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_r258163361
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File path: sql/core/src/main/scala/org/apache/spark/sql/DataFrameReader.scala
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@@ -508,7 +508,14 @@ 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 needsFirstLine: Boolean =
+ userSpecifiedSchema.isEmpty || parsedOptions.headerFlag
+ val maybeFirstLine: Option[String] =
+ if (needsFirstLine) {
+ filteredLines.take(1).headOption
Review comment:
The indentation of this is still off. The title on the PR still needs to be
updated, with a JIRA. Please see my other comment. You can probably inline
`needsFirstLine` too to keep it simpler.
Otherwise I think this is pretty OK, AFAIK, the first line is never needed
unless it's a header or needed for schema inference.
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