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From "Apache Spark (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (SPARK-23973) Remove consecutive sorts
Date Sat, 14 Apr 2018 11:13:00 GMT

    [ https://issues.apache.org/jira/browse/SPARK-23973?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16438314#comment-16438314
] 

Apache Spark commented on SPARK-23973:
--------------------------------------

User 'mgaido91' has created a pull request for this issue:
https://github.com/apache/spark/pull/21072

> Remove consecutive sorts
> ------------------------
>
>                 Key: SPARK-23973
>                 URL: https://issues.apache.org/jira/browse/SPARK-23973
>             Project: Spark
>          Issue Type: Improvement
>          Components: SQL
>    Affects Versions: 2.4.0
>            Reporter: Henry Robinson
>            Priority: Minor
>
> As a follow-on from SPARK-23375, it would be easy to remove redundant sorts in the following
kind of query:
> {code}
> Seq((1), (3)).toDF("int").orderBy('int.asc).orderBy('int.desc).explain()
> == Physical Plan ==
> *(2) Sort [int#35 DESC NULLS LAST], true, 0
> +- Exchange rangepartitioning(int#35 DESC NULLS LAST, 200)
>    +- *(1) Sort [int#35 ASC NULLS FIRST], true, 0
>       +- Exchange rangepartitioning(int#35 ASC NULLS FIRST, 200)
>          +- LocalTableScan [int#35]
> {code}
> There's no need to perform {{(1) Sort}}. Since the sort operator isn't stable, AFAIK,
it should be ok to remove a sort on any column that gets 'overwritten' by a subsequent one
in this way. 



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