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Posted to issues@spark.apache.org by "Sean Owen (JIRA)" <ji...@apache.org> on 2016/03/06 21:02:40 UTC
[jira] [Resolved] (SPARK-13496) Optimizing count distinct changes
the resulting column name
[ https://issues.apache.org/jira/browse/SPARK-13496?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Sean Owen resolved SPARK-13496.
-------------------------------
Resolution: Duplicate
Provisionally labeling this a duplicate then
> Optimizing count distinct changes the resulting column name
> -----------------------------------------------------------
>
> Key: SPARK-13496
> URL: https://issues.apache.org/jira/browse/SPARK-13496
> Project: Spark
> Issue Type: Bug
> Components: SQL
> Affects Versions: 1.6.0
> Reporter: Ryan Blue
>
> SPARK-9241 updated the optimizer to rewrite count distinct. That change uses a count that is no longer distinct because duplicates are eliminated further down in the plan. This caused the name of the column to change:
> {code:title=Spark 1.5.2}
> scala> Seq((1, "s")).toDF("a", "b").agg(countDistinct("a"))
> res0: org.apache.spark.sql.DataFrame = [COUNT(DISTINCT a): bigint]
> == Physical Plan ==
> TungstenAggregate(key=[], functions=[(count(a#7),mode=Complete,isDistinct=true)], output=[COUNT(DISTINCT a)#9L])
> TungstenAggregate(key=[a#7], functions=[], output=[a#7])
> TungstenExchange SinglePartition
> TungstenAggregate(key=[a#7], functions=[], output=[a#7])
> LocalTableScan [a#7], [[1]]
> {code}
> {code:title=Spark 1.6.0}
> scala> Seq((1, "s")).toDF("a", "b").agg(countDistinct("a"))
> res0: org.apache.spark.sql.DataFrame = [count(a): bigint]
> == Physical Plan ==
> TungstenAggregate(key=[], functions=[(count(if ((gid#35 = 1)) a#36 else null),mode=Final,isDistinct=false)], output=[count(a)#31L])
> +- TungstenExchange SinglePartition, None
> +- TungstenAggregate(key=[], functions=[(count(if ((gid#35 = 1)) a#36 else null),mode=Partial,isDistinct=false)], output=[count#39L])
> +- TungstenAggregate(key=[a#36,gid#35], functions=[], output=[a#36,gid#35])
> +- TungstenExchange hashpartitioning(a#36,gid#35,500), None
> +- TungstenAggregate(key=[a#36,gid#35], functions=[], output=[a#36,gid#35])
> +- Expand [List(a#29, 1)], [a#36,gid#35]
> +- LocalTableScan [a#29], [[1]]
> {code}
> This has broken jobs that used the generated name. For example, {{withColumnRenamed("COUNT(DISTINCT a)", "c")}}.
> I think that the previous generated name is correct, even though the plan has changed.
> [~marmbrus], you may want to take a look. It looks like you reviewed SPARK-9241 and have some context here.
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