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https://issues.apache.org/jira/browse/SPARK-20233?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15958265#comment-15958265
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Apache Spark commented on SPARK-20233:
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User 'ioana-delaney' has created a pull request for this issue:
https://github.com/apache/spark/pull/17546
> Apply star-join filter heuristics to dynamic programming join enumeration
> -------------------------------------------------------------------------
>
> Key: SPARK-20233
> URL: https://issues.apache.org/jira/browse/SPARK-20233
> Project: Spark
> Issue Type: Sub-task
> Components: SQL
> Affects Versions: 2.2.0
> Reporter: Ioana Delaney
> Priority: Critical
>
> This JIRA integrates star-join detection with the cost-based optimizer.
> The join enumeration using dynamic programming generates a set of feasible
> joins. The sub-optimal plans can be eliminated by a sequence of independent,
> optional filters. The optional filters include heuristics for reducing the
> search space. For example,
> # Star-join: Tables in a star schema relationship are planned together since
> they are assumed to have an optimal execution.
> # Cartesian products: Cartesian products are deferred as late as possible to
> avoid large intermediate results (expanding joins, in general).
> # Composite inners: “Bushy tree” plans are not generated to avoid
> materializing intermediate result.
> For reference, see “Measuring the Complexity of Join Enumeration in Query
> Optimization” by Ono et al.
> This JIRA implements the star join filter.
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