[GitHub] HyukjinKwon commented on a change in pull request #23830: [SPARK-26935][SQL]Skip DataFrameReader's CSV first line scan when not used

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HyukjinKwon commented on a change in pull request #23830: [SPARK-26935][SQL]Skip DataFrameReader's CSV first line scan when not used
URL: https://github.com/apache/spark/pull/23830#discussion_r258362101
 
 

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 File path: sql/core/src/main/scala/org/apache/spark/sql/DataFrameReader.scala
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 @@ -508,7 +508,12 @@ class DataFrameReader private[sql](sparkSession: SparkSession) extends Logging {
       sparkSession.sessionState.conf.sessionLocalTimeZone)
     val filteredLines: Dataset[String] =
       CSVUtils.filterCommentAndEmpty(csvDataset, parsedOptions)
-    val maybeFirstLine: Option[String] = filteredLines.take(1).headOption
+    val maybeFirstLine: Option[String] =
+      if (userSpecifiedSchema.isEmpty || parsedOptions.headerFlag) {
 
 Review comment:
   not a big deal but I think you can use `isDefined` instead of `isEmpty`.

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