[jira] [Created] (HIVE-24479) Introduce setting to set lower bound of hash aggregation reduction.

[Krisztian Kasa (Jira)]

Krisztian Kasa created HIVE-24479:
-------------------------------------

             Summary: Introduce setting to set lower bound of hash aggregation 
reduction.
                 Key: HIVE-24479
                 URL: https://issues.apache.org/jira/browse/HIVE-24479
             Project: Hive
          Issue Type: Improvement
          Components: Physical Optimizer
    Affects Versions: 4.0.0
            Reporter: Krisztian Kasa
            Assignee: Krisztian Kasa
             Fix For: 4.0.0


* Default setting of hash group by min reduction % is 0.99. 
* During compilation, we check its effectiveness and adjust it accordingly in 
{{SetHashGroupByMinReduction}}:
{code}
float defaultMinReductionHashAggrFactor = desc.getMinReductionHashAggr();
float minReductionHashAggrFactor = 1f - ((float) ndvProduct / numRows);
if (minReductionHashAggrFactor < defaultMinReductionHashAggrFactor) {
      desc.setMinReductionHashAggr(minReductionHashAggrFactor);
}
{code}
For certain queries, this computation turns out to be "0".

This forces operator to skip HashAggregates completely and always ends up 
choosing streaming mode.



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