[GitHub] spark pull request #19937: [SPARK-22746][SQL] Avoid the generation of useles...

[kiszk]

Github user kiszk commented on a diff in the pull request:

    https://github.com/apache/spark/pull/19937#discussion_r155949301
  
    --- 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 --
    
    Here is my benchmark result. Is there any your result?
    
    ```
    $ cat Loop.java 
    public class Loop {
      private static int _i;
      private static boolean _b;
     
      public static void main(String[] args){
        Loop l = new Loop();
        long s, e;
        long c1 = 10000000000L;
        long c2 = 100000L;
        int N = 10;
    
        // warmup
        for (int i = 0; i < 1000000; i++) {
          l.inner(10000, 100);
          l.outer(10000, 100);
        }
    
        for (int n = 0; n < N; n++) {
          s = System.nanoTime();
          l.inner(c1, c2);
          e = System.nanoTime();
          System.out.println("inner(ms): " + (e-s) / 1000000);
        }
    
        for (int n = 0; n < N; n++) {
          s = System.nanoTime();
          l.outer(c1, c2);
          e = System.nanoTime();   
          System.out.println("outer(ms): " + (e-s) / 1000000);
        }
      }
     
      public void inner(long c1, long c2) {
        for (long i = 0; i < c1; i++) {
          int v1 = 1;
          boolean v2 = true;
          for (long j = 0; i < c2; i++) {
            _i = v1;
            _b = v2;
          }
        }
      }
     
      public void outer(long c1, long c2) {
        int v1 = 1;
        boolean v2 = true;
        for (long i = 0; i < c1; i++) {
          for (long j = 0; i < c2; i++) {
            _i = v1;
            _b = v2;
          }
        }
      }
    }
    $ java -version
    openjdk version "1.8.0_131"
    OpenJDK Runtime Environment (build 1.8.0_131-8u131-b11-2ubuntu1.16.04.3-b11)
    OpenJDK 64-Bit Server VM (build 25.131-b11, mixed mode)
    $ java Loop
    inner(ms): 2779
    inner(ms): 2779
    inner(ms): 2779
    inner(ms): 2779
    inner(ms): 2779
    inner(ms): 2779
    inner(ms): 2779
    inner(ms): 2779
    inner(ms): 2779
    inner(ms): 2779
    outer(ms): 2779
    outer(ms): 2779
    outer(ms): 2779
    outer(ms): 2779
    outer(ms): 2779
    outer(ms): 2779
    outer(ms): 2779
    outer(ms): 2779
    outer(ms): 2779
    outer(ms): 2779
    ```


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