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https://issues.apache.org/jira/browse/SPARK-11135?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Josh Rosen updated SPARK-11135:
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Summary: Exchange sort-planning logic incorrectly avoid sorts when existing
ordering is non-empty subset of required ordering (was: Exchange sort-planning
logic incorrectly avoid sorts when existing ordering is subset of required
ordering)
> Exchange sort-planning logic incorrectly avoid sorts when existing ordering
> is non-empty subset of required ordering
> --------------------------------------------------------------------------------------------------------------------
>
> Key: SPARK-11135
> URL: https://issues.apache.org/jira/browse/SPARK-11135
> Project: Spark
> Issue Type: Bug
> Components: SQL
> Reporter: Josh Rosen
> Assignee: Josh Rosen
> Priority: Blocker
>
> In Spark SQL, the Exchange planner tries to avoid unnecessary sorts in cases
> where the data has already been sorted by a superset of the requested sorting
> columns. For instance, let's say that a query calls for an operator's input
> to be sorted by `a.asc` and the input happens to already be sorted by
> `[a.asc, b.asc]`. In this case, we do not need to re-sort the input. The
> converse, however, is not true: if the query calls for `[a.asc, b.asc]`, then
> `a.asc` alone will not satisfy the ordering requirements, requiring an
> additional sort to be planned by Exchange.
> However, the current Exchange code gets this wrong and incorrectly skips
> sorting when the existing output ordering is a subset of the required
> ordering. This is simple to fix, however.
> This bug was introduced in https://github.com/apache/spark/pull/7458, so it
> affects 1.5.0+.
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