[GitHub] [spark] rednaxelafx commented on pull request #29975: [SPARK-33092][SQL] Support subexpression elimination in ProjectExec

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rednaxelafx commented on pull request #29975:
URL: https://github.com/apache/spark/pull/29975#issuecomment-705462436


   https://github.com/apache/spark/pull/29975#issuecomment-705356435
   > sorry for my bad memory, is it an existing issue that subexpression elimination can cause perf regression because of the eager execution? e.g. an expression is inside a condition branch (e.g. CASE WHEN) and may not be evaluated.
   
   It's possible to cause performance regression, but I don't think conditional expressions are going to be an issue. From the latest Spark master: https://github.com/apache/spark/blob/5effa8ea261ba59214afedc2853d1b248b330ca6/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/EquivalentExpressions.scala#L81-L97
   
   You can see that CSE excludes the conditional branches from conditional expressions, so you won't have expressions accidentally hoisted from those branches.
   
   


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