[GitHub] [spark] cloud-fan commented on a change in pull request #28830: [SPARK-31990][SS] Use toSet.toSeq in Dataset.dropDuplicates

[GitBox <gi...@apache.org>]

cloud-fan commented on a change in pull request #28830:
URL: https://github.com/apache/spark/pull/28830#discussion_r439956403



##########
File path: sql/core/src/main/scala/org/apache/spark/sql/Dataset.scala
##########
@@ -2541,7 +2541,9 @@ class Dataset[T] private[sql](
   def dropDuplicates(colNames: Seq[String]): Dataset[T] = withTypedPlan {
     val resolver = sparkSession.sessionState.analyzer.resolver
     val allColumns = queryExecution.analyzed.output
-    val groupCols = colNames.distinct.flatMap { (colName: String) =>
+    // SPARK-31990: We must keep `toSet.toSeq` here because of the backward compatibility issue
+    // (the Streaming's state store depends on the `groupCols` order).
+    val groupCols = colNames.toSet.toSeq.flatMap { (colName: String) =>

Review comment:
       I think this is good for now.
   
   In the future, this may still be broken by Scala version upgrade, and hopefully @xuanyuanking 's unsafe row validation can detect it. Then we can change it and use a deterministic order.




----------------------------------------------------------------
This is an automated message from the Apache Git Service.
To respond to the message, please log on to GitHub and use the
URL above to go to the specific comment.

For queries about this service, please contact Infrastructure at:
users@infra.apache.org



---------------------------------------------------------------------
To unsubscribe, e-mail: reviews-unsubscribe@spark.apache.org
For additional commands, e-mail: reviews-help@spark.apache.org