Teddy Choi created HIVE-20873:

             Summary: Use Murmur hash for VectorHashKeyWrapperTwoLong to reduce 
hash collision
                 Key: HIVE-20873
                 URL: https://issues.apache.org/jira/browse/HIVE-20873
             Project: Hive
          Issue Type: Improvement
            Reporter: Teddy Choi
            Assignee: Teddy Choi

VectorHashKeyWrapperTwoLong is implemented with few bit shift operators and XOR 
operators for short computation time, but more hash collision. Group by 
operations become very slow on large data sets. It needs Murmur hash or a 
better hash function for less hash collision.

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