viirya commented on a change in pull request #34701:
URL: https://github.com/apache/spark/pull/34701#discussion_r758616810
##########
File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
##########
@@ -2162,6 +2163,74 @@ object RemoveLiteralFromGroupExpressions extends
Rule[LogicalPlan] {
}
}
+/**
+ * Prunes unnecessary fields from a [[Generate]] if it is under a count
aggregation
+ * query.
+ */
+object CountAggregateOptimization extends Rule[LogicalPlan] {
+ private def isLiteralCountAggFun(func: AggregateFunction): Boolean = func
match {
+ case c: Count if c.children.size == 1 &&
c.children(0).isInstanceOf[Literal] => true
+ case _ => false
+ }
+
+ private def isCandidate(agg: Aggregate): Boolean = {
+ if (agg.aggregateExpressions.size == 1) {
+ agg.aggregateExpressions(0) match {
+ case Alias(ae: AggregateExpression, _) if
isLiteralCountAggFun(ae.aggregateFunction) =>
+ true
+ case _ =>
+ false
+ }
+ } else {
+ false
+ }
+ }
+
+ private def pruningFields(agg: Aggregate): LogicalPlan = {
+ agg.transformDownWithPruning(_.containsPattern(GENERATE), ruleId) {
+ case p @ Project(_, g: Generate) if
p.references.intersect(g.outputSet).isEmpty
Review comment:
For the example query, the optimized query plan has the `Project`. I
think it is because column pruning.
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