Dave Beech created MRUNIT-129:
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Summary: Key object re-use in Reducer is inconsistent with
MapReduce behaviour (new API)
Key: MRUNIT-129
URL: https://issues.apache.org/jira/browse/MRUNIT-129
Project: MRUnit
Issue Type: Bug
Affects Versions: 0.9.0
Reporter: Dave Beech
Follow on issue from MRUNIT-127, also relating to grouping comparators.
In the new MapReduce API Reducer's reduce method, you are passed a reference to
a key and an Iterable for the values. What's not particularly clear is that as
you iterate through the values, the value of the key is also changing silently.
This is not usually noticeable, since the keys that were grouped often have the
same value anyway, but with a custom grouping comparator this isn't necessarily
the case.
This is different to the old API, where you would get the first key in the
group and this wouldn't change as you iterate over the values.
MRUnit uses the "old API" style behaviour for both old and new APIs, so some
unit tests may not give a consistent result to an actual mapreduce job.
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