Josh Rosen created SPARK-15742:
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Summary: 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
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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