viirya commented on a change in pull request #24637: [SPARK-27707][SQL] Prune
unnecessary nested fields from Generate to address performance issue in explode
URL: https://github.com/apache/spark/pull/24637#discussion_r295108915
##########
File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
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@@ -588,6 +588,16 @@ object ColumnPruning extends Rule[LogicalPlan] {
.map(_._2)
p.copy(child = g.copy(child = newChild, unrequiredChildIndex =
unrequiredIndices))
+ // prune unrequired nested fields
+ case p @ Project(projectList, g: Generate) =>
Review comment:
`Generate` is special for another reason. We can't prune an output from its
child even just a nested field of the output is used in the top project list.
The generator could use it.
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