[jira] [Updated] (SPARK-30523) Collapse back to back aggregations into a single aggregate to reduce the number of shuffles

["Dongjoon Hyun (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/SPARK-30523?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Dongjoon Hyun updated SPARK-30523:
----------------------------------
    Component/s:     (was: Optimizer)
                 SQL

> 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: 3.0.0
>            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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