[GitHub] rxin commented on a change in pull request #23271: [SPARK-26318][SQL] Enhance function merge performance in Row

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rxin commented on a change in pull request #23271: [SPARK-26318][SQL] Enhance function merge performance in Row
URL: https://github.com/apache/spark/pull/23271#discussion_r240409211
 
 

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 File path: sql/catalyst/src/main/scala/org/apache/spark/sql/Row.scala
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 @@ -58,8 +58,21 @@ object Row {
    * Merge multiple rows into a single row, one after another.
    */
   def merge(rows: Row*): Row = {
-    // TODO: Improve the performance of this if used in performance critical part.
-    new GenericRow(rows.flatMap(_.toSeq).toArray)
+    val size = rows.size
+    var number = 0
+    for (i <- 0 until size) {
+      number = number + rows(i).size
+    }
+    val container = Array.ofDim[Any](number)
+    var n = 0
+    for (i <- 0 until size) {
 
 Review comment:
   if you want to improve this more, you can try with a while loop here rather than a for loop, without creating the extra 0 until size.
   

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