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https://issues.apache.org/jira/browse/SPARK-25140?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16586091#comment-16586091
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Apache Spark commented on SPARK-25140:
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User 'maropu' has created a pull request for this issue:
https://github.com/apache/spark/pull/22154
> Add optional logging to UnsafeProjection.create when it falls back to
> interpreted mode
> --------------------------------------------------------------------------------------
>
> Key: SPARK-25140
> URL: https://issues.apache.org/jira/browse/SPARK-25140
> Project: Spark
> Issue Type: Improvement
> Components: SQL
> Affects Versions: 2.4.0
> Reporter: Kris Mok
> Priority: Minor
>
> SPARK-23711 implemented a nice graceful handling of allowing UnsafeProjection
> to fall back to an interpreter mode when codegen fails. That makes Spark much
> more usable even when codegen is unable to handle the given query.
> But in its current form, the fallback handling can also be a mystery in terms
> of performance cliffs. Users may be left wondering why a query runs fine with
> some expressions, but then with just one extra expression the performance
> goes 2x, 3x (or more) slower.
> It'd be nice to have optional logging of the fallback behavior, so that for
> users that care about monitoring performance cliffs, they can opt-in to log
> when a fallback to interpreter mode was taken. i.e. at
> https://github.com/apache/spark/blob/a40ffc656d62372da85e0fa932b67207839e7fde/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Projection.scala#L183
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