Details
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Improvement
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Status: Closed
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Major
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Resolution: Fixed
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0.19.1
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None
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None
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Reviewed
Description
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.