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https://issues.apache.org/jira/browse/SPARK-20366?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15972243#comment-15972243
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Apache Spark commented on SPARK-20366:
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User 'wzhfy' has created a pull request for this issue:
https://github.com/apache/spark/pull/17668
> Fix recursive join reordering: inside joins are not reordered
> -------------------------------------------------------------
>
> Key: SPARK-20366
> URL: https://issues.apache.org/jira/browse/SPARK-20366
> Project: Spark
> Issue Type: Sub-task
> Components: SQL
> Affects Versions: 2.2.0
> Reporter: Zhenhua Wang
>
> If a plan has multi-level successive joins, e.g.:
> ```
> Join
> / \
> Union t5
> / \
> Join t4
> / \
> Join t3
> / \
> t1 t2
> ```
> Currently we fail to reorder the inside joins, i.e. t1, t2, t3.
> In join reorder, we use `OrderedJoin` to indicate a join has been ordered,
> such that when transforming down the plan, these joins don't need to be
> rerodered again.
> But there's a problem in the definition of `OrderedJoin`:
> The real join node is a parameter, rather than a child. This breaks the
> transform procedure because `mapChildren` applies transform on parameters
> which should be children.
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