spark RemoveRedundantAggregates 源码

spark RemoveRedundantAggregates 代码

文件路径：/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/RemoveRedundantAggregates.scala

/*
 * 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 org.apache.spark.sql.catalyst.analysis.PullOutNondeterministic
import org.apache.spark.sql.catalyst.expressions.{AliasHelper, AttributeSet, ExpressionSet}
import org.apache.spark.sql.catalyst.expressions.aggregate.AggregateExpression
import org.apache.spark.sql.catalyst.plans.logical.{Aggregate, LogicalPlan, Project}
import org.apache.spark.sql.catalyst.rules.Rule
import org.apache.spark.sql.catalyst.trees.TreePattern.AGGREGATE

/**
 * Remove redundant aggregates from a query plan. A redundant aggregate is an aggregate whose
 * only goal is to keep distinct values, while its parent aggregate would ignore duplicate values.
 */
object RemoveRedundantAggregates extends Rule[LogicalPlan] with AliasHelper {
  def apply(plan: LogicalPlan): LogicalPlan = plan.transformUpWithPruning(
    _.containsPattern(AGGREGATE), ruleId) {
    case upper @ Aggregate(_, _, lower: Aggregate) if isLowerRedundant(upper, lower) =>
      val aliasMap = getAliasMap(lower)

      val newAggregate = upper.copy(
        child = lower.child,
        groupingExpressions = upper.groupingExpressions.map(replaceAlias(_, aliasMap)),
        aggregateExpressions = upper.aggregateExpressions.map(
          replaceAliasButKeepName(_, aliasMap))
      )

      // We might have introduces non-deterministic grouping expression
      if (newAggregate.groupingExpressions.exists(!_.deterministic)) {
        PullOutNondeterministic.applyLocally.applyOrElse(newAggregate, identity[LogicalPlan])
      } else {
        newAggregate
      }

    case agg @ Aggregate(groupingExps, _, child)
        if agg.groupOnly && child.distinctKeys.exists(_.subsetOf(ExpressionSet(groupingExps))) =>
      Project(agg.aggregateExpressions, child)
  }

  private def isLowerRedundant(upper: Aggregate, lower: Aggregate): Boolean = {
    val upperHasNoDuplicateSensitiveAgg = upper
      .aggregateExpressions
      .forall(expr => !expr.exists {
        case ae: AggregateExpression => isDuplicateSensitive(ae)
        case e => AggregateExpression.isAggregate(e)
      })

    lazy val upperRefsOnlyDeterministicNonAgg = upper.references.subsetOf(AttributeSet(
      lower
        .aggregateExpressions
        .filter(_.deterministic)
        .filterNot(AggregateExpression.containsAggregate)
        .map(_.toAttribute)
    ))

    upperHasNoDuplicateSensitiveAgg && upperRefsOnlyDeterministicNonAgg
  }

  private def isDuplicateSensitive(ae: AggregateExpression): Boolean = {
    !ae.isDistinct && !EliminateDistinct.isDuplicateAgnostic(ae.aggregateFunction)
  }
}

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