content: /*
   * 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.calcite.rel.core;
  
  import org.apache.calcite.plan.RelOptCluster;
  import org.apache.calcite.plan.RelOptCost;
  import org.apache.calcite.plan.RelOptPlanner;
  import org.apache.calcite.plan.RelTraitSet;
  import org.apache.calcite.rel.RelDistribution;
  import org.apache.calcite.rel.RelDistributionTraitDef;
  import org.apache.calcite.rel.RelDistributions;
  import org.apache.calcite.rel.RelInput;
  import org.apache.calcite.rel.RelNode;
  import org.apache.calcite.rel.RelWriter;
  import org.apache.calcite.rel.SingleRel;
  import org.apache.calcite.rel.metadata.RelMetadataQuery;
  import org.apache.calcite.util.Util;
  
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  import java.util.List;
  
  import static java.util.Objects.requireNonNull;
  
  /**
   * Relational expression that imposes a particular distribution on its input
   * without otherwise changing its content.
   *
   * @see org.apache.calcite.rel.core.SortExchange
   */
  public abstract class Exchange extends SingleRel {
    //~ Instance fields --------------------------------------------------------
  
    public final RelDistribution distribution;
  
    //~ Constructors -----------------------------------------------------------
  
    /**
     * Creates an Exchange.
     *
     * @param cluster   Cluster this relational expression belongs to
     * @param traitSet  Trait set
     * @param input     Input relational expression
     * @param distribution Distribution specification
     */
    protected Exchange(RelOptCluster cluster, RelTraitSet traitSet, RelNode input,
        RelDistribution distribution) {
      super(cluster, traitSet, input);
      this.distribution = requireNonNull(distribution, "distribution");
  
      assert traitSet.containsIfApplicable(distribution)
          : "traits=" + traitSet + ", distribution=" + distribution;
      assert distribution != RelDistributions.ANY;
    }
  
    /**
     * Creates an Exchange by parsing serialized output.
     */
    protected Exchange(RelInput input) {
      this(input.getCluster(), input.getTraitSet().plus(input.getDistribution()), input.getInput(),
          RelDistributionTraitDef.INSTANCE.canonize(input.getDistribution()));
    }
  
    //~ Methods ----------------------------------------------------------------
  
    @Override public final Exchange copy(RelTraitSet traitSet,
        List<RelNode> inputs) {
      return copy(traitSet, sole(inputs), distribution);
    }
  
    public abstract Exchange copy(RelTraitSet traitSet, RelNode newInput,
        RelDistribution newDistribution);
  
    /** Returns the distribution of the rows returned by this Exchange. */
    public RelDistribution getDistribution() {
      return distribution;
    }
  
    @Override public @Nullable RelOptCost computeSelfCost(RelOptPlanner planner,
        RelMetadataQuery mq) {
      // Higher cost if rows are wider discourages pushing a project through an
      // exchange.
      double rowCount = mq.getRowCount(this);
      double bytesPerRow = getRowType().getFieldCount() * 4;
      return planner.getCostFactory().makeCost(
          Util.nLogN(rowCount) * bytesPerRow, rowCount, 0);
    }
  
    @Override public RelWriter explainTerms(RelWriter pw) {
      return super.explainTerms(pw)
          .item("distribution", distribution);
    }
  }
  