[GitHub] srowen commented on a change in pull request #23830: Decrease processing overhead on DataFrameReader CSV calls with specif…

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srowen commented on a change in pull request #23830: Decrease processing overhead on DataFrameReader CSV calls with specif…
URL: https://github.com/apache/spark/pull/23830#discussion_r257853015
 
 

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 File path: sql/core/src/main/scala/org/apache/spark/sql/DataFrameReader.scala
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 @@ -508,7 +508,9 @@ 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)
+	filteredLines.take(1).headOption else None
 
 Review comment:
   This indent is off. I might just add the braces and newline for clarity.
   
   Please see https://spark.apache.org/contributing.html ; this one probably needs a JIRA and other modifications.
   
   But more to the point this changes the logic of `linesWithoutHeader`. This seems to skip handling the header too.

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