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https://issues.apache.org/jira/browse/SPARK-17289?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15446615#comment-15446615
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Apache Spark commented on SPARK-17289:
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User 'maropu' has created a pull request for this issue:
https://github.com/apache/spark/pull/14865
> Sort based partial aggregation breaks due to SPARK-12978
> --------------------------------------------------------
>
> Key: SPARK-17289
> URL: https://issues.apache.org/jira/browse/SPARK-17289
> Project: Spark
> Issue Type: Bug
> Reporter: Sean Zhong
> Priority: Blocker
>
> For the following query:
> {code}
> val df2 = (0 to 1000).map(x => (x % 2, x.toString)).toDF("a",
> "b").createOrReplaceTempView("t2")
> spark.sql("select max(b) from t2 group by a").explain(true)
> {code}
> Now, the SortAggregator won't insert Sort operator before partial
> aggregation, this will break sort-based partial aggregation.
> {code}
> == Physical Plan ==
> SortAggregate(key=[a#5], functions=[max(b#6)], output=[max(b)#17])
> +- *Sort [a#5 ASC], false, 0
> +- Exchange hashpartitioning(a#5, 200)
> +- SortAggregate(key=[a#5], functions=[partial_max(b#6)], output=[a#5,
> max#19])
> +- LocalTableScan [a#5, b#6]
> {code}
> In Spark 2.0 branch, the plan is:
> {code}
> == Physical Plan ==
> SortAggregate(key=[a#5], functions=[max(b#6)], output=[max(b)#17])
> +- *Sort [a#5 ASC], false, 0
> +- Exchange hashpartitioning(a#5, 200)
> +- SortAggregate(key=[a#5], functions=[partial_max(b#6)], output=[a#5,
> max#19])
> +- *Sort [a#5 ASC], false, 0
> +- LocalTableScan [a#5, b#6]
> {code}
> This is related to SPARK-12978
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