Na Yang created HIVE-8638:
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             Summary: Implement bucket map join optimization [Spark Branch]
                 Key: HIVE-8638
                 URL: https://issues.apache.org/jira/browse/HIVE-8638
             Project: Hive
          Issue Type: Task
          Components: Spark
            Reporter: Na Yang
            Assignee: Na Yang


In the hive-on-mr implementation, bucket map join optimization has to depend on 
the map join hint. While in the hive-on-tez implementation, a join can be 
automatically converted to bucket map join if certain conditions are met such 
as: 
1. the optimization flag hive.convert.join.bucket.mapjoin.tez is ON
2. all join tables are buckets and each small table's bucket number can be 
divided by big table's bucket number
3. bucket columns == join columns

In the hive-on-spark implementation, it is ideal to have the bucket map join 
auto-convertion support. when all the required criteria are met, a join can be 
automatically converted to a bucket map join.






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