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https://issues.apache.org/jira/browse/SPARK-20939?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Hyukjin Kwon resolved SPARK-20939.
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Resolution: Incomplete
> Do not duplicate user-defined functions while optimizing logical query plans
> ----------------------------------------------------------------------------
>
> Key: SPARK-20939
> URL: https://issues.apache.org/jira/browse/SPARK-20939
> Project: Spark
> Issue Type: Improvement
> Components: Optimizer, SQL
> Affects Versions: 2.1.0
> Reporter: Lovasoa
> Priority: Minor
> Labels: bulk-closed, logical_plan, optimizer
>
> Currently, while optimizing a query plan, spark pushes filters down the query
> plan tree, so that
> {code:title=LogicalPlan}
> Join Inner, (a = b)
> +- Filter UDF(a)
> +- Relation A
> +- Relation B
> {code}
> becomes
> {code:title=Optimized LogicalPlan}
> Join Inner, (a = b)
> +- Filter UDF(a)
> +- Relation A
> +- Filter UDF(b)
> +- Relation B
> {code}
> In general, it is a good thing to push down filters as it reduces the number
> of records that will go through the join.
> However, in the case where the filter is an user-defined function (UDF), we
> cannot know if the cost of executing the function twice will be higher than
> the eventual cost of joining more elements or not.
> So I think that the optimizer shouldn't move the user-defined function in the
> query plan tree. The user will still be able to duplicate the function if he
> wants to.
> See this question on stackoverflow:
> https://stackoverflow.com/questions/44291078/how-to-tune-the-query-planner-and-turn-off-an-optimization-in-spark
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