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https://issues.apache.org/jira/browse/SPARK-2554?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14065621#comment-14065621
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Michael Armbrust commented on SPARK-2554:
-----------------------------------------
I think this may be hard to do if there are other aggregates in the same query,
though I could be wrong.
If there are only distinct aggregates in the query you could just add a logical
rewrite rule:
{code}
Aggregate CountDistinct(x)
Relation
{code}
to
{code}
Aggregate Count(x)
Distinct
Project (x)
Relation
{code}
> CountDistinct and SumDistinct should do partial aggregation
> -----------------------------------------------------------
>
> Key: SPARK-2554
> URL: https://issues.apache.org/jira/browse/SPARK-2554
> Project: Spark
> Issue Type: Improvement
> Components: SQL
> Affects Versions: 1.0.1, 1.0.2
> Reporter: Cheng Lian
>
> {{CountDistinct}} and {{SumDistinct}} should first do a partial aggregation
> and return unique value sets in each partition as partial results. Shuffle IO
> can be greatly reduced in in cases that there are only a few unique values.
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