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https://issues.apache.org/jira/browse/SPARK-30523?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Dongjoon Hyun updated SPARK-30523:
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Affects Version/s: (was: 3.0.0)
3.1.0
> Collapse back to back aggregations into a single aggregate to reduce the
> number of shuffles
> -------------------------------------------------------------------------------------------
>
> Key: SPARK-30523
> URL: https://issues.apache.org/jira/browse/SPARK-30523
> Project: Spark
> Issue Type: Improvement
> Components: SQL
> Affects Versions: 3.1.0
> Reporter: Jason Altekruse
> Priority: Major
>
> Queries containing nested aggregate operations can in some cases be
> computable with a single phase of aggregation. This Jira seeks to introduce a
> new optimizer rule to identify some of those cases and rewrite plans to avoid
> needlessly re-shuffling and generating the aggregation hash table data twice.
> Some examples of collapsible aggregates:
> {code:java}
> SELECT sum(sumAgg) as a, year from (
> select sum(1) as sumAgg, course, year FROM courseSales GROUP BY course,
> year
> ) group by year
> // can be collapsed to
> SELECT sum(1) as `a`, year from courseSales group by year
> {code}
> {code}
> SELECT sum(agg), min(a), b from (
> select sum(1) as agg, a, b FROM testData2 GROUP BY a, b
> ) group by b
> // can be collapsed to
> SELECT sum(1) as `sum(agg)`, min(a) as `min(a)`, b from testData2 group by b
> {code}
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