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;
  
  import org.apache.calcite.plan.RelOptPlanner;
  import org.apache.calcite.plan.RelTraitDef;
  import org.apache.calcite.plan.RelTraitSet;
  import org.apache.calcite.rel.core.Exchange;
  import org.apache.calcite.rel.logical.LogicalExchange;
  
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  /**
   * Definition of the distribution trait.
   *
   * <p>Distribution is a physical property (i.e. a trait) because it can be
   * changed without loss of information. The converter to do this is the
   * {@link Exchange} operator.
   */
  public class RelDistributionTraitDef extends RelTraitDef<RelDistribution> {
    public static final RelDistributionTraitDef INSTANCE =
        new RelDistributionTraitDef();
  
    private RelDistributionTraitDef() {
    }
  
    @Override public Class<RelDistribution> getTraitClass() {
      return RelDistribution.class;
    }
  
    @Override public String getSimpleName() {
      return "dist";
    }
  
    @Override public RelDistribution getDefault() {
      return RelDistributions.ANY;
    }
  
    @Override public @Nullable RelNode convert(RelOptPlanner planner, RelNode rel,
        RelDistribution toDistribution, boolean allowInfiniteCostConverters) {
      if (toDistribution == RelDistributions.ANY) {
        return rel;
      }
  
      // Create a logical sort, then ask the planner to convert its remaining
      // traits (e.g. convert it to an EnumerableSortRel if rel is enumerable
      // convention)
      final Exchange exchange = LogicalExchange.create(rel, toDistribution);
      RelNode newRel = planner.register(exchange, rel);
      final RelTraitSet newTraitSet = rel.getTraitSet().replace(toDistribution);
      if (!newRel.getTraitSet().equals(newTraitSet)) {
        newRel = planner.changeTraits(newRel, newTraitSet);
      }
      return newRel;
    }
  
    @Override public boolean canConvert(RelOptPlanner planner, RelDistribution fromTrait,
        RelDistribution toTrait) {
      return true;
    }
  }
  