peter-toth commented on code in PR #46143:
URL: https://github.com/apache/spark/pull/46143#discussion_r2686858040
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sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/regexpExpressions.scala:
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@@ -83,6 +83,27 @@ abstract class StringRegexExpression extends BinaryExpression
matches(regex, input1.asInstanceOf[UTF8String].toString)
}
}
+
+ override def expensive: Boolean = hasExpensiveChild || _expensiveRegex
+
+ private lazy val _expensiveRegex = {
+ // A quick heuristic for expensive a pattern is.
+ left match {
+ case StringLiteral(str) =>
+ // If we have a clear start limited back tracking required.
+ if (str.startsWith("^") || str.startsWith("\\b")) {
+ false
+ } else if (str.contains("+")) {
+ // Greedy matching can be tricky.
Review Comment:
Out of curiosity, why only `+` is considered expensive? Why `*` and `{m,n}`
are not?
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