Github user JoshRosen commented on a diff in the pull request:
https://github.com/apache/spark/pull/12750#discussion_r61666410
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/json/InferSchema.scala
---
@@ -246,12 +260,40 @@ private[sql] object InferSchema {
}
case (StructType(fields1), StructType(fields2)) =>
- val newFields = (fields1 ++ fields2).groupBy(field =>
field.name).map {
- case (name, fieldTypes) =>
- val dataType =
fieldTypes.view.map(_.dataType).reduce(compatibleType)
- StructField(name, dataType, nullable = true)
+ // Both fields1 and fields2 should be sorted by name, since
inferField performs sorting.
+ // Therefore, we can take advantage of the fact that we're
merging sorted lists and skip
+ // building a hash map or performing additional sorting.
+ val newFields = new java.util.ArrayList[StructField]()
--- End diff --
Using a Java `ArrayList` here is _way_ faster than Scala's own ArrayBuffer.
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