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Posted to issues@spark.apache.org by "karl wang (Jira)" <ji...@apache.org> on 2020/08/31 14:58:00 UTC

[jira] [Reopened] (SPARK-32542) Add an optimizer rule to split an Expand into multiple Expands for aggregates

     [ https://issues.apache.org/jira/browse/SPARK-32542?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

karl wang reopened SPARK-32542:
-------------------------------

> Add an optimizer rule to split an Expand into multiple Expands for aggregates
> -----------------------------------------------------------------------------
>
>                 Key: SPARK-32542
>                 URL: https://issues.apache.org/jira/browse/SPARK-32542
>             Project: Spark
>          Issue Type: Improvement
>          Components: SQL
>    Affects Versions: 3.0.0
>            Reporter: karl wang
>            Priority: Major
>
> Split an expand into several small Expand, which contains the Specified number of projections.
> For instance, like this sql.select a, b, c, d, count(1) from table1 group by a, b, c, d with cube. It can expand 2^4 times of original data size.
> Now we specify the spark.sql.optimizer.projections.size=4.The Expand will be split into 2^4/4 smallExpand.It can reduce the shuffle pressure and improve performance in multidimensional analysis when data is huge.



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