[HIVE-757] Don't send constants from mapper to reducer for Group By queries

• Type: Improvement
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Assignee: Zheng Shao
• Reporter: Zheng Shao
• Created: 15/Aug/09 01:23
• Updated: 28/Sep/12 00:47

Description

If an aggregation function takes a constant expression, we are still sending it from mapper to reducer, but it's not necessary since we can compute the constants on the reducer side.

This will be useful for some UDAF that have configuration parameters:

SELECT pageid, logistic_regression("-t 1.0 -b 2.0", col1, col2, col3) FROM mytable GROUP BY pageid;

Issue Links

• is duplicated by: HIVE-3511 Constant values in aggregation parameters should not be attached to every map output row
• is part of: HIVE-746 constant folding