[jira] [Commented] (SPARK-17271) Planner adds un-necessary Sort even if child ordering is semantically same as required ordering

["Apache Spark (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SPARK-17271?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15440557#comment-15440557 ] 

Apache Spark commented on SPARK-17271:
--------------------------------------

User 'tejasapatil' has created a pull request for this issue:
https://github.com/apache/spark/pull/14841

> Planner adds un-necessary Sort even if child ordering is semantically same as required ordering
> -----------------------------------------------------------------------------------------------
>
>                 Key: SPARK-17271
>                 URL: https://issues.apache.org/jira/browse/SPARK-17271
>             Project: Spark
>          Issue Type: Bug
>          Components: SQL
>    Affects Versions: 1.6.2, 2.0.0
>            Reporter: Tejas Patil
>
> Found a case when the planner is adding un-needed SORT operation due to bug in the way comparison for `SortOrder` is done at https://github.com/apache/spark/blob/master/sql/core/src/main/scala/org/apache/spark/sql/execution/exchange/EnsureRequirements.scala#L253
> `SortOrder` needs to be compared semantically because `Expression` within two `SortOrder` can be "semantically equal" but not literally equal objects.
> eg. In case of `sql("SELECT * FROM table1 a JOIN table2 b ON a.col1=b.col1")`
> Expression in required SortOrder:
> {code}
>       AttributeReference(
>         name = "col1",
>         dataType = LongType,
>         nullable = false
>       ) (exprId = exprId,
>         qualifier = Some("a")
>       )
> {code}
> Expression in child SortOrder:
> {code}
>       AttributeReference(
>         name = "col1",
>         dataType = LongType,
>         nullable = false
>       ) (exprId = exprId)
> {code}
> Notice that the output column has a qualifier but the child attribute does not but the inherent expression is the same and hence in this case we can say that the child satisfies the required sort order.



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