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https://issues.apache.org/jira/browse/SPARK-30759?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17033889#comment-17033889
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Dongjoon Hyun commented on SPARK-30759:
---------------------------------------

Hi, [~maxgekk]. As you wrote on the PR, this is a behavior since 1.0.0. So, I 
convert this into an improvement JIRA. That will be easier to understand this 
issue impact and contribution.

> The cache in StringRegexExpression is not initialized for foldable patterns
> ---------------------------------------------------------------------------
>
>                 Key: SPARK-30759
>                 URL: https://issues.apache.org/jira/browse/SPARK-30759
>             Project: Spark
>          Issue Type: Improvement
>          Components: SQL
>    Affects Versions: 3.1.0
>            Reporter: Maxim Gekk
>            Priority: Minor
>         Attachments: Screen Shot 2020-02-08 at 22.45.50.png
>
>
> In the case of foldable patterns, the cache in StringRegexExpression should 
> be evaluated once but in fact it is compiled every time. Here is the example:
> {code:sql}
> SELECT '%SystemDrive%\Users\John' _FUNC_ '%SystemDrive%\\Users.*';
> {code}
> the code 
> https://github.com/apache/spark/blob/8aebc80e0e67bcb1aa300b8c8b1a209159237632/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/regexpExpressions.scala#L45-L48:
> {code:scala}
>   // try cache the pattern for Literal
>   private lazy val cache: Pattern = pattern match {
>     case Literal(value: String, StringType) => compile(value)
>     case _ => null
>   }
> {code}
> The attached screenshot shows that foldable expression doesn't fall to the 
> first case.



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