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From chunhui-shi <...@git.apache.org>
Subject [GitHub] drill pull request #797: DRILL-5286: No need to convert when the relNode and...
Date Sun, 26 Mar 2017 05:53:06 GMT
Github user chunhui-shi commented on a diff in the pull request:

    https://github.com/apache/drill/pull/797#discussion_r108052498
  
    --- Diff: exec/java-exec/src/main/java/org/apache/drill/exec/planner/physical/SubsetTransformer.java
---
    @@ -45,15 +48,20 @@ public RelTraitSet newTraitSet(RelTrait... traits) {
     
       }
     
    -  boolean go(T n, RelNode candidateSet) throws E {
    +  public boolean go(T n, RelNode candidateSet) throws E {
         if ( !(candidateSet instanceof RelSubset) ) {
           return false;
         }
     
         boolean transform = false;
    +    Set<RelNode> transformedRels = Sets.newHashSet();
         for (RelNode rel : ((RelSubset)candidateSet).getRelList()) {
           if (isPhysical(rel)) {
             RelNode newRel = RelOptRule.convert(candidateSet, rel.getTraitSet().plus(Prel.DRILL_PHYSICAL));
    +        if(transformedRels.contains(newRel)) {
    --- End diff --
    
    this " if(transformedRels.contains(newRel))" is to check if the newRel is the _same_ object
we got before, it is not to check a 'equal' node. So no hashCode or equal function required.
    
    And yes, I did step into this code and it is doing what we want: for the same node(n)
to be converted in below convertChild() and the same equivalent set(newRel), we don't need
to run the rule again, since we are going to get the same result, and that result will be
added to the same set. So we are very sure we could skip convertChild() for this pair of input(n,
newRel) since this has been called before.
    
    In some cases it can reduce the same rule from running 16 times to 4 times and saved hundreds
ms.



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