[GitHub] [spark] MaxGekk commented on a change in pull request #27497: [SPARK-30245][SQL][FOLLOWUP] Improve regex expression when pattern not changed

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MaxGekk commented on a change in pull request #27497: [SPARK-30245][SQL][FOLLOWUP] Improve regex expression when pattern not changed
URL: https://github.com/apache/spark/pull/27497#discussion_r376724195
 
 

 ##########
 File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/regexpExpressions.scala
 ##########
 @@ -54,9 +54,20 @@ trait StringRegexExpression extends Expression
     Pattern.compile(escape(str))
   }
 
+  var lastPatternStr: String = null
+  var compiledPattern: Pattern = null
+
   def nullSafeMatch(input1: Any, input2: Any): Any = {
-    val s = input2.asInstanceOf[UTF8String].toString
-    val regex = if (cache == null) compile(s) else cache
+    val patternStr = input2.asInstanceOf[UTF8String].toString
+    val regex = if (cache == null) {
+      if (!(patternStr).equals(lastPatternStr)) {
 
 Review comment:
   Benefits of this optimization depend on how patterns are distributed in a column. For example, if we have:
   
   | string | pattern|
   |-|-|
   |s1|pattern1|
   |s2|pattern2|
   |s3|pattern1|
   |s4|pattern2|
   
   in that case, this optimization can lead to slowdown.

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