Improve distribution of keys in reduce phase

                 Key: PIG-871
             Project: Pig
          Issue Type: Improvement
    Affects Versions: 0.3.0
            Reporter: Ankur

The default hashing scheme used to distribute keys in reduce phase sometimes 
results in an uneven distribution of keys resulting in 5 - 10 % of reducers 
being overloaded with data. This bottleneck makes the PIG jobs really slow and 
gives users a bad impression.

While there is no bullet proof solution to the problem in general, the hashing 
can certainly be improved for better distribution. The proposal here is to 
evaluate and incorporate other hashing schemes that give high avalanche and 
more even distribution. We can start by evaluating MurmurHash which is Apache 
2.0 licensed and freely available here -

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