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https://issues.apache.org/jira/browse/SPARK-4367?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14254020#comment-14254020
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Michael Armbrust commented on SPARK-4367:
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So we already do this for SUM and COUNT, and I don't think there is a AVG
DISTINCT currently. Should we close this or is there more to it?
> Process the "distinct" value before shuffling for aggregation
> -------------------------------------------------------------
>
> Key: SPARK-4367
> URL: https://issues.apache.org/jira/browse/SPARK-4367
> Project: Spark
> Issue Type: Sub-task
> Components: SQL
> Reporter: Cheng Hao
>
> Most of aggregate function(e.g average) with "distinct" value will requires
> all of the records in the same group to be shuffled into a single node,
> however, as part of the optimization, those records can be partially
> aggregated before shuffling, that probably reduces the overhead of shuffling
> significantly.
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