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From chenghao-intel <...@git.apache.org>
Subject [GitHub] spark pull request: [SPARK-10371] [SQL] Implement subexpr eliminat...
Date Fri, 06 Nov 2015 06:15:48 GMT
Github user chenghao-intel commented on the pull request:

    https://github.com/apache/spark/pull/9480#issuecomment-154316345
  
    In general, I think we'd better add more IR (Intermediate Representation, should be the
Expression or Logical Plan node here) for common sub expression cases, and we then we can
identify the common sub expressions and transform to the new IRs, which should be more clean
for code gen part of work.
    
    As the codegen code is a runtime behavior, which is difficult to debug and maintain, more
IR will be helpful for this case, and that's also how a modern compiler works.
    
    And I don't think the approach I described can be done right now, it's will be a big change,
actually, we have lots of similar optimization like "Common Table Expression" (CTE), or self
join can be optimized in the same way, it will be cool if we can figure a approach for the
general common xxx elimination.


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