Github user kiszk commented on a diff in the pull request:
https://github.com/apache/spark/pull/19937#discussion_r155927018
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/joins/SortMergeJoinExec.scala
---
@@ -617,6 +619,7 @@ case class SortMergeJoinExec(
s"""
|while (findNextInnerJoinRows($leftInput, $rightInput)) {
+ | ${leftVarDecl.mkString("\n")}
--- End diff --
Since they are local variable, it takes almost no cost. If they are on CPU
registers, there is no cost. If they are in stack frame, it is up to one
instruction to increase or decrease stack frame size.
WDYT? Did you see huge overhead to create and destroy local variables?
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