Created: (HADOOP-5589) TupleWritable: Lift implicit limit on the number of values that can be stored
Date Fri, 27 Mar 2009 12:16:50 GMT
TupleWritable: Lift implicit limit on the number of values that can be stored
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                 Key: HADOOP-5589
                 URL: https://issues.apache.org/jira/browse/HADOOP-5589
             Project: Hadoop Core
          Issue Type: Improvement
          Components: mapred
    Affects Versions: 0.21.0
            Reporter: Jingkei Ly


TupleWritable uses an instance field of the primitive type, long, which I presume is so that
it can quickly determine if a position has been written to in its array of Writables (by using
bit-shifting operations on the long field). The problem with this is that it implies that
there is a maximum limit of 64 values you can store in a TupleWritable.

An example of a use-case where I think this would be a problem is if you had two MR jobs with
over 64 reduces tasks and you wanted to join the outputs with CompositeInputFormat  - this
will probably cause unexpected results in the current scheme.

At the very least, the 64-value limit should be documented in TupleWritable.



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