[GitHub] [spark] peter-toth commented on a diff in pull request #42223: [SPARK-44571][SQL] Eliminate the Join by combine multiple Aggregates

["peter-toth (via GitHub)" <gi...@apache.org>]

peter-toth commented on code in PR #42223:
URL: https://github.com/apache/spark/pull/42223#discussion_r1279041973


##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/EliminateJoinByCombineAggregate.scala:
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@@ -0,0 +1,196 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.sql.catalyst.optimizer
+
+import scala.collection.mutable.ArrayBuffer
+
+import org.apache.spark.sql.catalyst.expressions.{Alias, Attribute, Expression, NamedExpression, Or}
+import org.apache.spark.sql.catalyst.expressions.aggregate.AggregateExpression
+import org.apache.spark.sql.catalyst.plans.{Cross, FullOuter, Inner, JoinType, LeftOuter, RightOuter}
+import org.apache.spark.sql.catalyst.plans.logical.{Aggregate, Filter, Join, LeafNode, LogicalPlan, Project, SerializeFromObject}
+import org.apache.spark.sql.catalyst.rules.Rule
+import org.apache.spark.sql.catalyst.trees.TreePattern.{AGGREGATE, JOIN}
+
+/**
+ * This rule eliminates the [[Join]] if all the join side are [[Aggregate]]s by combine these
+ * [[Aggregate]]s. This rule also support the nested [[Join]], as long as all the join sides for
+ * every [[Join]] are [[Aggregate]]s.
+ *
+ * Note: The [[Aggregate]]s to be merged must not exists filter.
+ */
+object EliminateJoinByCombineAggregate extends Rule[LogicalPlan] {
+
+  private def isSupportedJoinType(joinType: JoinType): Boolean =
+    Seq(Inner, Cross, LeftOuter, RightOuter, FullOuter).contains(joinType)
+
+  // Collect all the Aggregates from both side of single or nested Join.
+  private def collectAggregate(plan: LogicalPlan, aggregates: ArrayBuffer[Aggregate]): Boolean = {
+    var flag = true
+    if (plan.containsAnyPattern(JOIN, AGGREGATE)) {
+      plan match {
+        case Join(left: Aggregate, right: Aggregate, _, None, _)
+          if left.groupingExpressions.isEmpty && right.groupingExpressions.isEmpty &&
+            left.aggregateExpressions.forall(filterNotDefined) &&
+            right.aggregateExpressions.forall(filterNotDefined) =>
+          aggregates += left
+          aggregates += right
+        case Join(left @ Join(_, _, joinType, None, _), right: Aggregate, _, None, _)
+          if isSupportedJoinType(joinType) && right.groupingExpressions.isEmpty &&
+            right.aggregateExpressions.forall(filterNotDefined) =>
+          flag = collectAggregate(left, aggregates)
+          aggregates += right
+        case Join(left: Aggregate, right @ Join(_, _, joinType, None, _), _, None, _)
+          if isSupportedJoinType(joinType) && left.groupingExpressions.isEmpty &&
+            left.aggregateExpressions.forall(filterNotDefined) =>
+          aggregates += left
+          flag = collectAggregate(right, aggregates)
+        // The side of Join is neither Aggregate nor Join.
+        case _ => flag = false
+      }
+    }
+
+    flag
+  }
+
+  // TODO Support aggregate expression with filter clause.
+  private def filterNotDefined(ne: NamedExpression): Boolean = {
+    ne match {
+      case Alias(ae: AggregateExpression, _) => ae.filter.isEmpty
+      case ae: AggregateExpression => ae.filter.isEmpty
+    }
+  }
+
+  // Merge the multiple Aggregates.
+  private def mergePlan(
+      left: LogicalPlan,
+      right: LogicalPlan): Option[(LogicalPlan, Map[Expression, Attribute], Seq[Expression])] = {
+    (left, right) match {
+      case (la: Aggregate, ra: Aggregate) =>
+        val mergedChildPlan = mergePlan(la.child, ra.child)
+        mergedChildPlan.map { case (newChild, outputMap, filters) =>
+          val rightAggregateExprs = ra.aggregateExpressions.map { ne =>
+            ne.transform {
+              case attr: Attribute =>
+                outputMap.getOrElse(attr.canonicalized, attr)
+            }.asInstanceOf[NamedExpression]
