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https://issues.apache.org/jira/browse/SPARK-15742?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Josh Rosen resolved SPARK-15742.
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Resolution: Fixed
Fix Version/s: 2.0.0
Issue resolved by pull request 13484
[https://github.com/apache/spark/pull/13484]
> Reduce collections allocations in Catalyst tree transformation methods
> ----------------------------------------------------------------------
>
> Key: SPARK-15742
> URL: https://issues.apache.org/jira/browse/SPARK-15742
> Project: Spark
> Issue Type: Improvement
> Components: SQL
> Reporter: Josh Rosen
> Assignee: Josh Rosen
> Fix For: 2.0.0
>
>
> In Catalyst's TreeNode {{transform}} methods we end up calling
> {{productIterator.map(...).toArray()}} in a number of places, which is
> slightly inefficient because it needs to allocate and grow ArrayBuilders.
> Since we already know the size of the final output ({{productArity}}), we can
> simply allocate an array up-front and use a while loop to consume the
> iterator and populate the array.
> For most workloads, this performance difference is negligible but it does
> make a measurable difference in optimizer performance for queries that
> operate over very wide schemas (thousands of columns).
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