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From viirya <...@git.apache.org>
Subject [GitHub] spark pull request #18931: [SPARK-21717][SQL] Decouple consume functions of ...
Date Mon, 04 Sep 2017 04:19:15 GMT
Github user viirya commented on a diff in the pull request:

    https://github.com/apache/spark/pull/18931#discussion_r136742019
  
    --- Diff: sql/core/src/main/scala/org/apache/spark/sql/execution/WholeStageCodegenExec.scala
---
    @@ -149,14 +149,146 @@ trait CodegenSupport extends SparkPlan {
     
         ctx.freshNamePrefix = parent.variablePrefix
         val evaluated = evaluateRequiredVariables(output, inputVars, parent.usedInputs)
    +
    +    // Under certain conditions, we can put the logic to consume the rows of this operator
into
    +    // another function. So we can prevent a generated function too long to be optimized
by JIT.
    +    // The conditions:
    +    // 1. The parent uses all variables in output. we can't defer variable evaluation
when consume
    +    //    in another function.
    +    // 2. The output variables are not empty. If it's empty, we don't bother to do that.
    +    // 3. We don't use row variable. The construction of row uses deferred variable evaluation.
We
    --- End diff --
    
    The same reason as above. The variables used to evaluate the row can be out of scope because
row construction is deferred until it is used actually.


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