Github user nongli commented on a diff in the pull request:
https://github.com/apache/spark/pull/11274#discussion_r55292723
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/WholeStageCodegen.scala
---
@@ -114,27 +117,67 @@ trait CodegenSupport extends SparkPlan {
}
/**
- * Consume the columns generated from it's child, call doConsume() or
emit the rows.
+ * Returns source code to evaluate all the variables, and clear the
code of them, to prevent
+ * them to be evaluated twice.
+ */
+ protected def evaluateVariables(variables: Seq[ExprCode]): String = {
+ val evaluate = variables.filter(_.code !=
"").map(_.code.trim).mkString("\n")
+ variables.foreach(_.code = "")
+ evaluate
+ }
+
+ /**
+ * Returns source code to evaluate the variables for required
attributes, and clear the code
+ * of evaluated variables, to prevent them to be evaluated twice..
*/
+ protected def evaluateRequiredVariables(
+ attributes: Seq[Attribute],
+ variables: Seq[ExprCode],
+ required: AttributeSet): String = {
+ var evaluateVars = ""
+ variables.zipWithIndex.foreach { case (ev, i) =>
+ if (ev.code != "" && required.contains(attributes(i))) {
+ evaluateVars += ev.code.trim + "\n"
+ ev.code = ""
+ }
+ }
+ evaluateVars
+ }
+
+ /**
+ * The subset of inputSet those should be evaluated before this plan.
--- End diff --
I think this is a good place to document how this whole thing works in a
couple of sentences. Something describing that we defer attribute access in the
generated function. We access all the attributes needed by the operator at the
beginning if it was not already referenced earlier in the pipeline.
Might also update the commit message with this since this is what most of
the patch is about.
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