Jesus Camacho Rodriguez created HIVE-17043:
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Summary: Remove non unique columns from group by keys if not
referenced later
Key: HIVE-17043
URL: https://issues.apache.org/jira/browse/HIVE-17043
Project: Hive
Issue Type: Sub-task
Components: Logical Optimizer
Affects Versions: 3.0.0
Reporter: Ashutosh Chauhan
Group by keys may be a mix of unique (or primary) keys and regular columns. In
such cases presence of regular column won't alter cardinality of groups. So, if
regular columns are not referenced later, they can be dropped from group by
keys. Depending on operator tree may result in those columns not being read at
all from disk in best case. In worst case, we will avoid shuffling and sorting
regular columns from mapper to reducer, which still could be substantial CPU
and network savings.
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