[GitHub] [spark] mgaido91 commented on a change in pull request #24505: [SPARK-27607][SQL] Improve Row.toString performance

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

mgaido91 commented on a change in pull request #24505: [SPARK-27607][SQL] Improve Row.toString performance
URL: https://github.com/apache/spark/pull/24505#discussion_r280110036
 
 

 ##########
 File path: sql/catalyst/src/main/scala/org/apache/spark/sql/Row.scala
 ##########
 @@ -465,16 +465,34 @@ trait Row extends Serializable {
   }
 
   /** Displays all elements of this sequence in a string (without a separator). */
-  def mkString: String = toSeq.mkString
+  def mkString: String = mkString("")
 
   /** Displays all elements of this sequence in a string using a separator string. */
-  def mkString(sep: String): String = toSeq.mkString(sep)
+  def mkString(sep: String): String = mkString("", sep, "")
 
   /**
    * Displays all elements of this traversable or iterator in a string using
    * start, end, and separator strings.
    */
-  def mkString(start: String, sep: String, end: String): String = toSeq.mkString(start, sep, end)
+  def mkString(start: String, sep: String, end: String): String = {
+    var first = true
+    var i = 0
+    val n = length
+    val builder = new StringBuilder
+    builder.append(start)
+    while (i < n) {
+      if (first) {
 
 Review comment:
   no, I don't think it is a good idea. This is implementation is actually similar to what is done in scala's code for `mkString` and I tried running the benchmark above with the change and it takes ~ 50 ms vs ~ 48 ms. The overhead of the comparison added for each execution of the cycle seems to be dominant wrt saving one variable and assigning it once...

----------------------------------------------------------------
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


With regards,
Apache Git Services

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