Github user cloud-fan commented on a diff in the pull request:
https://github.com/apache/spark/pull/12926#discussion_r62971803
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
---
@@ -156,22 +157,60 @@ object SamplePushDown extends Rule[LogicalPlan] {
}
/**
+ * Removes the Project only conducting Alias of its child node.
+ * It is created mainly for removing extra Project added in
EliminateSerialization rule,
+ * but can also benefit other operators.
+ */
+object RemoveAliasOnlyProject extends Rule[LogicalPlan] {
+ // Check if projectList in the Project node has the same attribute names
and ordering
+ // as its child node.
+ private def isAliasOnly(
+ projectList: Seq[NamedExpression],
+ childOutput: Seq[Attribute]): Boolean = {
+ if (!projectList.forall(_.isInstanceOf[Alias]) || projectList.length
!= childOutput.length) {
+ return false
+ } else {
+ projectList.map(_.asInstanceOf[Alias]).zip(childOutput).forall {
case (a, o) =>
+ a.child match {
+ case attr: Attribute if a.name == attr.name &&
attr.semanticEquals(o) => true
+ case _ => false
+ }
+ }
+ }
+ }
+
+ def apply(plan: LogicalPlan): LogicalPlan = {
+ val aliasOnlyProject = plan.find { p =>
+ p match {
+ case Project(pList, child) if isAliasOnly(pList, child.output) =>
true
+ case _ => false
+ }
+ }
+
+ aliasOnlyProject.map { case p: Project =>
+ val aliases = p.projectList.map(_.asInstanceOf[Alias])
+ val attrMap = AttributeMap(aliases.map(a => (a.toAttribute,
a.child)))
+ plan.transformAllExpressions {
+ case a: Attribute if attrMap.contains(a) => attrMap(a)
+ }.transform {
+ case op: Project if op.eq(p) => op.child
+ }
+ }.getOrElse(plan)
+ }
+}
+
+/**
* Removes cases where we are unnecessarily going between the object and
serialized (InternalRow)
* representation of data item. For example back to back map operations.
*/
object EliminateSerialization extends Rule[LogicalPlan] {
def apply(plan: LogicalPlan): LogicalPlan = plan transform {
case d @ DeserializeToObject(_, _, s: SerializeFromObject)
if d.outputObjectType == s.inputObjectType =>
- // A workaround for SPARK-14803. Remove this after it is fixed.
- if (d.outputObjectType.isInstanceOf[ObjectType] &&
- d.outputObjectType.asInstanceOf[ObjectType].cls ==
classOf[org.apache.spark.sql.Row]) {
- s.child
- } else {
- // Adds an extra Project here, to preserve the output expr id of
`DeserializeToObject`.
- val objAttr = Alias(s.child.output.head, "obj")(exprId =
d.output.head.exprId)
- Project(objAttr :: Nil, s.child)
- }
+ // Adds an extra Project here, to preserve the output expr id of
`DeserializeToObject`.
+ // We will remove it later in RemoveAliasOnlyProject rule.
+ val objAttr = Alias(s.child.output.head, "obj")(exprId =
d.output.head.exprId)
--- End diff --
nit: use `Alias(s.child.output.head, s.child.output.head.name)(exprId =
d.output.head.exprId)` to make sure the alias name is same with the attribute
name
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