+          }
+
+          val mergedAggregateExprs = if (filters.length == 2) {
+            la.aggregateExpressions.map { ne =>
+              ne.transform {
+                case ae @ AggregateExpression(_, _, _, None, _) =>
+                  ae.copy(filter = Some(filters.head))
+              }.asInstanceOf[NamedExpression]
+            } ++ rightAggregateExprs.map { ne =>
+              ne.transform {
+                case ae @ AggregateExpression(_, _, _, None, _) =>
+                  ae.copy(filter = Some(filters.last))
+              }.asInstanceOf[NamedExpression]
+            }
+          } else {
+            la.aggregateExpressions ++ rightAggregateExprs
+          }
+
+          (Aggregate(Seq.empty, mergedAggregateExprs, newChild), Map.empty, Seq.empty)
+        }
+      case (lp: Project, rp: Project) =>
+        val mergedInfo = mergePlan(lp.child, rp.child)
+        val mergedProjectList = ArrayBuffer[NamedExpression](lp.projectList: _*)
+
+        mergedInfo.map { case (newChild, outputMap, filters) =>
+          val allFilterReferences = filters.flatMap(_.references)
+          val newOutputMap = (rp.projectList ++ allFilterReferences).map { ne =>
+            val mapped = ne.transform {
+              case attr: Attribute =>
+                outputMap.getOrElse(attr.canonicalized, attr)
+            }.asInstanceOf[NamedExpression]
+
+            val withoutAlias = mapped match {
+              case Alias(child, _) => child
+              case e => e
+            }
+
+            val outputAttr = mergedProjectList.find {
+              case Alias(child, _) => child semanticEquals withoutAlias
+              case e => e semanticEquals withoutAlias
+            }.getOrElse {
+              mergedProjectList += mapped
+              mapped
+            }.toAttribute
+            ne.toAttribute.canonicalized -> outputAttr
+          }.toMap
+
+          (Project(mergedProjectList.toSeq, newChild), newOutputMap, filters)
+        }
+      // TODO support only one side contains Filter
+      case (lf: Filter, rf: Filter) =>
+        val mergedInfo = mergePlan(lf.child, rf.child)
+        mergedInfo.map { case (newChild, outputMap, _) =>
+          val rightCondition = rf.condition transform {
+            case attr: Attribute =>
+              outputMap.getOrElse(attr.canonicalized, attr)
+          }
+          val newCondition = Or(lf.condition, rightCondition)
+
+          (Filter(newCondition, newChild), outputMap, Seq(lf.condition, rightCondition))
+        }
+      case (ll: LeafNode, rl: LeafNode) =>
+        if (ll.canonicalized == rl.canonicalized) {
+          val outputMap = rl.output.zip(ll.output).map { case (ra, la) =>
+            ra.canonicalized -> la
+          }.toMap
+
+          Some((ll, outputMap, Seq.empty))
+        } else {
+          None
+        }
+      case (ls: SerializeFromObject, rs: SerializeFromObject) =>
+        if (ls.canonicalized == rs.canonicalized) {
+          val outputMap = rs.output.zip(ls.output).map { case (ra, la) =>
+            ra.canonicalized -> la
+          }.toMap
+
+          Some((ls, outputMap, Seq.empty))
+        } else {
+          None
+        }
+      case _ => None
+    }
+  }
+
+  def apply(plan: LogicalPlan): LogicalPlan = {
+    if (!conf.eliminateJoinByCombineAggregateEnabled) return plan
+
+    plan.transformDownWithPruning(_.containsAnyPattern(JOIN, AGGREGATE), ruleId) {
+      case j @ Join(_, _, joinType, None, _) if isSupportedJoinType(joinType) =>
+        val aggregates = ArrayBuffer.empty[Aggregate]
+        if (collectAggregate(j, aggregates)) {
+          var finalAggregate: Option[LogicalPlan] = None
+          for ((aggregate, i) <- aggregates.tail.zipWithIndex

Review Comment:
   Seems like you are trying to merge aggregates in sequential order only. What if the first can't be merged with the rest, but the rest can be merged together?



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